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Tuning and Adjusting CIS Fuel Injection
 
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Pelican Technical Article:

Tuning and Adjusting CIS Fuel Injection

Talent:

*

Tools:

Mixture adjustment tool

Applicable Models:

Porsche 911 (1974)
Porsche 911 Carrera (1974-75)
Porsche 911S (1974-77)
Porsche 911SC (1978-83)
Porsche 911T (1973)
Porsche 930 Turbo (1976-89)

Parts Required:

Fuel injection manifold hoses

Hot Tip:

Spray carb cleaner around the injectors and hoses to check for vacuum leaks

Performance Gain:

Better running engine

Complementary Modification:

-
101 Projects for Your Porsche 911

This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.

For more than ten years, Porsche used the Bosch K-Jetronic Continuous Injection System (CIS) on all production 911s. The system in general is very reliable, and was only bested in 1984 by the introduction of the Motronic engine management system that controls both ignition and fuel injection together.

The CIS meters the amount of fuel provided to the cylinders as a function of the air drawn into the engine. The CIS air flow sensor plate measures the amount of air that is being drawn into the system. This sensor plate is attached to a fuel distributor that evenly meters the amount of pressurized fuel sent to each injector. The system doesn't differentiate among the six injectors: it sends the same amount of fuel to them at all times. Unlike pulsed-injection systems like the Motronic system or even the earlier Mechanical Fuel Injection system, the CIS injectors distribute fuel to the cylinders at all times. The opening and closing of the intake valves controls the intake of fuel into and out of the combustion chamber.

Through 1979, CIS was a semi-open-looped system, which means that it didn't monitor the output gases from the engine to see if the air/fuel mixture was set at the appropriate levels. In 1980, emissions requirements forced the introduction of an oxygen sensor into the system, which helped the engine to better run at the appropriate mixture level through the regulation of fuel pressure inside the fuel distributor.

MAINTENANCE AND ADJUSTMENT

The two primary adjustments for the CIS are the idle speed and the mixture adjustment. The mixture can be adjusted by turning a small hex screw that is located in-between the fuel distributor and the sensor plate. Use a long hex key, or the special mixture adjustment tool to turn the screw.

The screw is indexed so that it should click when you rotate it. Turn it clockwise to richen up the mixture, or counterclockwise to lean it out. The mixture should only be adjusted when the car is hooked up to a CO meter. Make sure that you rev the engine for a few seconds before you take a reading from the meter, and that you don't leave the tool in the adjustment screw: the screw itself must be free to move up and down without any weight on it.

The idle speed is adjusted by allowing more air to bypass the closed throttle. Using a large flathead screwdriver, simply rotate the screw clockwise to reduce the idle, and counter clockwise to increase it. The idle should be set to be about 950 rpm.

TROUBLESHOOTING

So what can go wrong on with the CIS? Plenty. Although the CIS has a reputation for reliability, it is also known for having a few characteristic problems. Warm and cold start problems are common, as well as backfiring and poor performance at startup. On the early 911s, the CIS didn't even operate properly, until the car was warmed up. A hand throttle was a standard part of the car in order to facilitate easier starting and warm-up. On the later model CIS cars, the addition of the auxiliary air valve eliminated the need for the hand throttle.

One of the most common problems for the older CIS cars is the existence of vacuum leaks. The entire system works almost entirely on vacuum. Any vacuum leaks will cause problems in regulating the mixture, and may also result in an uneven idle. To check for vacuum leaks, spray some carb cleaner or starting fluid around the hoses and injectors of the fuel injection system. If the engine idle increases, then you probably have a vacuum leak that needs to be tracked down. Make sure that you have a fire extinguisher handy: if there is arcing in the spark plug wires, you may ignite the carburetor cleaner.

Another common problem is the warm-up regulator (WUR), or control pressure regulator. Contrary to popular belief, the WUR regulates fuel pressure in the system at all times. Cars that experience difficulty adjusting the mixture on may be suffering from a defective WUR. This failure may also contribute to starting problems.

Since the CIS depends upon correct fuel pressure for proper operation, the fuel pump and fuel accumulator must be in working order. Using a CIS fuel pressure tester, verify the proper operation of the fuel pump by measuring the pressure when the ignition is turned on. The pressure measurements need to be taken at specific times, and at varying engine temperatures. For more details on these specifications, see the Porsche Technical Specification Book for your year 911. Also make sure that your fuel accumulator (Pelican Technical Article: Fuel Filter and Accumulator Replacement) and the pressure check valve in the fuel pump are operating properly.

Sometimes the idle on the CIS cars will oscillate up and down. An incorrectly set mixture will often cause this to occur. Recheck the mixture with an exhaust gas analyzer to make sure you are in the proper operating range.

Hot start problems are common with CIS systems and may be caused by a faulty fuel accumulator (see Pelican Technical Article: Fuel Filter and Accumulator Replacement) or a faulty fuel pressure check valve in the fuel pump (see Pelican Technical Article: Fuel Pump Replacement). Cold start problems can often be attributed to the thermo-time switch or the warm-up regulator.

For more information than you will probably every need on the CIS, take a look at the book, "Bosch Fuel Injection & Engine Management" by Charles O. Probst. It provides an excellent guide for understanding the physics behind the CIS, and also includes an invaluable troubleshooting section.

The CIS idle speed is set in a similar manner to the setting of the speed on carburetors and the MFI system.
Figure 1

The CIS idle speed is set in a similar manner to the setting of the speed on carburetors and the MFI system. A throttle bypass system regulates the amount of air that passes into the fuel injection system when the throttle is at rest. This screw is indicated by the white arrow. You should adjust the idle until it reaches about 950 rpm. If you have problems achieving this setting, then you might want to double check the mixture adjustment.

The mixture is adjusted by placing the adjustment tool in-between the fuel distributor and the large rubber boot (shown by arrow).
Figure 2

The mixture is adjusted by placing the adjustment tool in-between the fuel distributor and the large rubber boot (shown by arrow). The screw is indexed so that you can feel distinct 'clicks' as you rotate it. Turn it clockwise to richen up the mixture, and counter clockwise to lean it out. Make sure that you have the exhaust gases checked while you are performing the adjustment so that you can verify that you are in the proper operating range.

The intake manifold hoses (shown by arrow) are common sources for vacuum leaks.
Figure 3

The intake manifold hoses (shown by arrow) are common sources for vacuum leaks. If the carb cleaner spray test indicates that there is indeed a vacuum leak near the hoses, then they should be replaced. Unfortunately, this requires the removal of the fuel injection from the top of the motor: a task that is not easy considering the tight clearances in the engine compartment. Also a source of vacuum leaks are the injector seals and the plastic inserts that fit into base of the intake manifolds. Check and replace these if you find evidence of vacuum leaks near the base of the manifolds.

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Comments and Suggestions:
Steven Comments: I see that you can buy a gas meter device to measure the CO in tail pipe fairly inexpensively. I would like to get one to properly adjust the fuel mixture on my 1977 911. What should the CO reading at the tail pipe be when the fuel mixture is adjusted correctly? The video for the CO meter stated 3.0 for a VW beetle. I got the impression that it should be the same for other engines as well. Thanks for any information.
November 19, 2016
  Followup from the Pelican Staff: It's not s easy as a single setting, it varies. see attached. - Nick at Pelican Parts
MISTER FIX IT Comments: I have a 1977 911S that has this bucking, missing engine micro hesitation, talked about above. It has been to one shop for months, where they fixed everything else, but when finally returned had the same bucking problems, 1800 to 2500 rpm and only runs a tiny bit better when warm. I then took it to another shop for a second repair opinion and expense where the fuel accumulator was deemed faulty, replaced and did fix the hard no start problem. I was asked to test drive the car under the assurances that additional timing and fidixing was performed and that it should perform better. Well it was worse and returned to the shop for further experimentation and sent off to have it dyno tested with electronic monitoring devices hooked up. Both of the shops that my car have visited are very reputable outfits here in Sacramento. It sounds like this stuttering problems happens with the 2.7 engines. Have you come up with a good solution for this problem?
June 26, 2016
  Followup from the Pelican Staff: You have to determine the cause by testing the engine when the problem is present. Spark, compression and fuel delivery all have to be tested. Good direction can be found using a secondary ignition scope. - Nick at Pelican Parts  
MichaelW Comments: Hi team. I own a gorgeous 11/1976 911 2.7 liter Sporto and have had her for a little over 6 months now. She has no power brakes, no power steering, no power windows or any of those other "luxuries" that we seem to take for granted. She's simple, but she handles and goes absolutely beautifully. To say that it was love at first sight is an understatement! This morning she started up and took off okay. A mile or so up the road I stopped at a red light and she seemed to develop a rough almost jerky idle. The red alternator light briefly lit up a couple of times and she sounded like she was almost going to stall. I gave a bit of a tap on the accelerator and she was fine. A couple of miles up the road, the same thing happened. After a few more times she eventually stalled at red lights on a steep hill. The exhaust gas smelled quite rich on startup and was a little smokey, but there were no issues starting her up. She started first time. I take her for a decent run each weekend and until today she’s been running perfectly. I checked the belt and it seemed tight enough has just enough give in it when I apply pressure with my finger. How tight does it need to be? Should I replace it anyway or do I need to order a service kit, change the plugs etc? Thanks heaps in advance.
June 12, 2016
  Followup from the Pelican Staff: The battery light likely came on due to the drop in RPM.

i would check the oil level to see if it using oil. Also check the engine for vacuum leaks. - Nick at Pelican Parts
 
2011BH Comments: Hi, Bernie from Australia. Have an '83 SC 204 HP Aust. delivered car. Problems with not wanting to rev stutters & lacking power. Had a vacuum leak test done last week nil problems. Some tests done in May were:
COMPRESSION PRESSURES ALL 180-185 PSI
INJECTOR PUMP SYSTEM PRESSURE 5.2 BAR
CONTROL PRESS. 2.8 BAR, 1.2LITRES IN 30 SECS FLOW
INDIVIDUAL INJECTOR FLOWS 18 TO 22 CC'S ROUGHLY WITHIN 6%}
INJ. SPRAYS ARE OK
Vacuum leak tests OK.
Any ideas to help sort this one out please.
June 6, 2016
  Followup from the Pelican Staff: have you checked exhaust backpressure? You want less than 1 PSI. Also check spark Kv output. - Nick at Pelican Parts  
theweaver Comments: Hello, I have a 1980 SC. I rebuilt the engine 1500 miles ago. It runs and starts fine, except that after a few seconds from cold, the engine revs up on its own, then slows down , and revs again, and repeats for about a minute or so, then once warm a little it runs ok. However, when I drive the car it is lumpy and gives the feeling of a misfire, but runs perfectly ok above 3K revs.
Could this be a weak mixture or an air leak or both.
June 5, 2016
  Followup from the Pelican Staff: it sounds like a vacuum leak trying to be controlled, once warm it goes away. - Nick at Pelican Parts  
Paul Comments: I have a 82, 911SC. starts easy cold. After I drive it for a while and shut it off, I have a hard time stating the warm engine. this only happens after it sits for 15 minutes or more. Where do I start?
May 23, 2016
  Followup from the Pelican Staff: When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
blown daytona Comments: Hi, I have a 85 930 with B&B headers and Schnell muffler. Should I use the factory CO setting or do you recommend a higher or lower number. Thanks
May 14, 2016
  Followup from the Pelican Staff: Stick with the factory setting. - Nick at Pelican Parts  
JCFL Comments: Hello, 2nd question tonight, getting ready to put the car on the road. I write from Eastern Canada.

I have a 1982 911 SC with 150,000 miles, which drives very well. Last fall, I drove right until December 8th, when the weather is much colder than in the summer months.

I noticed that the car performed much better during the cold November and December weather than during the warmer summer months, so I assume that my CIS adjustment is not quite up to par.

Can you guide me as to how to get this kind of cold weather performance during the warmer summer months ? Thank you
April 23, 2016
  Followup from the Pelican Staff: It could be. If you think it needs adjustment, have the tailpipe emissions checked to confirm, before you try to make adjustments. - Nick at Pelican Parts  
DaKipster Comments: I have a 1986 911 3.2 that failed the California smog test due to low CO%. So I did the obvious and changed the catalyst converter the second one in 4yrs. So, I'm sure it will pass. But it also running Lean 00.1 and according to sources if not corrected, it can ruin the new cat. What's your suggest to find and correct the running to lean issue? The old cat converter looks clean looking in.
March 6, 2016
  Followup from the Pelican Staff: Likely failed due to low Co2%. If that is true, you have an efficiency problem. Could be either an exhaust leak, or the cat was in fact faulty. I would need to know all the test results, when it failed to offer more insight.- Nick at Pelican Parts  
Fatdaddy Comments: I have a 1974 911sc with a 2.7. Issues....well... where do I start. It's possessed!!! It was stored for more then 15 years. It's in original condition. Still looks great. I've replaced injectors, injector o-rings, WUR, Fuel pump, fuel filter, spark plugs, cap and rotor, points, etc.. I've done a smoke test, found a couple small leaks, compression test 60/110 all six cylinders, cylinder leak down test, checked and adjusted the timing so many times I've lost count. ok the issue: Start's right up. idle "ok" pops and misses ever so slightly. cold and warmed up. when I drive it. pops and continues to surge during acceleration. i've tried to adjust the idle air/fuel mixture a fuel times. Continues to act up..Any ideas???
December 27, 2015
  Followup from the Pelican Staff: adjusting the air fuel mixture can be a troublemaker. If it is not the problem root, then you are adding to the issue. I would start by resetting the mixture to base. Then checking for vacuum or air leaks. Popping is usually caused by a lean condition or a timing issue. - Nick at Pelican Parts  
bennyandthek-jet Comments: Sorry also, it stalls dead and will not start again until cold. Could the aux air valve be causing a lean condition difficult cold start up and then causing the dead stall/ no start?
December 16, 2015
  Followup from the Pelican Staff: Got it. thanks. - Nick at Pelican Parts  
bennyandthek-jet Comments: 1974 Porsche 911 2.7 difficult to start unless depressing the air/ fuel lever in the airbox slightly while cranking.will then run fine with great throttle response after a few minutes. But after idling for fifteen minutes or so it stalls dead as if the ignition coil loses power. The wur is operational as is the thermo switch, microswitch and seemingly the cold start injector.the injectors do not leak and flow properly . I am perplexed. Any ideas?
December 16, 2015
  Followup from the Pelican Staff: If you have to press the plate / lever, the issue may be a vacuum leak. If you have insufficient vacuum, the plate will not move, blocking fuel flow. - Nick at Pelican Parts  
junjun1q Comments: Can i swap the CIS system from a '78 SC to a '75 911S?
November 14, 2015
  Followup from the Pelican Staff: I am not 100% sure.
I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
 
Dick Comments: Have a 77 911 2.7 that hesitates or chugs between 2000-2500 RPMS both while accelerating and at steady RPMs. Seems to improve slightly as engine warms up. Car has been checked out by a qualified mechanic. They put it on a dyno. Fuel and vacuum pressures are ok and warm up regulator replaced, ignition/vacuum ok. Mechanic is at a loss. Any ideas? Could it be fuel injectors, fuel distributor/
November 12, 2015
  Followup from the Pelican Staff: Something was missed during the diagnosis. I would monitor air / fuel ratio when the problem occurs. Check if the system is losing fuel delivery or if it is an air leak. - Nick at Pelican Parts  
Michael Comments: i got 911 3.0 SC, it backfires when i try to give it gas, if then move the gas throttle and lift the airflow sensor with my finger at the same time, the engine sounds perfect and don't backfire, i have checked for vacuum leaksOK, checked the fuel distributor and the glider insideOK, tried to adjust the mixture with no luck, adjusted the timing, i have change the fuel pump, new fuel filter, new spark plugs, new ignition distributor and rotor, starts up cold and runs with higher rpm and then when it's warm dropped in RPM to 800-900 RPM, no problem starting when it's warm.

all in all, when i help the airflow sensor and throttle at the same time the engine takes RPM with no problem.

BR
Michael
November 9, 2015
  Followup from the Pelican Staff: Likely an air leak in the intake manifold. Check that it is sealed and leak fdree. - Nick at Pelican Parts  
Dom G Comments: Hi. My 1983 911 SC starts fine. If i don't let it warm up complety, it knocks and backfires for a minute or two. Then, at low rpms, it hesitates. Runs great when i step on gas hard. If i let the engine warm up completley, it runs great until the temp drops. Then the hesitation returns. Fuel pressure and mixture is ok. Replaced plugs, wires, distributor cap and ignition rotor. Thoughts on what might be?
October 18, 2015
  Followup from the Pelican Staff: Sounds like a vacuum leak or timing issue. - Nick at Pelican Parts  
Jumpin jack Comments: I have a 1982 911 sc.The car starts fine.After warming up after a run and the car is at idle it runs erraticly and then stalls.The car restarts ok.Your advise would be greatly appreciated
September 21, 2015
  Followup from the Pelican Staff: Sounds like an engine misfire or fuel delivery issue. I would check spark, fuel and compression on all cylinders.
- Nick at Pelican Parts
 
Alex Comments: I have a 1979 911SC, and would like to know if I can install/switch it for a 1980 fuel distributor with part number 0438 100 077. My fuel distributor reads 0438 100 031
September 19, 2015
  Followup from the Pelican Staff: I’m not the best with part numbers.

Give our parts specialists a call at 1-888-280-7799. They can figure out if it will fit.
- Nick at Pelican Parts
 
Hakalaxi Comments: Hi, Porsche 930 1979, fuel "system" pressure. When only primary pump in operation front pump I will get 5,2bar... when I connect also secondary pump rear pump, no change on pressure level. You can hear secondary pump running but seems like it does not give any additional pressure increase. Do you have nominal pressure levels for primary and secondary pumps... and what is the correct overall system pressure?
Warm control pressure is 3,5bar and engine is running smoothly. I have some issues with cold start.
Thank you for your support.
September 15, 2015
  Followup from the Pelican Staff: I only have info as far back as 1982:

Diagram for warm-up regulator Part No.911.606.105.08 Bosch

Control pressure "warm" 3.4 to 3.8 bar
System pressure Testing value 4.5 to 5.2 bar
Adjusting value 4.7 to 4.9 bar
Leak Test
Min. press. after 10 min. 1.3 bar
after 20 min. 1.1 bar
Fuel Injectors Opening pressure 2.5 to 3.6 bar



I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
 
Todd V. Comments: Nick, again-thanks for your input on getting the injectors out of my 1981 911 SC. My injectors will turn freely in the sleeve and I can tug on them-but it's a no go to get them out. I have seen a Porsche tool in pictures that seems to work, it looks like a piece of metal fuel tubing with a cross attachment that you can pull on-the other end screws down over the injector-does your company have anything like that?
August 28, 2015
  Followup from the Pelican Staff: We may be able to get you one. Give our parts specialists a call at 1-888-280-7799. They can help you find the right tool. - Nick at Pelican Parts  
Mopar Comments: I'm sorry what leak did you describe, I don't see that one. Thanks for your time on this.
August 21, 2015
  Followup from the Pelican Staff: An air in the intake manifold. - Nick at Pelican Parts  
Todd V. Comments: Nick, thanks for the response. Any sure-fire way to get the injectors out so I can replace them. Looks like original equipment-very stubborn, seems like using vice grips is a little crude! Thanks
August 20, 2015
  Followup from the Pelican Staff: Once you have the lines off, allow some penetrating oil to soak in around the injector, then rotate the injector as you pull it out. - Nick at Pelican Parts  
Todd V. Comments: "I have a 1981 Porsche 911 SC, it has approx 37,000 miles. I let the vehicle sit for approx 1 month without starting. In the past this has not been a problem...although on occasion after leaving it for 1-2 weeks it would start fine, but seems to be running on 5 cyls. After a short drive the vehicle will "Clear It's Throat" and have strong pull, good idle with no issues on restart. I pulled plugs to ascertain which cyl is not up to specs, looks like #3 is just darker, not wet, oily or a great deal of build-up. I am attempting to pull the #1 injector...very stubborn-it rotates and feels loose but will not come out-don't feel like I want to use my steel fuel lines to pull it free, any other suggestions? When I disconnected the fuel line from #1 injector, there was a good deal of flaky contamination at the junction. I know without close inspection it's very difficult to have a take on my fuel system-does the fuel system have this type of contamination throughout? Is there a reliable system flush for the entire system from Tank, Pump, Fuel Distributor, Injectors ect that you could recommend? Thanks
August 18, 2015
  Followup from the Pelican Staff: No flush. You can have the fuel tank cleaned and fuel distributor rebuilt. The rest maybe soak in fuel.- Nick at Pelican Parts  
Mopar Comments: Yes the fuel pressure is the same,barely coming out of return line on fuel distributor.
August 17, 2015
  Followup from the Pelican Staff: Then probably the leak I described. - Nick at Pelican Parts  
Turbo Comments: Thanks for the response. I was stranded on side of road and had to tow car home. The car backfired and died after that I would only start and idle for a few seconds then die then it ran long enough for me to get it off the road and could not keep it running. Towed it home and now it won't start at all. Any further advice ? Thank you.
August 16, 2015
  Followup from the Pelican Staff: Original comment remains. If you have a large leak, the fuel plate will not be activated, no fuel to injectors, no start. Check for a large vacuum leak or damage at the intake manifold or plenum. - Nick at Pelican Parts  
Turbo Comments: 1983 930 turbo new engine runs great for awhile then hit the throttle turbo spools up and engine dies. Restarts but then just dies wait awhile then it fires up and runs for a few minutes and dies crank it it starts then just dies??? I drove it for 50 miles ran fine got on highway punched it backfires and dies. The car crackles and spits I dealing down hill and seems to back fire after getting on it.
August 15, 2015
  Followup from the Pelican Staff: I would check for an intake leak or duct that has an air leak. This is commonly related to the symptoms you are describing. - Nick at Pelican Parts  
mopar Comments: I can't get my fuel pressure down, with in a couple of minutes my plugs foul out. Is there a way to put just a aftermarket adjustable pressure regulator to control my own pressure.
August 6, 2015
  Followup from the Pelican Staff: With the return line removed and feeding fuel into a suitable storage container, is fuel pressure the same? - Nick at Pelican Parts  
mopar Comments: I have a 81 porshe 924 turbo, my fuel pressure is 92 psi at the fuel distributor and from the frequency valve going back into the distibuor. I checked and made sure that my return line was ok. I'm at lost of what to do...help
August 5, 2015
  Followup from the Pelican Staff: What are you trying to fix? - Nick at Pelican Parts  
kjmacke Comments: Have a 1979 928. Ran a test on the system pressure on the cis. It came up with 9 bar or about 130 psi. Wow way too much tried to remove some shims in regulator did not change a thing. I am stumped any help would be greatly app. or else the car is going to the junk yard. Its getting old. THANKS KELLY
July 14, 2015
  Followup from the Pelican Staff: have you checked if the return is restricted? - Nick at Pelican Parts  
Mark Comments: new rebuilt engine. cause of engine failure excess fuel in one cylinder now excessive fuel in all cylinders while cranking engine. engine will fire with fuel pump disabled on either, why excessive fuel only while cranking?
July 6, 2015
  Followup from the Pelican Staff: You may have a leaking injector. Not noticeable when engine running. - Nick at Pelican Parts  
mark Comments: i have 1980 911sc 3.0 . filled cylinder full of gas blew piston apart. I did a complete engine rebuild. Trying to start engine for first time since rebuild I am getting way to much fuel to cylinders, severly flooding engine. I did install new injectors and clean fuel tank and system I have not done anything to fuel distributor Why so much fuel?
July 4, 2015
  Followup from the Pelican Staff: Fuel pressure may be too high, or you have a stuck open injector. I would start by checking the injector of the cylinder that failed. You may find the root cause there. - Nick at Pelican Parts  
Davids Comments: Hi A get the porsche 911 turbo 1987, and dont start,a checked spark and fuel pressure and is ok, want is wrong in my car?
July 2, 2015
  Followup from the Pelican Staff: If it has spark and fuel, engine timing may be off. Check engine compression. - Nick at Pelican Parts  
FLYT 911 Comments: How difficult is it to replace the fuel lines in 1979 911SC? There is a belly pan and the mechanic claims he would need to go through the floor boards.
June 6, 2015
  Followup from the Pelican Staff: You can do it by dropping the engine and trans, then pulling them out the tunnel. See this discussion:

http://forums.pelicanparts.com/porsche-911-technical-forum/155892-replacing-pressurized-fuel-line-pump-78-sc.html #post1281740 - Nick at Pelican Parts
 
JCISCOTT Comments: My 83 911SC was running great... have 6000 miles on a totally rebuilt motor. Would not start one day.. I fiddled with the fuel pump fuse and relay and got it going. Changed the pump and relay and back in business... a few days later, it started to stumble really bad ONLY WHEN HOT and below 2000 RPM.. get above 2000 rpm and it runs like a champ... runs great when cold... definitely running too lean when hot at low RPM...

I looked at all the vac lines and intake hoses... all look good... I notices that the CIS plate is very difficult to move up and down when hot, but easy to move when cold...
so... should the CIS plate move real easy when both cold and warm ?? what would make it hard to move when HOT ??
May 29, 2015
  Followup from the Pelican Staff: Do not press on the CIS plate. Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders.
- Nick at Pelican Parts
 
Chaz Comments: Hi, I have a 1976 2,7 Targa which I tinker around on and enjoy the rides when I have them but I also have this "BUCKING" problem especially when she warms up and after changing gears. Once the gear is changed and I increase excelleration she is ok until I reach cruising speed in any of that gears then she starts bucking again. Very frustrating. Any thoughts. Thanks
May 28, 2015
  Followup from the Pelican Staff: Bucking can be many different things, but in my experience this is usually caused by a bad distributor (too much play in shaft up and down), or mis-adjusted idle or fuel mixture. Assuming your cars maintenance is up to date...Check the basics first, fuel pressures, check for intake leaks, check the fuel mixture, check and or adjust the ignition timing, then set the idle. - Casey at Pelican Parts  
gilles Comments: I have a Porsche 911 3.0 carrera, I do a thesis. when my car for the first time he started functioned well, but after starting the second time, the engine started, but stopped again. when the air flow sensor plate served wast the engine continued to run.but when you operate the accelerator pedal, the engine does not respond

there could someone help me?
I would be very grateful to you
May 19, 2015
  Followup from the Pelican Staff: If your car has CIS...My guess is that the fuel pump check valve is faulty. When you lift the sensor plate you are priming the system with fuel. When the check valve is faulty the system bleeds its residual pressure back in to the tank, which is why he doesn't respond to pumping the throttle.

You can find it here about halfway down the page there are two choices. Both are quality parts.
http://www.pelicanparts.com/catalog/SuperCat/0801/POR_0801_FULFUL_pg3.htm #item4 - Casey at Pelican Parts
 
Targa4now Comments: Insightful CIS troubleshooting video

Bosch K-Jetronic explained on YouTube: http://youtu.be/a4fJAfXYxWk
April 13, 2015
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
Dallas Comments: I have a '79 911 S/C modified to look like a Carrera. It has probably one of the strangest problems I've ever seen in a car. I go to it and start it, and it will run good well, it runs kind of rich, but I would think that's another problem for a couple hours of driving until fire is cut off completely. It doesn't sputter or pop or anything this leads me to believe it isn't a fuel problem, it just dies and will not start again. Doesn't even try to fire up. It seems like I can take it back to my shop and disconnect the battery and reconnect it a little while later it will fire right up. I guess I can drive it another couple hours and it will do it again. I've spoken with several mechanics including Porsche of New Orleans themselves and no one has ever heard of this. Please help!

Thanks,
Dallas Freeman
March 22, 2015
  Followup from the Pelican Staff: Sounds like an ignition issue to me.

Find out what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
Gabriele Comments: Hi ti everyone!
I'm working in a SC 3.0
The car start very bad, but playing with the throttle pedal the engine keep running.
Engine misfire when under a bit of load until it is warm, after run smooth.
Thanks in advance for the reply.
Should I check for vacuum leak? Maybe the mixture enrichment don't work very well...
March 15, 2015
  Followup from the Pelican Staff: Could be many things. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. - Nick at Pelican Parts  
TSG Comments: I have a 1980 924 turbo. Up until a really long trip 3 days ago it cold started fine. All of a sudden it now struggles to fire up cold. Once started it starts fine. Any idea of what the issue may be?
March 8, 2015
  Followup from the Pelican Staff: I would guess it is a fuel delivery issue, but can't be sure until some items are checked.
When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
Carl Comments: Did any of the Porsche 924s come with a carb instead of CIS? Or will a carb form any other fit, I want to replace the CIS system entirely. I have a 1978 924.

Thanks, Carl
March 5, 2015
  Followup from the Pelican Staff: Not that I know of, the only ones I have even seen were conversion kit set ups. - Nick at Pelican Parts  
Brent Comments: I'm working on a 1979 928 for my uncle. The car sat for quite a while and had lots of gunk in the fuel tank, fuel lines, fuel distributor, injectors, everything. So far we have replaced all the lines, washed out the tank, replaced the pump, filter, rebuilt the fuel distributor, replaced the injectors and took apart the warm up regulator and cleaned it out. we also replaced pretty much all the vacuum lines in the engine bay. Also replaced the plugs, wires, cap, rotor, and cold start valve.

The issue with the car is that it is dumping fuel into the cylinder like crazy, to the point where it is soaking the plugs and blowing out of the exhaust. we have ordered the warm up regulator, but I am almost at my wits end.

Any thoughts?
February 20, 2015
  Followup from the Pelican Staff: Sounds like you have one of two issues. Stuck open injectors, or excessive fuel pressure. Check if the return line is restricted. - Nick at Pelican Parts  
Natee Comments: I just bought a 930 Turbo 3.3, the engine is running fine at idle. However, it is not smooth around 1,500 to 2,000 rpm in every gear. When the engine is warmer, it gets a little bit better but the problem is still there. It is worse when I turn the air conditioner on. Above 3,000 to 6,500 the engine runs very smoothly. What could be the problem?
December 19, 2014
  Followup from the Pelican Staff: Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders. - Nick at Pelican Parts  
Halen Comments: My 81 scirocco with the cis injection system will start great but it will die as soon as the starter disengages. Any thoughts on why this is happening?
November 21, 2014
  Followup from the Pelican Staff: Does it stay running if you hold the throttle open? - Nick at Pelican Parts  
Johnjohng Comments: Hi, I've just got a 1983 930 3.3 turbo, it was parked for awhile, started it up and it will sputter, driven it and there would be no power at all, I would smash the gas peddle all the way down and Feels like a 1969 vw, after 5-mins and building up some pressure, I would again hit the gas all the way down and wait a second and it would do a whip lash on my neck how fast it would go, stalled out right after, but again after starting it up it would sputter, it would take a wile after I press the gas peddle all the way down and just would patter, patter, and barley build up pressure like a bad plug, but it's all just done by the first owner, wires, cap, ect.... I've also noticed a vacuum hose with a small bolt into it? The turbo seems ok? But there again after it reaches over 30 m.p.h, it will spool up great, I am a newbe to this all, don't want to pay hundreds just to have a dealer look at it, any help on your professional option would be so greatful to me,

Thanks so much
John
Houston tx,

Car has 83k miles.
Don't know to much history on car as maintains fuel sys or tune up is all concerned,
November 20, 2014
  Followup from the Pelican Staff: I would start by checking the fuel quality. If it is poor from sitting, you will have your symptoms. - Nick at Pelican Parts  
TAF Comments: I have a 1977 930 with several mods including 964 web cams, Garretson intercooler, 1bar spring, SSI headers, diverter valve vented to atmosphere. CIS is stock. The car has developed an idle problem. Start ups are fine both cold and hot however, on cold starts, after about 60 seconds the idle goes rich and drops off and dies. Restart is slow. At full operating temp idle seems fine but sometimes runs up to 1200 to 2000 rpm with clutch pedal depressed. place the shifter in neutral, release the clutch and RPM settles back between 900 and 1000 rpm. Any thoughts?
November 16, 2014
  Followup from the Pelican Staff: The clutch release may be coincidence.

have you checked fuel pressure and volume? I would start there. Seems like it could be your issue. - Nick at Pelican Parts
 
rekay Comments: I have a 82 924 n/a anday it won't start and I replaced the fuel distributor and injectors and pumps and startake bUT dies it has white smoke in the throtle body is it over fueling idk but you smell Gas outide at the tail pipe
November 5, 2014
  Followup from the Pelican Staff: White smoke is likely coolant. I would pressure test the cooling system. If the system will not hold pressure and there are no external leaks the head gasket may be faulty.
- Nick at Pelican Parts
 
Ozone Comments: I just brought my 73 1/2 CIS injected 911 back to life after 4 years. Drained out gas and cleaned throttle body with spray. It fired up and after a bit of high revs, it "cleared" out. Took it for a drive and it "bucked" a bit, so I figured I would do an electrical tune up, plugs cap etc. It seemed as though the sensor plate was "stuck" so I carb cleaned it and lifted it up. Could I have broken something? Now the injector manifold sounds different, high pitched whine, and filled the cylinders with fuel! Help!
October 25, 2014
  Followup from the Pelican Staff: You may have damaged the CIS unit by forcing it up too high. Did the plate return the position it was in prior to you lifting it? - Nick at Pelican Parts  
Rennserv Comments: Is it possible for the airflow sensor plate to "knock", or bounce, at the top of its movement pattern under heavy fuel/air loading? I think I am hearing this in my CIS system on my 2.7 '77 911. I can replicate the noise manually by moving the lever and pushing the plate to the top of its range. Car seems to be running well, save for this sound. I could not find mention of this symptom anywhere else.
October 5, 2014
  Followup from the Pelican Staff: I have not seen that specific issue.

You may have a broken baffle or heat shield. Can you isolate the area of the noise? - Nick at Pelican Parts
 
Delorean Comments: The only things I have noticed is the supply fuel pressure fluctuates quite a bit. Between 70psi and 50psi and the fuel sensor flap starts vibrating heavily. Control pressure is steady at 50psi when hot.
September 6, 2014
  Followup from the Pelican Staff: It has to losing air or spark then. - Nick at Pelican Parts  
Delorean Comments: Yes it always starts immediately after
September 6, 2014
  Followup from the Pelican Staff: You're going to have to monitor some things to see what happens when it shuts off. Start by watching power to the ignition system and monitoring fuel pressure. - Nick at Pelican Parts  
Delorean Comments: I have an 81 dorean with the same system. I am having problems with it stalling under hard acceleration. I have replaced every part of the fuel system as well as had it adjusted by a professional in CIS. However it is still stalling. I can't seem to figure out why. Any suggestions to start? It seems to me like it is starving for fuel under load.
September 2, 2014
  Followup from the Pelican Staff: Does it always start right away after it stalls? - Nick at Pelican Parts  
BigJaye Comments: I have a '83 911sc put it in a shop just because it had set for 2 years and wanted to drive it no blowneng or bad trans just sat too long. I paid a shot $3700 and they still did not get it running threats to sazle it if I did not come to wig home on the way out he mentioned I should try a fuel pump relay. Gotta sue him understood but it almost cranksonce then just dies to a click and that iswith a new battery help.
August 17, 2014
  Followup from the Pelican Staff: I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and pressure fuel, volume and quality. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
tompo Comments: I have a '82 924 n/a CIS system. Car has been sat for a while and lots of issues. It sort of runs / fires now, but not fully. The throttle doesn't respond no rev's and ticks over very low, so its lacking air or fuel. I have increased the revs with 'starting gas', so I would say fuel. I have replace fuel distributor due to leak. Pump priming and fuel coming through. Injectors spray when air paddle manually moved - but the two will not work in sync. Air leak? Fuel pressure? have I missed a set-up/prime? Any advice pointers appreciated.
June 23, 2014
  Followup from the Pelican Staff: COuld be an adjustment issue. However, if it was fine, then started running poor, I don;t that being it. I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 
ian Comments: my 1982 911sc has been laid up for 2 yrs, when i started it this morning the engine just redlines ! throttle cable is free I don't know what to look at first.
June 15, 2014
  Followup from the Pelican Staff: Look for a large vacuum leak. Like the brake booster hose. - Nick at Pelican Parts  
robrizzo Comments: 1980 SC First start after 23 Years. List of what I did
1 replaced oil and filter
2 replaced frozen pump
3 drained and flushed tank and lines
4 check wires and plugs and whole ignition system. Works fine
5 removed filter and accum. made sure clean and clear.
removed injectors and soaked in Seafoam and injector cleaner they spray fine.
turn key on no fuel pump unless i jump it out. I can not keep it jumped out because it Hydrolocks motor.
Car has started but then dies. if jump too much gas and lots of white smoke and wont run smooth.
June 2, 2014
  Followup from the Pelican Staff: Does the relay have power on two terminals? You could be missing the control side power, it is fed from a fuse. I am trying to locate wiring for your vehicle, but am coming up short. - Nick at Pelican Parts  
MRM Comments: I have a 1986 911 turbo which I've had since it was new. For the last three years I left it parked in my garage. I recently had the car worked on including draing the gas and cleaning and replacing most of the fuel injection system. The car has 40,000 miles and is now running great but if I drive it till it gets to operating temperature then park it for a half hour or so it doesn't start easily or sometimes not at all till it cools off. The fuel pumps, accumulator, fuel distributors and injectors have been replaced. Any thought on the hard starting?
May 30, 2014
  Followup from the Pelican Staff: I would check the coolant temp sensor. If it is not functioning correctly, the engine may be difficult to start when hot. Other than that, you will have to check what is missing when it will not start. Check spark, fuel injector pulse and pressure fuel, volume and quality. - Nick at Pelican Parts  
Dan Comments: i have a 1978 , 911. I am fixing a fuel leak on my front lines . my question is , on the compression fittings . how do they come apart ? Are they threaded or snapped in place. if so , what is removal tool called or size. Thanks for help
May 11, 2014
  Followup from the Pelican Staff: If I remember correctly, they unscrew. I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
 
Zack Comments: From fd to wur I it has 73 psi cold is that to hi what could cause that and we have plenty of flow going back to the tank
April 21, 2014
  Followup from the Pelican Staff: Your test in the question seems incomplete. I think you are asking if your fuel pressure is too high. However, you never mentioned what vehicle you have. - Nick at Pelican Parts  
zack Comments: 1980 porsche cold start will idle but will not rev up have tryed to adj the wur and fuel mix at fd any ideas
April 18, 2014
  Followup from the Pelican Staff: I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 
drewski31 Comments: i have a 74 2.7 and it persistently idles high. i have tried to adjust the idle screw but that doesn't seem to work as it still revs back up. not crazy, just up 400 rpms.
March 31, 2014
  Followup from the Pelican Staff: I would check for vacuum leaks. - Nick at Pelican Parts  
luckysixtoe/ '67 912 Comments: I have a 1975 Carrera 2.7 litre with cis injection in my 912. I want to install a mild supercharger 6psibut am not sure if the stock fuel injection system is adequate. The '76 through '77 turbo engines use cis but I don't know what the differences between non turbo and turbo engine injection systems are. I assume there are differences when one engine makes 175hp and the other 260hp.
February 10, 2014
  Followup from the Pelican Staff: I would think you will have to increase fuel volume and pressure. Can you source parts from a turbo equipped engine? This may be the best bet. - Nick at Pelican Parts  
spoon Comments: 1985 911 turbo. engine mild surging on excel. set idle speed to 950, mixture set to specs. than try lean and than again rich. already found fuel pump inop and blown fuse to WUR.timing is right on. problem is not always there. T times has popped on excel.. any Ideas? need help..
December 5, 2013
  Followup from the Pelican Staff: This is a very confusing question--I really don't understand you, especially the abbreviations. How is the "fuel pump inop". Does it come back on by itself? Seems to me that is first order of business, to find out why the fuel pump is inoperative - Nick at Pelican Parts  
Rich Comments: Regarding the July 17,2013 problem from SCEAF3: Have you adjusted your ignition points lately?
November 29, 2013
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
 
Mike Comments: It bucks under normal driving conditions. It only occurs when I shift - probably because the rpm's drop. The engine is in time and the dwell is on. I was told by a mechanic the fuel pressure was good too. I am going to try an electronic ignition but is there anything else I can look at?
November 12, 2013
  Followup from the Pelican Staff: I would confirm fuel delivery is good. If you are attempting to diagnose this issue yourself, you will want to run the tests yourself. Otherwise you cannot have confidence of what is working and what is not.

if it falls on its face when shifting, I would start with fuel delivery. For example, does the vehicle has good volume and pressure when the problem is present. You may have an issue with the fuel pump or CIS unit. However, it is best to test these items to know for sure.- Nick at Pelican Parts
 
sharondpw Comments: Ok, the more I read the more confused I get. If the cold start valve depends on the microswitch and thermotine valve and the starter needs to be engaged, why have the microswitch at all? The thermotine will stop enrichment if engine warm and the CSV stops when starter cranking stops!
November 11, 2013
  Followup from the Pelican Staff: If I remember correctly, the microswitch is for reading throttle plate position. - Nick at Pelican Parts  
sharondpw Comments: I should add that the bucking is not because I can't drive a stick. The car jerks and bucks but if I get the revs high enough, it goes away.
November 10, 2013
  Followup from the Pelican Staff: Thanks, got it. - Nick at Pelican Parts  
sharondpw Comments: I have a 1974 911 and the car starts and isles well. Car drives well in first gear but when I shift to 2nd the car bucks. It seems like a lack of revs makes the car buck. Any thoughts?
November 10, 2013
  Followup from the Pelican Staff: Does it buck under a light load or normal or heavy accel? This could be due to an engine misfire, ignition or fuel delivery problem.- Nick at Pelican Parts  
danmanporscheman Comments: I have a 1986 porsche 930 turbo, will sputtering to a start, as well as a bouncing tach after a cold or warm startup,that lasts for about 10-15 minutes, then eventually returns to normal idle indicate a faulty WUR? ...it doesn't happen everytime, but usually happens more often than not, on start up. Also, if I set idle at 950, sometimes while driving, when comming to a stop, ie. engaging the clutch to put in neutral then slowing to a stop, the rpms drop, & it sputters to a stall. BUT after adjusting the idle to 1,000-1200 it won't stall.
October 30, 2013
  Followup from the Pelican Staff: I would perform a fuel delivery system test. Check fuel pressure, volume and quality. if your fuel pump is not working properly, it could cause the symptoms you are describing. - Nick at Pelican Parts  
911rick Comments: Had prob with the "jerking".. Would also see lights dimming and seat belt lights would flash.. Voltage regulator.. 1989 Carrera Cab
October 29, 2013
  Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it. - Nick at Pelican Parts  
sceaf3 Comments: My Porsche is possessed. It is a 1975 911 Carrera, stock 2.7 with stock CIS. I have had the following problem for about 2 years with no luck at curing it. There are times when the problem will not appear for days, other times it shows up one block down the street. It seems to show up more often when it gets hot, but will also do it to a lesser degree when only warm. The symptom is that it starts to jerk, lightly at first, sometimes so lightly that only I can feel
it. But I recognize it right away and know what is ultimately going to happen.
It may continue only lightly for the rest of the day. Eventually the jerking back and forth becomes violent then it either begins to backfire and then dies, or just acts
like it has run out of gas. When I say jerking, I mean it feels like the engine just quits but only momentarily. The jerking has no rhythmic cadence as it would with most ignition faults. At times it will crank right away after the engine finally dies; sometimes it takes a while to crank. One mechanic who started his career working on 1970s 911s thinks that it may be vapor locking. I don't see how a system that is under constant pressure can vapor lock when the engine is running. Further it can be present any any time. It gets worse as it gets hotter but not regularly enough to decide it is vapor lock. The car seems to run a little hot, but not excessively. It has a Mocal front oil cooler replacing the trombone. It gets up to 230-35 pretty quickly in 90+ degree Florida weather in town with the AC on. It cools of pretty quickly after getting on an open road and turning off the AC. Runs pretty consistently at 210-20 even on mild 82-85 degreesdays. All suspected electrical problems have been eliminated. Everything on the CIS system has been replaced or rebuilt from the fuel pump to the accumulator, to the warm up regulator, fuel injectors, gas tank replaced due to sediment build up, etc.
The mixture has been set and re-set. The only major part of the CIS system that has not be replaced or rebuilt is the fuel distributor. Because we found a good bit of sediment in the gas tank and replaced it I think some of the sediment could still be in the fuel distributor. The system was purged, but it seems to me it would not take much to make a fuel distributor malfunction. Question: Has vapor lock ever been a problem on this model? Do you think the symptoms could be caused by a malfunctioning fuel distributor? Do you have any other thoughts or suggestions for me
July 17, 2013
  Followup from the Pelican Staff: - It's unlikely vapor lock, due to the pressure the fuel is under, as you mentioned. Have you run a fuel pressure tester on it lately? If that tests normal, I have to say it but I think the fuel distributor is the likely culprit. Before replacing it, make sure to have the ignition tested on a scope to eliminate that as a possibility.  
Chris Comments: Do you sell used complete CIS injection systems? I wish to retrofit my Corvair with FI and would appreciate any advice regarding hoe to obtain a K-Jetronic system for a 6 cylinder engine.
January 20, 2013
  Followup from the Pelican Staff: No sorry we do not offer entire retrofit conversions. You should look to buy a unit that was fitted to an engine that closely matches you specs and we can supply you with most of the parts you need to get the system installed and working. - Nick at Pelican Parts  
tamlee Comments: I got 1973.5 911t 2.4L engine and has cis fuel injector system. My engine was broken a rod. now What is the best way to fix my car? buy 3.0L engine or 2.4L engine to replace.
January 20, 2012
  Followup from the Pelican Staff: A 2.4 liter will be a direct fit with no modifications. To upgrade to a 3.0 liter will require some modifications to get it to fit. - Nick at Pelican Parts  

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