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Additional Instructions for Testing Bosch CIS

Pelican Technical Article:

Additional Instructions for Testing Bosch CIS





Applicable Models:

Porsche 911 (1974-83)
Porsche 930 Turbo (1976-79)

Hot Tip:

Clean dirt off distributor cap

Performance Gain:

Better ignition and performance

Complementary Modification:

Replace fuel filter if needed.

Four pressure tests can be made with this tester: 

  1. Cold Control Pressure - engine cold, valve open
  2. Warm Control Pressure - engine warm, valve open
  3. Primary Pressure - engine cold or warm, valve closed (closed valve eliminates control pressure)
  4. Rest Pressure - engine warm, valve open

The CIS pressures shown in this book are for the warm control pressures. For pressures for tests A & C, consult the vehicle service manual, a Mitchell Fuel Injection manual, of Robert Bosch Service Guide booklet for Fuel Injection.

To make tests:

  1. For test "A" (above), the engine should be cold, standing several hours or overnight.
  1. Relieve fuel system pressure.
  1. Make sure fuel filter is not clogged. Replace if doubtful.
  1. Clean dirt off the fuel distributor cap.
  1. Referring to the typical CIS hookup diagram, hook up the tester between the fuel distributor and the control pressure regulator. The hose without the flow control valve should be connected to the center of the fuel distributor. The hose with the valve should be connected to the hose removed from the fuel distributor or connected directly to the control pressure regulator.
    1. CAUTION: hand tighten any adapters with the O-rings to avoid damage to O-rings.
    1. In a few cases, to get the right combination of threads to connect, the adapters may have to be piggy-backed.
  1. Reactivate fuel pump, start the engine and check for leaks.
  1. When the tester is connected, remove the air from the system
    1. If your tester has a release valve under the gauge, wrap a rag over the valve and depress button until the air is released. Do not do this over a hot engine or manifold.
    1. If your tester has a bleed-off valve, put the end of the bleed-off valve tubing in a fuel container and with fuel pump operating, bleed until air is removed.
    1. If your tester has none of the above, position the gauge downward as far as the hoses will allow with the gauge below the hoses and control valve. Operate fuel pump with the engine off. Open and close the control valve at least 5 times with the valve in the off and on position at least 12 seconds.
  1. When pressure stabilizes, read the gauge. If the Cold Control Pressure is not correct, the warm-up regulator may be at fault.
  1. If pressure is okay, run the pressure checks
    1. Warm Control Pressure and Rest Pressure must be measured with engine warm.
    2. Primary Pressure can be measured with engine cold or warm.
  1. Pressure range
    1. If pressures are not within the normal range on the control Pressure Warm test, try adjusting the fuel pressure regulator. If it cannot be adjusted to normal pressures, replace it unless the problem is as below (b)
    1. If the pressure is low with engine running and at idle, check to see if the voltage is at least 11.5V at the warm-up regulator plug contacts. If full voltage is available at the plug, then the warm-up regulator may need replacing.
  1. If the pressure is too low, test the fuel pump volume. Also, there may be a blockage in the supply line or leakage in the return line. If the system has none of these, the fuel system pressure needs adjustment. Consult the factory manual or fuel injection manual for the procedure.
  1. If Rest Pressure drops too quickly, check for leaks at O-rings and fuel line connections. If no external leaks, check for a leaking cold start valve of fuel injectors. If still no leaks there, leakage may be at the fuel pump check valve or at the O-ring on the relief valve in the fuel distributor. Repair or replace.
  1. If no problems can be found in the fuel injection system through pressure testing, fuel pump should be checked. For this, your tester should have a bleed-off valve and tubing. If you do not have one, it can be purchased from your tool supplier. With gauge hooked up to pressure test, put bleed-off tube into a fuel container of at least 2 quarts or 2 liters. Fuel flow in 30 seconds should be 1.5 - 2.0 pints or 3/4 - 1 liter. Turbo cars may have a volume of 20-25% more than non-turbo.
  1. Deactivate fuel pump and relieve fuel system pressure. With key off, put bleed-off tubing in a fuel can and press bleed-off valve. If your tester has no bleed-off valve assembly, wrap rags around connection and release slowly. A bleed-off assembly can be purchased from your tool supplier.
  1. Remove tester and reconnect all lines.
  1. Start engine and check for leaks.
  1. Remove fuel from all hoses. If fuel remains in gauge hose assembly, connect the smallest banjo bolt adapter into the quick coupler over a fuel container. Hold gauge above hose and fuel will flow into the fuel can.

[click to enlarge]



Comments and Suggestions:
Elvis Comments: Nick, following from your reply on my post dated 18Apr, I performed a couple of checks using the CIS pressure tester. Fuel system pressure @ 4.75 bar, injector opening @ 3 bar, no vacuum leak. All seems ok. Any other checks I should perform? To clarify I swapped out the original cams to a 964 profile. Timing is set as per new instructions from cam maker. I have a K&N filter and the fabspeed airbox.
April 26, 2016
  Followup from the Pelican Staff: If fuel pressure and timing is correct, you may have a back pressure issue. You can confirm by monitoring exhuast backpressure when the problem is present. You should have almost none, for your problem I would expect to see over 1+ PSI pretty quickly, then a higher as RPM increase.- Nick at Pelican Parts  
Elvis Comments: I have a 1978 911sc, which I recently swapped out to a 964 profile. Everything is timed to spec now. However I can't seem to push the car pass 3500 rpm at 4th and 5th gear no matter how much I press on the throttle. Have checked fuel distributor, CDI, fuel filter. All seemed to be in good order. Any other tips you may know of?
April 18, 2016
  Followup from the Pelican Staff: Start with the basic. What is fuel pressure and volume? What is exhaust back pressure? - Nick at Pelican Parts  
SteveB Comments: I have an '83 SC with CIS injection. The engine was disassembled, head bolts replaced, & reassembled. It will run, but poors gas through the system & out the exhaust...ALOT! Any ideas??
April 14, 2016
  Followup from the Pelican Staff: Sounds like the fuel distributor is allowing too much fuel to flow. First check that the fuel lines are routed correctly, then confirm fuel pressure isn't too high. If both are OK, the fuel distributor needs adjusting. - Nick at Pelican Parts  
Brian Comments: Nick, I have a Euro KR 16vw volkswagon. What is the reconended pressures cold/warm at the warmup regulator. Part number 0438140140. Thank you.
December 18, 2015
  Followup from the Pelican Staff: I don't have info on European models. I would grab a repair manual. It will have the procedure, special tools and pressure specs.
- Nick at Pelican Parts
magicmouse69 Comments: Looking to buy the potentiometer that goes on the side of the fuel distributor do you sell this or know where that can be bought? For audi gt coupe 86 je-jetteonic
April 30, 2015
  Followup from the Pelican Staff: If it is available we can get it. Usually, the entire sensor plate has to be replaced.
Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
em Comments: Where can I find the recommended CIS pressures for a 1982 911 SC 3.0 engine with serial #464D2733? Thanks
April 6, 2015
  Followup from the Pelican Staff: This is what I have:

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
- Nick at Pelican Parts
Anders Comments: I had a 3 liter engine installed in my 72 911. When trying to start the car, it starts and runs momentarily but the dies and refuses to start while running the starter. The same thing happens over and over again. Please help!
September 4, 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
koko Comments: Yes I can keep it running by pushing the air-flow sensor plate up at a considerable distance from the resting pointwhile pressing the throttle open. By manipulating both of these plates I can very the RPM from idle to max. As soon as I let go it dies :
Thanks for your timely response.
August 21, 2014
  Followup from the Pelican Staff: OK, there may be an issue with the sensor plate or throttle adjustment. I would start by checking fuel pressure to be sure it is OK, if low, it could cause the engine to stall at lower RPMs until the plate opening is increased. Then adjust the idle settings as needed. - Nick at Pelican Parts  
koko Comments: after rebuilding my '82 3.0 sc engine i can't get the engine to idle. it starts and dies. pressures are correct so is the timing. no air leaks or fuel pressure losses.
August 19, 2014
  Followup from the Pelican Staff: Can you keep then engine running by opening the throttle plate? - Nick at Pelican Parts  
vic gwee Comments: hi,i got 1 porsche sccis system when after warm start 10 or 15 minute, then can not start. can i know what the problem is? but i play abit air flow sensor then can start.
March 3, 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
profile Comments: I have no power at the warm up valve!! is there a fuse or something i should ber looking for?
January 11, 2013
  Followup from the Pelican Staff: I would grab a repair manual. It would have all the fuses listed as well as the wiring. - Nick at Pelican Parts  
Capt Surinder Comments: I am looking for a Fuel Volume Distributor Bosch NO 135 1905 6609 for BMW 3181 E21 1984 HELP Tks
August 27, 2012
  Followup from the Pelican Staff: Give our parts specialists a call: 1-888-280-7799 they will be able to help you find the right part. - Nick at Pelican Parts  
Mark Comments: I am a Porsche tech of more than 25 years and cold running misfires are generally caused by carbon buildup on the intake valves which can be cured by a walnut media blast.
July 27, 2012
  Followup from the Pelican Staff: - Sorry for the long delay in replying. We have recently added staff and are trying to get caught up. Thanks for writing!  
JamesG4381 Comments: Does anyone know what the pressures are supposed to be for the European version of the 82 911 Targa. Since horse power is different I am curios whether some of the pressures shouild be different.I just got my 911 and am having cold running issues. I replaced the O2 sensor and its better but still struggles cold with a lot of poping into the intake initially then missing untill runs normall temperature.I'm abouyt to try a full diag on the system and was curiou8s.It also backfires significantly during hard deceleration all the time.Seems like may be running rich
October 22, 2011
  Followup from the Pelican Staff: TEST RESPONSE2B+photo - Wayne at Pelican Parts
porsch problem Comments: i have problems whit my 88 911 porsch 3.2 wen the motor is cool runs good but wen is hot never start
please some body help me !!!
September 12, 2011
  Followup from the Pelican Staff: - Sorry for the long delay in replying. We have recently added staff and are trying to get caught up. Did you ever get it resolved? Does the engine crank normaly but won't start when hot? Or does it crank too slowly? If it cranks normally it may be an igntion components that fails when hot.  
koko Comments: My 76 911 has early 80s 3.0 . How can I Identify the year?
My real problem is starting. I use to press the air ventury until i felt resistance and heard a bucking sound. then the engine would start, hot or cold. now i cant feel resistance any more, just clicking of the fuel relay.

I thought it was the fuel pump but after removing, testing found it in good condition. After reinstallng the pump my trick pressing on the ventury worked again, but only once. Back to no resistance when i press the ventury. HELP!!
August 25, 2011
  Followup from the Pelican Staff: Models from 1977–1983 used a 3.0 liter.

I would fuel pressure to the CIS unit. The reisstance you felt may have been the fuel pressure on the back of the valve, now that fuel pressure may be missing, creating a lack of resistance. - Nick at Pelican Parts
Newbe Comments: Hi, I need to find fuel supply pressure and warm up regulator pressure control pressure for cold engine. I have a 1977 911S. I do have cis fuel gauge. Car starts cold then stalls and back fires intill warm , then runs great
January 8, 2011
  Followup from the Pelican Staff: CIS System Pressure: 4.5-5.0 bar

CIS Control Pressure (at idle speed):
warm-up regulator controlled: 3.6 +-20 bar
only fuel pump run: 2.9 +-20 bar - Nick at Pelican Parts
Targa Bob Comments: Step 13. According to C. Probst in Bosch Fuel Injection & Engine Management Bentley Publishers, Chapter 6 page 12 the delivery specs are .160 to .240 liters for 60 seconds. See Fig. 4-4 for diagram of procedure. Am I mistaken, this should be the same test setup. Delivery specs are so different.
September 29, 2010
  Followup from the Pelican Staff: I'm not 100% sure where the specs in thsi tech article came from. But I feel like both are OK. I always used a pint in 30 seconds, which is about the same as both. - Nick at Pelican Parts  
European_Rocc Comments: i don't think it should matter at that rate; based on manuals i have read about CIS, the engine can't use all of the gas the pump delivers anyway. The pumps just constantly return it to the gas tank hence the title
continuous injection system. I really doubt an ounce of a different is going to cause problems with your performance, unless you run the car at full pedal everywhere you go. So the answer is: Yes 44 ounces should be sufficient.
June 27, 2010
  Followup from the Pelican Staff: Actually, the name CIS (Continuous Injection System) doesn't refer to the recirculation of the fuel back to the tank - the MFI systems also did that as well. CIS refers to the fact that fuel is injected into the cylinders at a constant rate - they are not pulsed with respect to the position of the crank or camshafts. Even when the valves are closed, the system is still pumping fuel into the intake. It's not a very advanced system, although the modern Motronic fuel injection system that was introduced to the 911 afterwards also used continuous / pulsed injection. If you look at the wiring diagrams for the 1984-89 Carreras, you will see that each bank of injectors are electronically wired together. So, they do pulse in a metered fashion with respect to crank speed and throttle position, they too also dump fuel into the intake in a non-timed fashion, similar to the CIS cars. - Wayne at Pelican Parts  
Greg Comments: I recently did the fuel pump delivery test on my '78 5 speed 928 at the return line on the system pressure regulator that is part of the fuel distributor as outlined in the Bosch Fuel Injection and Engine Management publication. Shop manual calls for at least 1360cc = 45.9 ounces after 30 seconds-2 fuel pumps. I collected just about 44 ounces, is this sufficient considering I used a 7" hose with a banjo fitting and connected another 53" hosetotal 60" that ran up from the fuel distributor over the fender and into a container. I disconnected the 53" segnent of hose and lost some in the process also there was a seep at the fuel feed line which I have since tightened.Used a $12 watch with second hand for time. All things considered does 44 ounces seem sufficient? Any knowlegeable response is greatly appreciated. Greg Heinrichs
April 20, 2010
  Followup from the Pelican Staff: I wouldn't sweat the cost of your watch. :)

If you spilled some fuel, I would re-do the test. For example, fill the test hose with fuel and the bottom of your test container (measure or note the level you will fill it at), this will avoid a lag during the test. Then run your volume test and subtract the existing amount of fuel in the test container from your results. - Nick at Pelican Parts

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Page last updated: Sun 3/18/2018 02:20:51 AM