Documents published for owners of MFI automobiles are understood to be freely available. If you believe you own the copyright of anything listed below please accept my apologies and contact me immediately to have it pulled the site.
- MFI Pump detail
- MFI Regulator detail
- MFI Top diagram
- MFI Thermostat diagram
- MFI Fuel System diagram
- MFI System diagram
- MFI Air Filter diagram
- About MFI by Lee Rice (.pdf 580k)
- Adjusting MFI by Lee Rice (.pdf 382k)
- MFI Fuel Injector Maintenance (.pdf 70k)
- Bosch MFI Repair (zipped .pdf 4,556k)
- Bosch MFI Repair (more stuff) (.pdf 338k)
- Bosch MFI Storage instructions (soon)
- Bosch MFI Pump Test Instructions (soon)
- Check Measure and
Adjust (zipped .pdf 2,500k)
(Converted to PDF by Bruce Herrmann and Derek Murray)
- Fuel System (incl. MFI) Maintenance (soon)
- Tuning Instructions (soon)
- Mercedes MFI Adjustment Instructions (soon)
- Contacts for MFI service
- Replacing a pump
- Pump maintenance
- Setting idle mixture & throttle body maintenance
- Cold start enrichment hoses and connections
- MFI Vacuum system
- MFI Adjustment basics
- MFI running rich at high rpms
- MFI Cold start problem
- MFI thermostat R & R
- Re: Pump timing
- Awesome overview from Rennsport
- MFI fixed (72 911E)
- MFI system matching
- Ultrasonic cleaning of MFI injectors
- Disconnecting MFI Throttle Linkages
- Carerra RS / MFI info needed
- MFI cold start problem?
- Sloppy (wet) exhaust port...
- MFI Misses (Was Re: engine miss when engine is warm)
- Missing when warm MFI problems
- MFI problems
- MFI problems I
- MFI problems II
Start motor and warm to operating temperature (180°C).
On the MFI housing behind the thermostat is a small triangular cover plate.
Remove this inspection plate and observe if the thermostat rod is pushing against the cam-shaped lever. This lever should not be able to move back further. (Use a small angled screw driver or similar to gently check the there is no movement). If there is, continue as below.
To remove the bottom screw on the thermostat cap, grab your air cleaner with your fingers while placing your thumb on the thermostat cap, remove top screw (cap is spring loaded).
Remove cap, set aside, (don't lose cap gasket, mine was broken so I made another
one -- this thing will not work without the gasket, it's also a spacer).
Draw out the rod with elements -- I would not take them off if it works!!
(There are 25 pairs of expansion elements (mounted like cymbals) fitted first, followed by three slightly larger flat washers).
Clean with carby spray cleaner, set safely aside.
Remove bottom screw on thermostat housing (kind of hard to get at), hold on to housing,
remove top screw, remove housing.
You should have a cross shaped gasket with a hole in the middle, and a metal spacer.
Should also have a small rubber "o" ring type gasket in the flange on injection pump.
Clean them up using parts cleaner or carby cleaner.
Note: Many of these are suggestions are copied from various newsgroups. I have removed the names to protect the innocent. Let me know if you recognize your work and want credit listed here.
MFI Pump part numbers:
911SC/RS 3ltr = ???
911S = 0408 126 009
911E = 0408 126 010
911T = Carbs
Pacific Fuel Injection (Gus Pfister)
|Suite B, 153 Utah Av|
South San Francisco, CA
Tel. 650-588 8880
Jerry Fairchild Industries (Robert Turner)
|5242 Westside Rd|
Redding, CA 96001
Tel. 530-241 1592
Walz Diesel Fuel Injection (Norbert Schuller)
Tel. 02-9755 1422
Eurometrix (throttle body rebuilder)
228 Boston Rd
|Groton, MA 01450|
Tel. 978- 448 2557 (Matt Blast )
Phil Sumich (throttle body rebuilder)
Tel. 07-3390 8133
|Super Tec (throttle body rebuilder)|
|Tel. 714-429 1863|
I just took the plunge and replaced my MFI pump with another that I am hoping has an "S" cam in it. The car pulls stronger now, so it must be something other then "T".
Very important, rotate the engine to TDC of #4 piston (I full rotation past TDC of #1 piston) then another 40 degrees (there should be a mark on the main pulley). Then use a mirror to check the MFI pump to ensure the small mark on the pulley is lined up with the mark on the pump body.
Removing the pump is the easy part, except for 1 bolt that mounts the pump to the engine. This "devil" bolt is on the left front side and is covered by injector lines. To make it more fun using a socket extension is difficult because it doesn't quite fit with the injector stacks. After 2 hours getting that bolt out the rest followed including the fuel lines and oil tubes in about 30 minutes. Pick up some 1/2" and 1/4" plastic caps from the hardware store to cap the unit (especially the oil in tube, otherwise a bunch of oil will leak as you tilt the unit to pull it out). Lift and pull out the unit. Be careful not to let the drive belt fall off the cam pulley. While unbolting the unit I actually lost a bolt and it fell under the belt down to the cam pulley. I was able to fish it out using a screwdriver from the outside left hand side of the car (don't leave it down there).
Installing the new unit is even more fun. Fill the new pump with 300cc of engine oil (and cap with one of those 1/2" caps until you are ready to attach the oil hose). Make sure the crank hasn't moved. Compare the two pumps and make sure the teeth are absolutely identical when the marks a lined up. If not loosen the gear and rotate. When sliding the unit in place it is easier to make sure the belt is on the lower part of the pump and pulling it over the top as you complete the installation. Make sure the pump pulley mark is still lined up with the mark on the pump. Also make sure the belt fits cleanly in the teeth of the pulley without rotating it from the marks. Screw everything back on in reverse of the install process. Good luck with the devil bolt... I have yet to put it back in mine. :)
Bosch mechanical injection pumps are complex mechanical devices with many intricate and delicate internal components. Due care should be exercised when handling or working on these pumps as the internal parts are often very hard to replace and very expensive to buy.
Therefore it is essential that your Porsche's injection pump is well maintained to provide the excellent performance and durability that came with it from new. A well tuned injection pump will provide far better fuel delivery to the engine than any carburetor setup and work well in all conditions and engine specifications. The injection system was first developed for the Porsche racecars for just this reason. Keeping your injection pump clean and maintained to original specification will provide years of trouble-free motoring for you and your Porsche.
There are actually two distinct parts two the Bosch mechanical injection pump -- the pump and the regulator. The pump section contains the camshaft, the fuel galleries and the six pistons and associated connections and the control rack. The regulator (at the rear, direction of car motion) contains all the control devices for the thermostat, enrichment, leaning, idling and power ranges, counterweighted space cam on the end of the camshaft, and various levers and adjustment screws to control the metering of fuel supply to the injectors.
The following points should be noted with respect to the mechanical injection pumps.
Cleanliness -- always keep the area around the pump housing free of debris, oil and moisture. Look regularly for oil leaks from the various oil lines and cover plates on the pump housing, examining fuel lines and junctions for fuel seepage.
Oil -- regular oil changes (with filter) will provide your pump with a regular "cleaning" of oil in the cam and piston galleries, reducing friction on moving parts. Less gumming up is also the result.
Fuel -- the same applies for the fuel filter and fuel quality.
Checks -- does the control rack move freely? Remove the plastic plug and the driven end of the pump, insert the blunt end of a biro and gently push into the pump and release pressure. The biro should move back to the original position. If not, a gummed up pump is what you have. Thermostat not working? Check the hose from the heat exchanger to the top front of the pump. It must be in good condition and unobstructed. Thermostat elements may also need cleaning. Examine the drive belt for wear, and also the drive gears on the pump and end of camshaft. Seal can also leak. Other components related to the injection, which may fail, are the rpm transducer, cold start solenoid, microswitch and fuel pump. The vacuum system from the distributor and lines may also leak.
Tune-up -- if your car is not tuned properly, your pump will never work at its full potential. An out of tune, worn out engine will force the pump's various elements to overcompensate for the engine's shortcomings, resulting in overly rich running, poor idling, fuel in the oil, poor acceleration etc. Before doing any fuel injection service, always ensure that your car has proper timing, good compression, correct fuel pressure, distributor, ignition and vacuum pressure. A worn engine will allow carbon buildup in the oil to travel throughout the pump. Carbon can also build up in the air bleed screw shafts, making the task of balancing the throttle valves almost impossible. Correlation of the throttle bodies (linkages) is essential.
Moisture -- a major source of problems in the pumps is the ingestion of moisture, particularly in cool, wet climates where the car is not frequently used. This causes corrosion of the working parts and eventually seizing of the pump. By regularly spraying around the pump with WD40 or RP7, moisture will be largely eliminated. Also regular cranking over of the engine or rotation of the pump drive shaft will maintain lubrication of parts.
Storage -- pumps which have been removed for the car should be flushed and sealed prior to storage. Kerosene is suitable for flushing out the pump and regulator housing. Pour in through the fuel and oil inlets while rotating the drive shaft (cam) clockwise and turning upside down. You may also remove the side cover and governor cover to add more kerosene. Wipe down housing with a clean lint-free cloth when finished. The pump and governor must now be treated with calibration fluid in order to preserve the delicate internal parts. Calibration fluid (eg. Bosch # 5 701 301 725 or equivalent) is only available from specialist fuel injection shops and is expensive. About 1/2 litre should be sufficient. Repeat the sequence as per the kerosene cleaning and drain well. Replace all covers and ensure a coating of calibration fluid remains on the outer casing as well. All hose and fuel line vents should be plugged (plugs available from fuel injection shops) and the pump stored in a sealed plastic bag in a moist free environment at room temperature. Quarterly inspection and clockwise rotation of the drive shaft cam is advisable.
Pump seizure -- MFI pumps which have been allowed to stand idle for long periods with oil and fuel in side them often suffer from binding or sticking control racks and gumming up of fuel galleries, as well as possible seizing of internal components of the pump and regulator. To overhaul such pumps, fill fuel inlet with carburetor cleaner (or methyl alcohol), Remove plastic plug above driving cog (back of pump housing) and insert the blunt end of a plastic biro or similar non-metallic object into the hole to contact the control rack. Using slight pressure, gently push against the control rack while turning the drive cog clockwise. This is best done if the MFI pump is clamped to a work bench. Push and release the biro as you rotate the cog. Repeat this procedure until the rack moves freely with the MFI camshaft using very little pressure on the biro. You may have to add more cleaning fluid and repeat the steps several times. If, after several attempts, the control rack is still stuck, it is time to send the pump off for a rebuild.
The above procedure can also be performed with the MFI pump still mounted on the Porsche. However, prior to removal of the drive belt for the pump, the injection timing must be set for the end of delivery stroke (F-E mark on the crankshaft pulley) in relation to the set mark on the pump drive cog shaft. To do this, bring piston 1 to TDC, rotate fully 360° (1 revolution of the crankshaft pulley), followed by a 40° turn to reach the F-E mark and the top mark on the fan housing above the crankshaft pulley. Using a mirror and torch, examine the position of the drive cog and shaft on the back of the injection pump. There should be a notch mark showing at the top position of this shaft (a matching 12 o'clock mark on the housing).
The drive belt can now be removed. This is easily done if the pump housing is loosened on its mounting bolts and gently slid sideways to the left. This releases tension on the bent and it can be slid off the drive cog. Place a cloth under the fuel inlet banjo joint and undo. (Caution -- avoid any sparks or flames, keep a fire extinguisher handy!!). Once the fuel inlet pipe is exposed, you can now proceed as above with carburetor cleaner and try to gain movement in the control rack etc. Reinstall the hoses, belt and pump mounting in reverse of above. Remember to keep the notch mark on the drive cog shaft at 12 o'clock on the pump. Check the belt's tension with finger pressure -- there should be 6-8 mm movement in the center of the belt travel. Check all fuel hoses and lines for leaks prior to starting engine.
When attempting any work on the mechanical injection, it is well advised that you obtain a copy of the Porsche Factory manual on MFI and read it thoroughly before attempting any repairs. They stress the importance of three words: stop think repair! Your Porsche's engine will need to be well tuned and have good compression for the pump to perform properly. Only after you have checked all components of the ignition, timing, fuel system, wiring, vacuum and oil supply should you proceed with investigation of the MFI pump, the internals of which are best left to the experts. <TOP>
It is assumed that your throttle bodies have been cleaned and intakes (throttle plate, air mixture and vacuum) are "surgically" clean. Your throttle bushes should also have no significant wear. Regarding idle mixture tune-up, first turn the air correction screws on the throttle bodies fully closed, then back out exactly 21/2 turns. Then adjust the throttle stops by removing all the linkages and, one at a time, loosening each throttle bolt locking nut. Lightly push the throttle plate towards the fully closed position. Turn the throttle stop bolt to allow the throttle plate to close completely. When you get to the point where you have almost removed the bolt, the throttle plate will stick shut. Now screw the throttle bolt back to the point where the throttle plate no longer sticks shut. (This is rather critical as the throttle plate can be closed too far and stick, as engine temps increase and alter clearances). Now that you have the throttle stop bolt set to just keep the throttle plate from sticking, screw the throttle stop bolt another 3/4 turn in the direction that opens the plate. Check for free play by pushing lightly toward the stop. If all is OK, secure with the locking nut and repeat on remaining 5 throttles.
At this point the engine should start and run, but idle will be slow. Run for a while (until engine oil temp. is about 180 degrees +), then shut down and wait 15 mins for heat expansion, then restart engine.
Check each throttle with an air flow synchronizer to find the throttle with the lowest air flow. Adjust throttle stop bolt on this throttle to allow more air through throttle plate. Note: NEVER adjust the throttle plate for less air (closing the plate)!! Then adjust all six throttles up to identical air flow. Idle speed should now be close to spec. (circa 900rpm). Note that bad plugs, timing, MFI pump adjustment will affect these settings, so make sure all is well before attempting this balancing.
Next, with engine still running, adjust and reinstall the four throttle valve connecting levers to just keep the throttle arms on the stop bolts without changing the idle rpm. L & R throttle valve push rods should be as close as possible to 149.5mm and reinstalled. Car should now idle but idle mixture should be now checked.
Normally if the idle speed is low, you must determine whether the engine needs more fuel or air. There is an easy way to check this. Remove the injection pump control rod at the cross shaft end (the large metal tube linking both throttle bodies). Leave the other end attached to the MFI pump. Check all throttles are still at their idle stops, then very slightly push the control rod open. This will inject more fuel into the engine.
Does the engine speed up? This means the pump is set too lean. Does the engine slow down and puff a little black smoke? This means the pump is set too rich. At perfect adjustment, pushing slightly on the control rod will cause the engine to initially increase revs a little the rapidly decrease. The MFI pump is adjusted @ 1000rpm for basic rich/lean with the main enrichment. Idle speed is adjusted with the idle enrichment and is only effective below 1000rpm.
Fine tuning can be achieved by turning all six air correction screws very slightly (1/16 turn for example) then rechecking with your air synchronizer to be sure they are all the same. Then recheck all linkages are lightly tight and ball sockets have Bosch ignition grease in them. Finally, check throttle pedal goes all the way down together with the MFI pump being at full throttle. <TOP>
Ensure these small hoses are not leaking and in good condition. Always use the proper FI hose clamps (i.e. do not use the slotted worm drive clamps as these cut into the hose over time). The tiny plastic T-junctions and elbows mounted on the sides of the throttle body trumpets should be tight and look for cracks if bent out of shape. Treat with care as these are not replaceable I believe!! (Also check your vacuum hoses and junctions periodically). <TOP>
Where and what are the adjustments I can make on the good old Bosch MFI? I have a 1972 911T that is running way to rich..Black smoke from the pipe...I'm sure the MFI pump needs a rebuild..The car sat for 9 years before I took over as caretaker...I've had the pump apart and have only a really basic understanding of how it works, but I need an even more basic understanding...such as what are the base lines I should be shooting for...
2.4 Ts never ran all that well to begin with, tending to be too fat anyway, and getting richer with age. The MFI training I received from Porsche/Audi Pacific involved a WEEK of classroom work, a full day of which was on the road performing the adjustment procedures. You MUST have a thorough understanding of both the operation and the adjustment procedures, as well as a small assortment of special tools including a gauge for the pump rod, a set of protractors, and a couple of screw turning tools, as well as a CO/HC tester that you can carry in a moving car.
You MUST have the engine in a PERFECT state of tune, with the plugs (either conventional or the special platinum's) at exactly the correct gap, the valves at EXACTLY .004", the dwell and timing right on the money, and the correct octane gasoline.
Then, and only then, can the adjustment be done. The warm up device must be cleaned and adjusted and the air supply feeding it must be adequate before adjusting the idle CO. After getting the idle CO right, the part load screw is adjusted. It CANNOT be done correctly without the portable CO machine, as it is set with the car moving, the properly adjusted hand throttle pulled up, in 2nd gear, and usually with the brakes lightly on. After the part load is set, you'll probably have to go back and reset the idle settings, and then the part load again. It may take several fine adjustments to get it to run right, and only then if the pump is in good condition.
I've done a lot of these, and I have a few friends in the business who have done them too, and I think any expert will tell you that this is not a job to be undertaken by the untrained nor those unfamiliar with the system. Remember, these things are, at a minimum, 26 years old, and guys who received the training have reached or are near the end of their careers, and most haven't touched one in a long time.
There are guys, including myself, who have put these into a 914-6, and the nightmare is worse. You can't access the adjusters in the car. I had mine preset by the guy who rebuilt it, and the engine was fresh. Luck was with us, and it is within tolerances for the moment. Wear may cause us untold grief. Good luck, and find someone who knows what he's doing, it'll be the best thing in the long run.
As I understand it, when the engine goes to idle, the vacuum ports on cyls. 1 and 4 builds up and "retards" the ignition thru the "vacuum dashpot" (5deg.).
I have a 72T with MFI that I've spent $1200 on rebuild, and I just found out that the "dashpot" is bad causing my idle to wander making some very strange noises. The reason I know this is I changed over the "dashpot" with an old one (had to drill out 1 mounting hole to get it to fit) and all the "pinging, clunking, stumbling, and ticking" is almost gone. I noticed that the one I removed was very easy to move the arm back and forth. (seemed sloppy)
> Emissions niceties aside, what happens if I plug the line and the vacuum pot on the distributor?
What happens on mine is the timing changes from "5deg.ATDC" to about "5deg.BTDC". I guess this is where the "advance" comes in, because when the throttle plates open, the "dashpot" loses vacuum, and the "centrifugal" advance takes over. When the throttle plates close, vacuum builds and the timing is "retarded" again to "5deg. After TDC".
Hey, I could be all wrong on this, because there's some confusion as to what some call "retard" and "advance".
I also have seen this problem (MFI running rich over 4,000rpm). I own a 72 911E with MFI, and I found that the thermostat on the rear of the injection pump can get dirty/carboned up over time, and will hang up forcing the rack into an over rich condition constantly.
You can remove this unit and disassemble it and clean it out, maybe some light sanding of the inside of the housing will be required but you can check the operation by measuring the travel of the actuating rod cold and then hook up a hair dryer (blower type) to the inlet hose and check to see if the little expansion disks pull the rod into the thermostat housing (leaner) as it is warmed. This rod must retract about 3/16" or so to lean out the rack. Also make sure that the rack is free to move back to idle position it should not bind, otherwise the rack is defective. I hope this helps - this worked on mine and seems to be common on these older cars. <TOP>
I have a '72 911E Targa with mechanical fuel injection.
It will start right up, but if I try to give it any gas it will loose power and stall. If I let it idle for 5-10 minutes it runs fine.
I don't know how you lived with it like that for more than a season. You should get the Bosch/Porsche MFI book "tune, test, adjust" or whatever it's called. You need to start at the beginning like the book says and check your ignition, compression, and other things and make sure they are right before you mess with the injection.
Then you might want to start with cleaning out the disks in the warm-up regulator by removing it and BEING VERY CAREFUL not to change the order of the disks which are not all the same.
You should also clean out the idle air passages on each intake. You can do it by removing the adjustment screw (count how many turns it is from closed first so you can re-install it). Then spray some carb cleaner down the hole and clean it out with a long pipe cleaner. The pipe cleaner will be REALLY dirty from carbon. Also clean the needle on the adjusting screw.
You can check for vacuum leaks with the car idling by spraying that carb cleaner around the base of the intake stacks -- if you hit a leak the engine RPM will change. Maybe you can check for leaks on the head this way too by spraying through the ducting.
Also check the pump timing which will require a mirror to see the timing mark on the back of the pump. I hear it's not that critical but couldn't hurt.
After fixing all these wear items, if it still runs bad you can then do the adjustments -- throttle linkage lengths, butterfly valve stops, pump vs. butterfly correlation, etc. Then you can set the part throttle and finally idle mixtures. Bob Spindel built a neat pipe with an O2 sensor which clamps onto your muffler and you read the voltage with a digital volt meter. It works good for the part throttle adjustment. I have an article I accumulated about using an O2 sensor for tuning if anyone is interested. <TOP>
First, check that your thermostat is working correctly:
If you need to clean out the thermostat I would do it this way:
Next, hold thermostat housing, install rod with elements, spring seat, spring, and compress cap with your thumb, install screws.
Check for movement on thermostat rod...about 3/16" (4.75mm) or so..
Now reinstall thermostat.
Also, about adjusting the pump timing... In my newsgroup wanderings I read two posts at different times. In both posts, they said that the Porsche factory racers found that they could detect no difference in engine performance, no matter how the timing was set. I haven't noticed any difference myself in the adjustment, but I still set it anyway. Just a little tidbit I wanted to pass on. -Hans Achter <TOP>
From Rennsport (Visit for more great performance information)
Bosch Mechanical Fuel Injection is a splendid, if not inexpensive, performance induction system. It was used on the 911S and 911E from 69 to 73 as well as the 73 Carrera RS. Porsche used various types of MFI on factory racing cars from 67 to 84. This is a very complicated fuel delivery system that, if set up properly and in good condition, makes excellent power and throttle response.
The trouble is, few people anymore possess the necessary knowledge to make these systems run well and Bosch has little documentation available for the owner. Pacific Fuel Injection and Eurometrix are two of the most reputable re-builders of injection pumps and throttle bodies.
Injection pumps can be recalibrated to almost any engine size and camshaft. 2.7 RS-spec engines equipped with these systems continue to be quite popular since the requisite space cam for the pump is still available. Eurometrix can enlarge the throttle bodies to 40mm for larger engines as well. The larger plastic intake stacks as used on the "S" and Carrera RS engines are still available from Porsche as this is written.
Tall butterfly throttle stacks from the 73 2.8 RSR and 911 SC/RS are one of the good upgrades for engines used for racing purposes. These 50mm throttles work quite well for 3.0 litre and larger racing engines. Another upgrade to consider are the RSR throttle slides from the 74 3.0 RSR. These are being re-manufactured by Andial for racers as well as restorers. Other aftermarket throttle slides and fuel rails are available for the 3-bolt flanges used on 3.6-3.8 litre engines. You can even fit excellent quality aircleaners to these throttle assemblies. Typically, FI pumps used for racing are recalibrated to RSR-spec and the idle-cutoff solenoid is removed.
The early FI pumps are better suited for the RSR modification and the later pumps used on the 2.4 litre engines are better candidates for an RS-type upgrade.
Date: Thu, 5 Aug 1999 22:11:1
I have the same car, and have dealt with the MFI quite a bit. Bruce Abbott certainly has some good advice; it will take some time to get familiar with it.
You might get some help from my experiences:
(When I had the MFI pump rebuilt and reinstalled it,
the engine still ran like trash. There was still spark, and I could get a timing
light to work, so I never suspected the coil. After lots of frustration, I finally
noticed that the timing light would intermittently wink out when I revved the
engine). It's easy to check the coil with a multimeter (see Haynes manual.)
It's "chock full of info" on MFI! He'll
soon be posting the Porsche factory MFI adjustment manual, called the
73 911E Targa
From: Matt Beaubien <firstname.lastname@example.org>
Date: Wed, 11 Aug 1999 01:48:52 -0600
I'd like to thank everyone who sent me suggestions on what
was wrong with the MFI on my '73 911E. A few discoveries have been made and thought
I'd share them with everyone.
My cold start problem was in fact electrical. I ended
up removing the electrical panel in the rear and cleaning every single electrical
connection with contact cleaner and a brass-wire brush. She fired right up after
reinstalling the panel.
Quite a few people suggested that my poor part throttle
running and missing above 6k RPM may be a supply problem due to rust clogging the screen,
lines, filter etc. I didn't really feel that fuel supply was a problem as it was
fine at 5000 rpm at WOT.
I did some more investigating in the thermostat operation
on the regulator. I removed the top access port to get a better idea on how it
worked. It seemed that the thermostat never really moved that much. I levered
the assembly with the engine running, and was able to see black
smoke for the first time. I then operated the
throttle a couple times and noticed much better response than before.
To make a long story short, I started removing pairs of
discs from the thermostat. I removed one or two pair at a time but it didn't make
much of a difference. I then removed a whole bunch (~ half) and it seemed just
right. Took it for a spin and it pulled to 7k+ RPM in the first
three gears, without missing at all. Perfect!
This allowed me to go to a track the next day for a lapping session to get acquainted with
the physics of 911's.
It then started to miss again occasionally at part
throttle. This time it was a rich-miss. I could tell because giving a little
more throttle opening would make it stop. When it was lean, more throttle would just
make it worse. I'm now tinkering with finding the right number of washers to get it
running properly. I'm thinking of threading the thermostat cap to allow me to adjust
the preload quickly and easily.
(It seems that the spring or whatever in the regulator that
presses against the thermostat is not strong enough. Removing discs reduces the load
required to get enrichment happening).
For those of you that have had your MFI systems overhauled,
can you let me know how much to expect money wise? Private or public emails are
FWIW, my engine only pumps 135 psi on a compression gauge and burns a noticeable amount of oil. However, I was able to hit 6500 RPM in 5th which equates to 143 MPH (S+ numbers, no?). This was with the sunroof open and it was still pulling a bit. I have an RS-esque air dam and a duck tail which may reduce the drag a bit.
What a fun car...
'72 911 E
From: email@example.com (Peter Cowper)
Date: Fri, 20 Aug 1999 23:13:19 -0700 (PDT)
1974 911 . . . (with a fresh 2.4 S engine under the
bench waiting for 2003 when my car drops off the California Smog Roles!)
From: Terri & Marko <firstname.lastname@example.org>
Date: Thu, 21 Oct 1999 17:21:29 -0400
I recently asked listers if they had any luck using
this approach,aparently no one did -- so I
thought I'd try various techniques/chemicals...after many failures I won!!!!!
So, here is what worked for me. I used a 1 litre ultrasonic cleaner (large jewelers or graphic type) -- must be capable of heating solution to 150°+ F.
The solutions are simple and available at any hardware store... mix 1/2 turpentine + 1/4paint remover + 1/4 acetone, bring to temp.150°+ .
Soak injectors vertically for 2 hrs. Invert and soak for 2 hrs. Lie flat (roll back/forth) for 1hr.
The screens will be perfectly clean (there will be a small
amount of residue on bottom of
I cleaned same and repeated process -- IT RUNS
FANTASTIC!! You will have to lean the mixture on the pump behind the shroud
approx.3-4 turns or to your liking respectfully.
From: Bob Spindel <email@example.com>
Date: Mon, 25 Oct 1999 11:13:45 -0700
The sockets are made to pop off the
balls. Just wedge a large screwdriver blade between the ball and socket and twist,
or use an open-end 10mm spanner in a similar manner.
The length of only one rod is critical:
the rod between the MFI pump and the accelerator linkage. It should be 11.4 cm +/- a
few 1/10th millimeters from balljoint centre to centre. With that one set right, the
lengths of all the others fall into place.
Essentially, you adjust the length of
all the rods so that the butterflies are closed and each is just resting on it's
stop. The "correlation" will then be right. You don't need the
'73 911T (being restored)
Date: Wed, 27 Oct 1999 11:15:07 EDT
That number is the correct pump for a 2.7RS. They are
0408 126 XXX :
>> I also have the part number for the stack
(911.110.312.1R). Does that look consistent with an RS? <<
That # is not in the MFI book, it would be in the factory
parts book but I have that at home so can not check. The S and RS have bigger stacks
than the T and E, they should be the same as your '73S.
My '72S stacks had "S" written on them with
yellow grease pencil at the Factory I think (wonder if the concours guys check for that?).
>> Also, a more basic question, does the
Carrera RS have different stacks than a '73 S, how about throttle plates? There
seems to be a lot in common between the '73S and the '73RS so far. <<
Yes, they are almost the same engines. Only real
difference is space cam in MFI pump, and
pistons/cylinders. However the MFI book says that the
RS features "throttle valve casing with enlarged bypass bores for idling air;
recognizable by Solex part number on front surface".
So I guess the throttle valves are slightly different,
though it should be easy to bore out the S idle air passes a bit if idle is too low.
Good luck, sounds like you are putting MFI back on your
From: Mike Piera
>> I have a '72 911E Targa with
mechanical fuel injection. It will start right up, but if I try to give it any
gas it will lose power and stall. If I let it idle for 5-10 minutes it runs fine.<<
You can check for vacuum leaks with the car idling by spraying that carb cleaner around the base of the intake stacks -- if you hit a leak the engine RPM will change. Maybe you can check for leaks on the head this way too by spraying through the ducting.
Also check the pump timing, which
will require a mirror to see the timing mark on the back of the pump. I hear it's not that
critical but couldn't hurt. After fixing all these wear items, if it still runs bad
you can then do the adjustments -- throttle linkage lengths, butterfly valve stops,
pump vs. butterfly correlation, etc. Then you can set the part throttle and finally
From: Josh Pinkert <firstname.lastname@example.org>
Last night I pulled my heat exchangers so that I could
rotate my motor on the stand and have better access to the underside of my motor (cleaning
time!!!). It was a piece of cake... judiciously used PB Blaster on the bolts and
they came right off (although the muffler bolts were really rusty).
Upon looking at the exhaust ports, all of them were
uniformly caked with a dry soot, except for #2. Before I dropped the motor, I had
replaced the plugs, cap, and rotor and after subsequent test drives (and an examination of
new and old plugs) I concluded that plug #2 was fouling. Now that I have a chance to
look at the exhaust port for #2, I see that it's all wet.
My question is... is there an easy way to tell if it's oil
versus fuel? If it is fuel, I'm not worried. Just retune it. If it's
oil, then I'll have some problems to deal with. How difficult is it to pull just one
cylinder? It would require pulling the head from that side, so I'm looking at a good
investment in tools, plus I'll have to re-time the cams, right?
Josh Pinkert - '72 911T
From: Bob Spindel <email@example.com>
Date: Thu, 23 Mar 2000 13:52:25 -0800
The through-the-stack popping at idle is reduced mostly be getting the throttle linkages adjusted correctly. If you're off even a teensy bit on one stack -- pop pop! A good way to go about it is with a warm engine at idle, start popping (bad word!) off the links, checking to make sure they are adjusted so as to present no preload to their respective butterflies. This includes the link to the MFI pump itself (which should be exactly 11.4cm, ball-to-ball, this is critical) and the main link from each set of stacks to the accelerator rod.
The backfiring-through-the-exhaust can be minimized by adjusting the MFI pump for part load adjustment. A simple way to do it is lean the pump out (clockwise, I think) a lot. Get it to the point where it is so lean it idles poorly, and backfires like a banshee when you let up on the accelerator at speed. No need for walls here, you'll hear it if it's lean enough. Then start enrichening it a few clicks at a time until it idles nicely again, and doesn't backfire, and allows smooth acceleration through the 2500-3500 rpm range. All three of these will happen at the same setting. The switch from way too lean to just about perfect occurs over a very few clicks -- maybe 3 or so.
you do need something to allow you to determine how much
air is being drawn in. I use a device called a Unisyn, which has been around
forever. I'm not sure what they cost these days, but I'd be surprised if they were
more than $25 or $30 (although they're probably worth $10). There are all sorts of
fancy tools available. I've seen some with gauges on their faces that
cost nearly $100, but they are big time overkill. The
Unisyn just has a tube with a little ball in it that rides higher or lower depending on
the air flow. One just adjusts the bleed screws until the ball rides at the same
level for each cylinder. The bleed screw adjustment is pretty fine in
that it takes a fairly whopping adjustment to make much
change. With them all at 3 turns out you're probably very close, even pretty equal
on most, but usually there will be one or two cylinders that are off enough to start
popping through the stacks.
The procedure of taking a reading in all six and then finding the mean and adjusting to it will certainly work, and maybe it can be quicker that way. It's very scientific of course -- Germanic -- but overkill. The object is simply to get all the intakes equal. You can read fancy vacuum gauges, or look at little balls. Same result. When they are equal, you may wind up with the idle a bit high or low, in which case you just decrease or increase each screw the same amount to get the idle where you want it.
I'm sure you have the linkages set correctly, and I'm probably misinterpreting your words, but to be doubly certain you don't want to set them to just evenly close the butterflies alone. There are stop screw adjustments on each of the butterflies to do that. Disconnect the linkages and set the stop screws so that the butterflies are all just closed when they rest on the stops. Then adjust the linkages so that when you pop them on they don't move the butterflies off their stops. The bleed screws then simply allow you to account for very small differences in each butterfly/stack. If all the intake stacks and butterflies where accurate, precise devices, you wouldn't need the bleed screws.
One more thing. If you have one cylinder that
consistently fouls, like Josh's #2, double check the linkage/butterfly/air screw on that
one. It's often the probelm.
Hope this helps.
Date: Sun, 26 Mar 2000 23:49:0
The cam in the MFI pump is matched to the cams in the
engine. Changing your cams can cause rough running. But that can be okay for
increased performance. (I had a "T" pump with "Solex" cams,
switched to an "S" pump and found it runs much better).
2) Frequent backfiring through the stacks
-- primarily from cyls 2 & 5.
-- No idea (see Bob Spindel's previous
3) Lots of backfiring through the exhaust --
mostly when decelerating but not always.
Date: Mon, 27 Mar 2000 09:42:15 EST
PorschePoor@hotmail.com wrote :
> After spending the last 6 months rebuilding my 2.2S
> Question: If adjusting the air screws on the TB's doesn't change idle
> speed one whit, despite running them out past ten turns from stops, am I
> correct in assuming that the fuel at idle is too lean?
> If the problem lies in adjusting the pump, is there any base point to start
> from similar to the TB air mixture screws? (i.e. screw in until stop is
> reached & back out 5 half turns). <<
Not that I know of. When I got my last pump rebuilt,
it was not even close to a setting that would allow the engine to run, even though Hans
said it would run fine without adjustment.
If your pump's main setting (mid range mixture) is set
extremely rich or lean, the idle air screws will not do much of anything. Also the
pump's idle screw will not do much -- you need to set the "part load"
(remove allen bolt in front of pump and use a long thin screwdriver) before setting the
"Idle mixture" (this special tool stuck through the fan). You do have the
CHECK/MEASURE/ADJUST manual??? (I can copy if you
> This is all rather frustrating as the fuel system worked fine before I
> pulled the motor, and I didn't touch the pump other
than to remove and set aside.
That points to something other than the pump. You
must follow the manual and check each component before blaming the pump. As the
manual says :
"Remember, the injection system is not a separate
component, as, for example, the generator. It should be thought of as part of the
engine. No matter how well the injection system is adjusted, it cannot make up for
problems in the operating condition of the engine. Always begin injection work by
checking the engine's basic tune."
The checking sequence is:
1. Air cleaner cartridge (rubber gaskets in place? filter
2. Compression loss (what is your compression? Maybe the
cams are not timed right???)
3. Spark plugs (are they all firing correctly? some new
plugs are DOA)
4. Dwell Angle
5. Timing (are you 180 degrees off, or off a tooth on the
distributor? Check that at TDC your distributor rotor is pointing to the #1 notch on
the distributor case.)
6. Fuel pressure and flow: should be about 10PSI at the
pump, you can TEE in a cheap gauge for a quick reading.
7. Injection nozzles: when you rebuilt the engine you
should have had the injectors tested/ cleaned.
8. Injection timing: not hard to check and adjust close
enough suing a mirror, as per manual.
9. Correlation (lengths of throttle rods etc)
10. Exhaust emission test:
a) part load -- I could
write a book about ways of doing this...
b) idle -- never seemed to
make much difference on many engines.
NEVER DEVIATE FROM THIS SEQUENCE (or Hans will poke you
with a long cheesehead screwdriver).
Date: Mon, 27 Mar 2000 10:32:34 EST
throttle rods. I can't believe that 5mm plus or minus is allowable... get them all as exact as you can. Do not worry to much about the angles of the throttle cams... getting the rod lengths correct will take care of that problem. You might also need to time the pump to the camshaft...requiring some mirror work!
After all adjustment is done, you will need a
very small screwdriver of some length to adjust the idle mixture and lean/rich mixture
control on the pump. (All this is in the manual). It took me a couple tries to
digest the information and make sense of the procedure, but after setting it up, I've had
zero problems -- with the exception of adjusting the richness depending on seasonal
cold... once in the winter, returning the setting for summer if it gets cold enough in New
From: Bob Spindel <firstname.lastname@example.org>
Date: Mon, 27 Mar 2000 10:34:41 -0800
I also think you're setting's way too
lean, but not because of the way your air bleed screws act (or don't act), rather because
of all the backfiring. The bleed screws actually make pretty minor changes in idle
even when everything else is correct.
You can also manually open the throttle by moving the
linkage, thus letting in more air while keeping the gas the same, thereby leaning the
mixture. If the idle smooths out, or speeds up,
you're too rich. When you're close to perfect, the
idle will get worse when you do either of these.
I don't know if there's a rough rule as you suggest. I do know that the mid-range adjustment is by far the most critical, and if you have it right the idle adjustment can be way off and things will still be okay. I also know that the mid-range adjustment is very fine. Each click is 1/6 turn, and the right setting is within +/- 2 - 4 clicks or so. That's less than a full turn. And the screw itself is pretty dang long with a very fine thread, and you can probably turn it a zillion times from stop to stop.
Doing what I wrote above ought to get you close, then do
what I posted before, which is lean out the mid-range adjustment until you start to
backfire like a banshee -- sounds like you're already there -- and then richen it
as I described.
Hope this helps.
P.S. John Hunt suggested if you're in the Pacific NW
you should contact Chris, at Chris' German Auto in Bellevue, WA. I agree, he's
excellent. (Coincidentally, I'm in Bellevue too!)