MFI Pump adjustment and idle problems

['71 911E Coupe]

Hey everyone,

I was driving my E the other week and it would stall when coming off the clutch in 1st gear without any throttle. So I turned the part-load adjustment screw a little richer, I shaved the screwdriver down to fit in the hole, and it seems to be a little better. But I read that it has to go into the pump about 2 inches. When I made this adjustment it was only in about 1 inch, if that. So after I made this adjustment, I was doing a CO test on it, and it was reading about 3-4%. I have also read on here that at idle, the engines run good at 7%. Remember this is when the car was idling. While I was doign this test, after a little while, the idle started to drop and the engine stalled. Wierd? Out of the blue, I wasn't touching anything on the engine, and it was running good before that. So I would start it back up and it would stall at idle, but it would be fine with the throttle opened.

So I made marking on the part load adjustment tool at 1 inch, 1.5, and 2 inches. I put it in there today and pushed it a little and it went in to about 2 inches. I emrichened the mixture some, and then started then engine up. It was better but would still stall after you came off the throttle. So i turned it some more, started it up, and the problem seemed to disappear.

Do I have another problem here, or do you just think the pump is way off, BECAUSE when I got the car, the pump had a screw in it (see below) that was putting more fuel into the engine. The rod was the wrong length, and everything was a mess, but i fixed all of that and everything is set at it's stops. So could it be that the pump just needs to be enriched more now, that I got rid of that screw???? Or do I still have another problem?

Thanks!!!

['71 911E Coupe]

I read in a UP FIXING DER PORSCHE, that it could be the transducer. It says:

"Idle stall after blipping the accelerator or rapid deceleration is often caused by a defective fuel injection realy(tranducer) which fails to quickly re-establish the injection after overrun."


But when the problem did occur, it wouldn't even idle right after I started it up. But wouldn't this occur all of the time if it was the transducer???

And at idle, the screw does touch the micro-switch like it should, according to CMA.

Any thoughts or help is greatly appericated! Thanks!

[Zeke]

Originally Posted by '71 911E Coupe

And at idle, the screw does touch the micro-switch like it should, according to CMA.

Any thoughts or help is greatly appericated! Thanks!

Mine touched but didn't close the switch every time. check that. Beyond that, I don't know off hand.

[304065]

Which way did you turn it?

After a while at idle, the engine stalls. Why is this happening? The thermostat is heating up, leaning out the pump, causing the engine to stall.

But let's back up. Adjusting the idle mixture adjustment has nothing to do with keeping the engine from stalling. If you want to fix this problem, you need to systematically follow the Porsche test document called CHECK MEASURE ADJUST to make sure all the systems are at baseline BEFORE you turn any screws. You can start by ordering the correct paper thermostat hoses from Pelican, there are and inner and outer, to replace that blue rubber garden hose.

CMA can be found in the Ultimate MFI Resources thread, which you can find by searching. Read everything on that page and report back here and we can start systematically diagnosing the problem. Just turning the screws is more likely to result in you getting the system out of whack.

['71 911E Coupe]

Originally Posted by john_cramer

Which way did you turn it?

After a while at idle, the engine stalls. Why is this happening? The thermostat is heating up, leaning out the pump, causing the engine to stall.

But let's back up. Adjusting the idle mixture adjustment has nothing to do with keeping the engine from stalling. If you want to fix this problem, you need to systematically follow the Porsche test document called CHECK MEASURE ADJUST to make sure all the systems are at baseline BEFORE you turn any screws. You can start by ordering the correct paper thermostat hoses from Pelican, there are and inner and outer, to replace that blue rubber garden hose.

CMA can be found in the Ultimate MFI Resources thread, which you can find by searching. Read everything on that page and report back here and we can start systematically diagnosing the problem. Just turning the screws is more likely to result in you getting the system out of whack.

John,

So what you are saying is that if the pump is too lean, after the thermostat leans out the pump that could be a reason for it stalling. I didn't even think of that. But I did turn the screw counter-clockwise, to richen the mixture.

I do have a copy of CMA and did check mostly everything. Still have to check the timing, I have 4 timing lights and they are all bad! As a matter of a fact, I have CMA in front of me right now. So lets go down the list:

1. Air Cleaner Cartridge...I dont have the air cleaner on, so next one
2. Compression Loss.... I did a compression test and the numbers were all around 150.
3. Spark Plugs....New Plug, that I did remove a second time to clean, and a New set of Wires
4. Dwell Angle....I checked...it's right on!
5. Ignition Timing.... Got to do this one still
6.Fuel Pressure and Flow...I Got fuel..I know that for a fact
7. Injection Nozzles...Cleaned them, wish I could check them, and am going to ultra-sonic clean soon
8. Injection Timing...Got to check this one too
9. Correlation...I have everything correct...Pump rod 114mm exactly! and all of the throttle plates are on their stops.
10. Exhaust Emission Test...well I have the anlyzer and all...so this needs to be done again


I can get one of the proper hoses for the theromstat, I think the blue one looks bad too, but it does work, I have felt HOT air coming up it before.

Thanks!!!

['71 911E Coupe]

Originally Posted by milt

Mine touched but didn't close the switch every time. check that. Beyond that, I don't know off hand.

What did you do to fix this? Was the switch bad? Or do you think I should just lower the screw a little bit lower? It makes the "click" barely by enough. And it can be pressed down more. If you were to tap the throttle, sometimes it doesnt activate the microswitch. I lowered the screw according to CMA. Thanks!

[boxster03]

Grady will chime in here soon so hold tight for great advice.

Regarding the microswitch, car should be running at idle

you loosen the nut and turn the screw until you here the switch click then turn an additional 1/2 to 3/4 turn.

['71 911E Coupe]

Originally Posted by boxster03

Grady will chime in here soon so hold tight for great advice.

Regarding the microswitch, car should be running at idle

you loosen the nut and turn the screw until you here the switch click then turn an additional 1/2 to 3/4 turn.

Right and I did that, but sometimes it doesnt click, like if you were to barely open the throttle and let it return, it may not click. Do you think another turn would hurt?

[boxster03]

try doing it with the car off. for sure you can here it click then. back the screw all the way off the switch and then turn until you you get the click and do the 1/2 to 3/4 additional turn.

[Jeff Higgins]

Listen to John; you absolutely have to be systematic in your approach to MFI. Study CMA, learn it, and follow it to the letter. You cannot do part of it; you cannot pick it up somewhere in the middle. You cannot just start turning screws. You will get lost so fast you may never recover.

The screw that you are turning that is 2" inside the pump is the main rack adjustment. The idle adjustment is located on the flyweight assembly, and is affected by the spring loaded external hex head screw. The one you have to get at through the fan shroud, with a foot long tiny little socket head wrench. It is pushed in until its internal flat head screwdriver shaped end engages the low speed screw on the flyweight assembly. The adjustments run in the opposite direction of the main rack adjustments; left is lean, right is rich. It is far less sensitive than the main rack adjustment, generally taking about twice the number of clicks to have the same affect on mixture.

The adjustment of the microswitch screw on the rack is not all that important. Just make sure it trips the switch every time. If it's faulty, like stuck or something, it can turn into a real pain in the ass because your car will die all of the time. Just pull one of the leads and it will disable the shut off solenoid. All that solenoid does is cut fuel supply on decelleration; most folks will never even notice if it doesn't. Worst case is the car will pop and fart when you lift, but some of us think that's kind of cool anyway. I removed the whole system on my 3.0 MFI motor. To my great dissapointment, it doesn't pop and fart when I lift. I was hoping for the occasional big ass fireball. Oh well. The point is, it's one of those systems that you shouldn't get all wrapped around the axle over. If it's important to you to make it work, do so. If not, unplug it. It won't hurt anything.

[Zeke]

Originally Posted by '71 911E Coupe

What did you do to fix this? Was the switch bad? Or do you think I should just lower the screw a little bit lower? It makes the "click" barely by enough. And it can be pressed down more. If you were to tap the throttle, sometimes it doesnt activate the microswitch. I lowered the screw according to CMA. Thanks!

Heavier throttle return spring and some new ball joint linkage.

[304065]

Originally Posted by '71 911E Coupe

John,

So what you are saying is that if the pump is too lean, after the thermostat leans out the pump that could be a reason for it stalling. I didn't even think of that. But I did turn the screw counter-clockwise, to richen the mixture.

I do have a copy of CMA and did check mostly everything. Still have to check the timing, I have 4 timing lights and they are all bad! As a matter of a fact, I have CMA in front of me right now. So lets go down the list:

1. Air Cleaner Cartridge...I dont have the air cleaner on, so next one
2. Compression Loss.... I did a compression test and the numbers were all around 150.
3. Spark Plugs....New Plug, that I did remove a second time to clean, and a New set of Wires
4. Dwell Angle....I checked...it's right on!
5. Ignition Timing.... Got to do this one still
6.Fuel Pressure and Flow...I Got fuel..I know that for a fact
7. Injection Nozzles...Cleaned them, wish I could check them, and am going to ultra-sonic clean soon
8. Injection Timing...Got to check this one too
9. Correlation...I have everything correct...Pump rod 114mm exactly! and all of the throttle plates are on their stops.
10. Exhaust Emission Test...well I have the anlyzer and all...so this needs to be done again


I can get one of the proper hoses for the theromstat, I think the blue one looks bad too, but it does work, I have felt HOT air coming up it before.

Thanks!!!

If the air cleaner is clogged, the engine will be too rich. If missing, will be too lean.

Compression seems reasonable.

New plugs are a good starting point, I use NGK which are under $2 a piece so when they foul up you throw them in the garbage.

Dwell angle. Good! (Not super critical)

Ignition timing. Timing must be exact, if you have too much advance at idle you will never get the car to settle down to 950 rpm. If you have too much advance at 6000, you will blow holes in the piston tops. As distributors wear out. . . too much advance.

Fuel pressure and flow. Be careful with gasoline. Just having fuel is not enough, if you have too little flow, as when the filter or the tank screen clog, you will be chasing your tail trying to set the mixture, and mixture will be intermittent. Much has been written here by Early_S_Man (RIP) on how to test for flow.

Injector nozzles. If one or more are stuck open, this can cause all kinds of problems.

Injection timing. Follow the procedure in CMA with a mirror and a flashlight, it's easy enough to verify.

Correlation. What do your syncrometer measurements read? Did you see my thread on how to set correlation with the protractors, and then David's addendum with the factory bulletin eliminating the protractors? Critical reading. Correlation is the HARDEST step of CMA.

Smog. What kind of AFR gauge do you have? LM-1? Gunson?

As others have said, the reason you proceed in sequence is you have to eliminate progressive sources of problems BEFORE you touch the pump.

CMA also sets forth a procedure for setting the part-load adjustment (main rack) first and THEN the idle adjustment. If you do this backwards the car won't run right. Part load is best set with an LM-1 at a constant speed under load. Again, all laid out in CMA, except you don't use the huge box in the passenger footwell to measure CO!

[David E. Clark]

I'll chime in here for what it's worth. In addition to the excellent advice given by Jeff and John, in particular:

Originally Posted by Jeff Higgins

... [Y]ou absolutely have to be systematic in your approach to MFI. Study CMA, learn it, and follow it to the letter. You cannot do part of it; you cannot pick it up somewhere in the middle. You cannot just start turning screws. You will get lost so fast you may never recover.

Originally Posted by john_cramer

... CMA also sets forth a procedure for setting the part-load adjustment (main rack) first and THEN the idle adjustment. If you do this backwards the car won't run right. Part load is best set with an LM-1 at a constant speed under load. Again, all laid out in CMA, except you don't use the huge box in the passenger footwell to measure CO!

I recommend three checks:

(1) Easy: You should check the condition of the fuel filter. Although this is unlikely to be the entire answer, the MFI filter is prone to clogging and should be changed at regular intervals or else fuel starvation may occur. I realize that you checked and are getting fuel but filters get junk in them and this can lead to fuel starvation problems that are sometimes intermittant or that happen only at cetrain times. Don't forget to clean the screen in the bottom of the fuel tank!

(2) More difficult: Make certain that the thermostat is clean, getting hot air, and functioning properly. When hot, it should be completely shut off. This thread will help. The "blue rubber garden hose" that John pointed out has to go! Replace it with the proper hoses.

(3) Most difficult: You should check to make certain that all the linkage moves off idle simultaneously. I realize that you have checked correlation with the appropriate measurement but if all the linkages are not moving from their idle positions simultaneously you may experience the stalling problems you describe. While you are at it break out your synchrometer and check to make certain that the air flow at idle and just off idle is consistent for each cylinder. John's thread: The MFI Diaries: Correlation at LAST! should help along with the other sources listed in the MFI Message Board Index.

Good luck and please keep posting your solutions.

['71 911E Coupe]

Thanks for all of the replies and tips guys! I will run back through CMA and make sure to stay in order this time. Now I know some more pointers that I didnt before.

I did replace the fuel filter about 1 year ago. Guess I should check it. And the screen in the bottom of the tank is good, because I had the tank in two halves, then welded back together, because of rust.

I don't have protractors, So I have all of the plates closed off right now. I will double check all of the linkage, after all you guys are the experts. I dont use the throttle stop screws, I just have the air-correction (bleeder) screws turned 5 turns each or 2 1/2 half turns.

Let me go lower that screw for the shut-off selonid a little more....
And Ill go check the correlation too....
And Ill see how it runs and report back....

So you really dont need this shut-off switch?????

[David E. Clark]

Originally Posted by '71 911E Coupe

... I did replace the fuel filter about 1 year ago. Guess I should check it. And the screen in the bottom of the tank is good, because I had the tank in two halves, then welded back together, because of rust.

Are you sure you got all the rust out and the tank is now properly repaired and sealed?

Originally Posted by '71 911E Coupe

... I don't have protractors...

Where are you located?

Originally Posted by '71 911E Coupe

... So you really dont need this shut-off switch?????...

I have to disagree with Jeff on this one. Not only will you get backfiring, popping and "farting" from an improperly adjusted microswitch but if you disconnect the solenoid you will - as Jeff points out - continue to get excess fuel flow when you take your foot off the accelerator. Most MFI cars run rich (especially now that they are getting up in years) and the last thing they need is another potential source of plug fouling and/or excess fuel to potentially dilute the oil by running down the cylinder walls. Just my 2¢

[Jeff Higgins]

Anthony, just a couple of more points to consider.

The trottle stop screws are there for a reason, just not the one most folks would suspect. They are not used to adjust idle speed; the air screws do that. All throttle plates need to be fully closed and on their stops at idle. Do they make contact with the stop screws? It's important they do.

When rebuilding the throttle bodies, we hold them up to a light and make sure we cant't see any light past those closed throttle plates. Then we screw those stop screws in until they just kiss the throttle arms. The idea is to keep the closing spring pressure on the arm via the stop screw, rather than on the bores via the throttle plates. Those plates are one hell of a lot harder than those bores. If left to rest on the bores under spring pressure, they will soon wear grooves in and destroy those bores. Use the stop screws to prevent this. You can actually do this with the throttles on the cars, if you're careful. Just unhook all of the rods and let each plate close individually. Hopefully they are not so carboned up as to not want to do that. Then screw the stops in until they just take the load of the return springs. Some of those screws are a real pain to get to, and they are proably frozen in place, but it's important you do this.

You don't really need the protrators, either. With all of the throttles on their stops and the pump to rack rod length spot on, adjust the two rack to throttle body rods until they snap on without moving anything. That's the poor man's correlation. There was actually a Porsche bulletin released in the early '70's allowing for this method in the absence of the protractors.

And really, no, you do not need the shutoff switch. If it's giving you trouble, just disconnect it until you can fix it or find a new one. If you never fix it or find a new one, you're still just fine.

['71 911E Coupe]

Originally Posted by David E. Clark

Are you sure you got all the rust out and the tank is now properly repaired and sealed?



Where are you located?



I have to disagree with Jeff on this one. Not only will you get backfiring, popping and "farting" from an improperly adjusted microswitch but if you disconnect the solenoid you will - as Jeff points out - continue to get excess fuel flow when you take your foot off the accelerator. Most MFI cars run rich (especially now that they are getting up in years) and the last thing they need is another potential source of plug fouling and/or excess fuel to potentially dilute the oil by running down the cylinder walls. Just my 2¢

Yes the tanks was sandblasted and welded and I cleaned the screen til i could blow/suck through it.

I am in Southeaster Pennsylvania.

I lowered the screw a little bit and it hits the switch everytime now. I am going to make sure the switch is working though.

I ran the car and had no backfiring or stalling. I had "HISSING" through the stacks intermitingly at idle and at 1000-1400 RPM No backfiring through the stacks though.

Thanks

['71 911E Coupe]

Originally Posted by Jeff Higgins

Anthony, just a couple of more points to consider.

The trottle stop screws are there for a reason, just not the one most folks would suspect. They are not used to adjust idle speed; the air screws do that. All throttle plates need to be fully closed and on their stops at idle. Do they make contact with the stop screws? It's important they do.

When rebuilding the throttle bodies, we hold them up to a light and make sure we cant't see any light past those closed throttle plates. Then we screw those stop screws in until they just kiss the throttle arms. The idea is to keep the closing spring pressure on the arm via the stop screw, rather than on the bores via the throttle plates. Those plates are one hell of a lot harder than those bores. If left to rest on the bores under spring pressure, they will soon wear grooves in and destroy those bores. Use the stop screws to prevent this. You can actually do this with the throttles on the cars, if you're careful. Just unhook all of the rods and let each plate close individually. Hopefully they are not so carboned up as to not want to do that. Then screw the stops in until they just take the load of the return springs. Some of those screws are a real pain to get to, and they are proably frozen in place, but it's important you do this.

You don't really need the protrators, either. With all of the throttles on their stops and the pump to rack rod length spot on, adjust the two rack to throttle body rods until they snap on without moving anything. That's the poor man's correlation. There was actually a Porsche bulletin released in the early '70's allowing for this method in the absence of the protractors.

And really, no, you do not need the shutoff switch. If it's giving you trouble, just disconnect it until you can fix it or find a new one. If you never fix it or find a new one, you're still just fine.

Jeff,

Thanks, that is a lot of good help! I will do what you said with the screws, to take the spring tension off. I already had all of the stacks, and throttle bodies off of the engine in November, and cleaned everything up. So everything is cleaned and lubed up. I still spray so type of oil down the stacks to lubruciate the throttle bodies every so often. The seem to get stuck in place while the car sits for a few days and is cold out. I'm sure they need to be rebuilt, but that can wait until I take the engine out to freshen it up in years to come. I say this because, when I had them off, I did exactly what you said and held them up to the light and they were completely closed. I did a water leak test too! I was very susprised at the results.

And that is the document that I went by to set the correlation on the engine, the one from April 1972. I can't seem to post the picture though...but it says you no longer need protractors to set this, even though I bet protractors would be the way to go.

Thanks guys!

['71 911E Coupe]

Could this HISSING sound through the stacks at idle and up to 1400 PRM be caused by the timing? I don't have any pre-load on any cylinder, because when I pop the linkage off and put it back on, the thottle plate does not move, AT ALL (I MAY DARN SURE OF THIS). So correlation is out, correct? Could it be the fuel injectors leaking fuel, and not the right air/fuel ratio?

Isn't this sound from too much air? Please correct me if I am wrong. Anyone experience this before.

Thanks!

[David E. Clark]

Originally Posted by '71 911E Coupe

... even though I bet protractors would be the way to go...

I'm not sure. I finally found a pair of protractors (the larger one with pointer and one of the two identical smaller ones with one pointer) and was able to set correlation one side at a time. It was a pain in the a$$ and I'm not certain it is any better than getting the measurement perfect and making sure all the linkages move in unison off idle. Of course that was my first time and I was going by what I read in CMA, the factory workshop manual and the advice given here. I'm sure it would have been better if I had someone who knew what he was doing showing me the way.

Originally Posted by '71 911E Coupe

Could this HISSING sound through the stacks at idle and up to 1400 PRM be caused by the timing? I don't have any pre-load on any cylinder, because when I pop the linkage off and put it back on, the thottle plate does not move, AT ALL (I MAY DARN SURE OF THIS). So correlation is out, correct? Could it be the fuel injectors leaking fuel, and not the right air/fuel ratio?

Isn't this sound from too much air? Please correct me if I am wrong. Anyone experience this before.

Thanks!

I agree that hissing must be air - no fluid or mechanical piece would cause a hissing sound in my opinion. It's either air sucking or expelling. I would clean the air passages with a pipe cleaner and a product like B-12 chemtool as suggested in MFI Check Measure Adjust # 4532.21, page 23 and then synchronize the stacks again with the synchrometer. When you are adjusting the air passages, make sure that none are substantially more open or closed that the others and that none are open more than 8 turns.

Any chance that any of the seating gaskets from the throttle bodies or stacks are cracked or broken and letting air suck in through a small opening? That would cause a hissing-like sound - not to mention rough idle and running!