1973 911e mfi keeps stalling need help!!!!

[pistolpete]

I have a 1973 911e mfi that starts and runs fine until I get it on a highway or secondary road and start to slow down to a light or off ramp. It will stall. It will start right up again. Could this be micro switch?? transducer or something else?? How would I try to troubleshoot these??

thanks chris

[Grady Clay]

Chris,
Welcome to the Forum.
You will find a lot of help here.

We need more information. Does it run out of power and die under load or simply not idle and die when off load?

The former is usually a fuel pick-up issue and the latter a mixture issue. More info please.

Some tests you can do is to go for an extended drive. Is there an issue after full throttle and up hill?

When it dies, does the idle simply go low and stop? Are there other symptoms? Does the exhaust ‘pop’ or other? What does it do if you give some throttle? Can you keep it running with throttle? Just prior, do you have full power available?

Please don’t adjust anything without consulting here. Random adjustment usually leads to more difficulty.

Best,
Grady

[drewbrown]

Chris, You have a speed sensor control problem. Its a little box over on left hand side by CDI.Just disconnect the wires at the switch (Push button rubber booted plunger)on the left intake side that is connected to linkage. It will idle a little bit higher when hot, but the stalling problem should go away. Or you could call Spencer Cox at Farnbacherloles and they troubleshoot it, charge you $3000.00 then try to sell you a 3.8 and put a big wing on the back!!!!!!!!!!!!!!!!!!! Just disconnect the wire, best of luck

[pistolpete]

does not die under load and I can keep it going if I keep the idle way up. Doesn't matter going up hill. It is when I come off load and slow up idle just goes down to nothing. Does not seem to have any power at the micro switch at anytime.

[Grady Clay]

Chris,

Disconnect the wire to the big electric solenoid on the MFI pump. Insulate the free wire as it gets 12 V power periodically.

Test drive and report.

Best,
Grady

[bkreigsr]

mine exhibits the same behavor when the timing and/or dwell is off by a degree or two. does it crank a bit longer at start?
Bill K

[BK911]

Excellent point Bill. I would check compression and ignition before I messed with the MFI. Search for "CMA" or "Check measure and adjust" for the MFI bible. This will walk you through some trouble shooting.

[kwikt 911]

Check the microswitch on the throttle stacks. Disconnect the wires and take it for a test drive. If it stays running but backfires when you let off the gas it could be the switch, rpm transducer or the shut off solenoid at the mfi pump.

[pistolpete]

tried both disconnecting the micro switch and disconnecting the fuel cut off and neither did anything. Any other ideas???

[kwikt 911]

Did you recheck timing and dwell? Did you pull the plugs? Maybe to lean? Rich? I'd pull the plugs before going any further.

[bkreigsr]

do you have a forced hot air supply to the thermostat on the pump?
Bill K

[tobluforu]

Ok, do you have the kit to adjust the pump, if so try adjusting the main enrichment 2 clicks rich, drive and if that does nothing, go 2 clicks lean from starting point. I just went through adjusting my pump, stacks, etc and my car did the same. I was trying to get it to run on the lean side which mfi cars hate. Would start fine, idle great, but when I would drive it and come to a stop sign, it would want to stall.
Like stated above, timing could be retarded to much?
Worth a shot.
PS How long have you had the car, more history on it and what you have done would help?

[pistolpete]

I since ran into another problem with the alternator so I will not be able to continue troubleshooting for about a week. But I will check the plugs and dwell,timing. I do have forced air to the pump (new hose). The next step will to check the pump when I get it up and running.

thanks for your help.

[Grady Clay]

Whoa Haus,

DO NOT ADJUST THE MFI PUMP!

Now is the time to go through CMA rigorously and completely. This may take several iterations of some parts. Please do not deviate, assumptions are the mother of all screw-ups. The point is to Check & Measure before you Adjust.

Keep in mind that CMA was written in ’68-’73, assuming new MFI. Our geriatric MFI needs additional care. Search Pelican under my name and CMA2.

Best,
Grady

[356RS]

100% agree with Grady and also Bill K about the thermostat hose.

[tobluforu]

Yea, because if you adjust the pump 2 clicks one way or another, your car will screw the pooch, give me a break! If this gets your car from not stalling, then I say do it which will at least help with the issue. Then one should follow the holy bible in regards to MFI cars in which is referred to as CMA or god only knows what can happen.

[Grady Clay]

Hasn’t the Forum had this discussion more than a few times?

Originally Posted by tobluforu

Yea, because if you adjust the pump 2 clicks one way or another, your car will screw the pooch, give me a break! If this gets your car from not stalling, then I say do it which will at least help with the issue. Then one should follow the holy bible in regards to MFI cars in which is referred to as CMA or god only knows what can happen.

Chris, pistolpete (10 posts as of this post.) has simply reported:

Originally Posted by pistolpete

I have a 1973 911e mfi that starts and runs fine until I get it on a highway or secondary road and start to slow down to a light or off ramp. It will stall. It will start right up again. Could this be micro switch?? transducer or something else?? How would I try to troubleshoot these??
thanks chris

Originally Posted by pistolpete

does not die under load and I can keep it going if I keep the idle way up. Doesn't matter going up hill. It is when I come off load and slow up idle just goes down to nothing. Does not seem to have any power at the micro switch at anytime.

Originally Posted by pistolpete

tried both disconnecting the micro switch and disconnecting the fuel cut off and neither did anything. Any other ideas???

Originally Posted by pistolpete

I since ran into another problem with the alternator so I will not be able to continue troubleshooting for about a week. But I will check the plugs and dwell,timing. I do have forced air to the pump (new hose). The next step will to check the pump when I get it up and running.
thanks for your help.

SO, what should we do to help a ‘new’ MFI owner. Obviously pistolpete has the skills to deal with MFI. Should we lead him down the path of more difficulty or help him solve the ‘issue’, whatever it is? He is giving good information and asking the ‘right’ questions.

Without knowing what Chris knows, it is irresponsible to light into Adjusting the MFI without Checking and Measuring the engine system first. All we can do is rely on Chris’ reasonably good description. We can help him ‘ask the right questions’.

I won’t claim to know what the issue(s) are with [pistolpete[/i]’s MFI. I do know that if you start ‘adjusting’ a reasonable running engine; you will typically soon get lost in the process and cause more issues than you cure.

CMA (and CMA2) leads you to find the easy problems (like closed points) before screwing with the MFI adjustments. CMA is not a “holy bible”, it is simple common sense dealing with a complex mechanical system and you don’t know all the details. The goal is to find out the issues.


I won’t discount that

… if you adjust the pump 2 clicks one way or another….

the running might improve. That might be because of some other issue. It is common knowledge that making an engine richer covers up other mechanical, running or adjustment issues.

Please don’t use the mixture adjustment as the first choice in solving a running issue.

One reason for using regular and complete CMA procedure is to maintain a ‘base line’ for the condition of an engine. Having a long-term base line, allows for far better diagnosis and resolution of even the simplest running issue. Complex issues without CMA are near to impossible to solve without starting from scratch. – a very expensive process but too commonly used.

Many (most?) of the CMA procedures are exactly the same as a prudent and complete ‘tune up’. No mystery there. Yes, there are a few procedures that are unique to MFI. That doesn’t negate the importance on all the ‘normal’ procedures.

Best,
Grady

[pistolpete]

Didn't realize I was starting a firestorm. I appreciate any input you have. I have always gotten great adivce from this forum. Living in the country and not having a knowlegeable porsche mechanic local (especially mfi). I rely on my limited skills and your help. The combination has served me well in the past. I will continue to troubleshoot as soon as I replace the alternator. Thanks again.

[Grady Clay]

Chris,

No ‘firestorn’, just reasonable discussion about the approach any prudent person would take to solve ANY MFI issue.

I respect Pelican tobluforu’s suggestions as they may be perfectly correct and easily solve the issue at hand.

The issue I bring up is for both solving your running issue and explain the best procedure for all MFI owners with wildly diverse problems.

If any of us have a ‘crystal ball’ ability to solve MFI issues, I suspect they can earn ‘big bucks’. I have never been able to do that. Careful and deliberate procedures have worked well for me for 40 years.

Best,
Grady

[quickr-2]

Hi Chris; I hope you did a compression,leakdown and VALVE ADJUSTMENT, to that engine,since I was over there. Everybody always blames the MFI for problems,when it turns out to be other issues[Ignition,valve adjustment,weak compression,worn guides ect.] Again,your pump may be lazy[worn],but you should tackle the baseline[basic engine troubleshooting/fundementals] before anything. While it may cost you some time doing the basics,you will always save money and SANITY in the longrun. Warmest Regards;Chris