It sounds like you have determined that spark is present, but not fuel. Is it possible that an injector coil is (heat related) bad? One bad coil would bring down the rest. It sounds like you have checked/replaced about everything else. If you can verify spark and injector pulses with a noid light during a no-start period - and you have fuel pressure wouldn't that pretty much leave injectors? I commend you on your determination.

Just as a long shot you could pull the distributor cap off and see if there is any carbon from arcing and how rusted up the weights are.

I know this is a long shot and there are 18 reasons why this wouldn't be the cause but I have always wondered why those weights sticking isn't a problem. :)

Bill in OKC,
I have replaced the ignition coil, but I was not aware of an injector coil.
rick-l,
The distributor cap has been checked and is clean - almost new.

Thanks guys.

Each injector has a coil that energizes when it fires.

If all of the electrics have checked out, I would be looking at fuel. Yes, you have replaced the fuel filter and pump. But what about the fuel lines? I keep thinking that they are either getting blocked or collapsing upon themselves. You need to find out whether or not you are getting fuel when you stall.

To all the folks with a ton of experience. Is there any way that Scott can temporarily hook up a fuel pressure gauge in his cabin? That way he will see immediately what is happening on shutdown with regards to fuel. A hot Relay tells me that something is backing up in the fuel delivery process, in turn heating up the electrics.

I hope this may help.

And by the way, you have invested this much time already. Don't give up. You are almost home. :)

I was wondering if the weights that move the rotor as the spark advances were moving.

Does it have to be under load to stall it out or will any RPM excursion past 3000 stall it?

You don't suppose when you increase the frequency of the pulses to the injectors under load (heating them) one of them shorts out do you?

EDIT: I got mine from here

http://forums.pelicanparts.com/porsche-911-technical-forum/327832-alternative-fuel-injectors-13.html

You stated in post #34 you had 50-70 psi fuel pressure.This is too much. I had a 3.2 that had similar issues a long time back. I drove it with a fuel pressure gauge on it and when it stalled and quit running it had like 65-70 psi. The fuel pressure regulator was bad. I don't have my spec book with me at home, but I remember specs. being 40 psi or so.

If the fuel pressure goes high, the fuel mixture becomes very rich and floods the engine with fuel.

The regulator is a pain to get to. It is on the 1,2,3, left side of the engine behind #3 cylinder.

I second or third the bad injector coil. Let me know and I can send some injectors. You can try them out and if they solve the problem buy them, return them and get others or what ever but at least you can use them to test without buying more parts. By the way all the parts you have replaced pretty much needed replaced anyhow so don't feel too bad about that. It is just you didn't get to space it out. After you fix this you can start on all the rubber pieces. Sorry didn't need to (Hey what happend to the smilely poking a stick its gone.)

Oh man, you're still fighting this? :(

Some thoughts:

1. Gap between speed and reference sensors checked? Too big and at higher RPM will lose signal.
2. I think you need another known good DME. Maybe the DME is overheating and resetting.
3. Have you tried another airflow meter? If resistance is off, motor goes full lean IIRC.
4. Intermittent power loss from ignition switch?

CCM911,
We checked the fuel lines and they're in almost new condition. I like the idea of being able to check/monitor the fuel pressure while driving. I'd love to know how to do it.

rsscotty,
I'll check the fuel pressure regulator.

dfink and others,
I'll check the injector coils.

Tippy,
The gap for the sensors has been checked, .08mm I believe (off the top of my head), but we checked them to ensure they were correct.
As for the DME, I tried two known good DME's before I sent my out to Steve Wong to have him check and repair it.
I also tried a brand new Airflow Meter and Ignition switch.
Fortunately, my mechanic has a stock-pile of new parts. He's more frustrated than anyone here, as he's been working on these cars for 30 years, and this is driving him crazy. In central NJ, my mechanic the the guy all 911 owners go to, thus he's been losing his mind on this one.

Keep them coming and I'll get back to you.
Thanks to everyone.

>>I like the idea of being able to check/monitor the fuel pressure while driving. I'd love to know how to do it.

Summit, Jegs etc sell autolite gauges and they have fuel pressure isolators to allow you to run FP gauges inside the cabin... they use a diaphram thing and use antifreeze up to the gauge.

Chuck.H
'89 TurboLookTarga, 336k miles

The injector heating up seems to fit all the symptoms.

Could you run the car and get it to stall and then feel the six injectors and if one is hot pull the plug on that one and see if it starts?

another possible step would be when it won't start pull the connectors one at a time till it starts. This may disturb the bad injector to where it works for a while however.

You said you would check the injector coils. I don't think you can do it statically i.e. there is not a go/no go test at normal temperature.

>>I like the idea of being able to check/monitor the fuel pressure while driving. I'd love to know how to do it.

Summit, Jegs etc sell autolite gauges and they have fuel pressure isolators to allow you to run FP gauges inside the cabin... they use a diaphram thing and use antifreeze up to the gauge.

Chuck.H
'89 TurboLookTarga, 336k miles

Rick-I,
I can definitely get the car to stall out (unfortunately it happens all the time...). But you're saying once it stalls, feel each injector for heat, and if one if found to be very hot, pull the plug on that one and attempt to restart the car.

Two questions:
1) Does this mean that one bad/hot injector could cause the entire call to stall?
2) Would the car be able to restart with only 5 injectors plugged in?

Thanks.

Rick-I,
I can definitely get the car to stall out (unfortunately it happens all the time...). But you're saying once it stalls, feel each injector for heat, and if one if found to be very hot, pull the plug on that one and attempt to restart the car.

Two questions:
1) Does this mean that one bad/hot injector could cause the entire call to stall?
2) Would the car be able to restart with only 5 injectors plugged in?

Thanks.

Pull injector wires one at time and see if the engine stalls. You only have to try 6 times

This is an extreme idea but I think the only route you have left IMO:

Put the car on a dyno that can load the engine, hook up an oscilloscope to all of the sensor outputs with a breakout box, and take it up to 3000 RPM where it dies.

I would think it will point to what is going awry very quickly.

If all the waveforms are normal (of course they will fall off once the computer cuts out), the only thing left I can think of is take out the drivers seat, remove the cover off the DME, and rerun on the dyno that can load the engine.

See if any component is overheating.

With no onboard diagnostics, the oscilloscope is just about the only thing you can test the DME with.

Scott,

I just bought a 1986 with 85K that sat a few years. No one could get it started for months and replace many parts, reputable Porsche mechanic (before I arrive) even opened up the DME. Long story short: injector #5 was shorted out, meaning solenoid of the injector would not click when you apply power (12V) to it.

Yours may be heating up and shorting out. I believe that one shorted-out injector will cause DME to stop sending injection pulse as a protection.

normal ohm reading on injectors are 2-3 ohms, low impedance. All five good injectors were 2.3 ohms. The bad one (no click) was 3.3 ohms.

Do as Rick-I suggest, unplug the electrical of hottest injector and restart the car. It will run rougher on 5 cylinders, but will run. Good luck. Don't give up. Not much else to do.