Vorsicht

Another way to rule out the DME relay is to make a test lead as explained below. I actually carry one of these in my car in case my emergency relay somehow fails. Easy to make. This basically keeps the fuel pump on without the relay in its spot. Verbiage below is from shop manual. I would be very surprised if they have not already tested the relay.

"Pull DME relay (R53) off the Central Electrical
System and use a fuse-protected shopmade
jump lead to connect pin 30 to pin 87 b
(identifications 3 and 7 on Central Electrical
System). The fuel pump should now operate."

Vorsicht

Another thing I discovered during my rebuild adventures (Steve Weiner mentions it somewhere) is that as the flywheel sensor ages it does deteriorate and is subject to heat soak which causes the thing to die resulting in a "hot stall" condition.

Given your troubles and the fact that our cars are getting beyond their teen years I recommend you replace it. At the very least it is preventative maintenance. It's about a c-note IIRC.

Having said all that I am completely biased as pertains the flywheel sensor as it saved my bacon. Good luck, you will figure it out and we will be here waiting and watching!

pp000830

Not sure you have sorted out the issue yet but maybe it is an old school issue like loss of spark due to something in the coil powering circuit or fuel getting hot in a fuel line causing some sort of vapor lock? Does anyone have a procedure to identify either of these as the issue. In the old days if a car stalls and it will turn over after a squirt of starting fluid it would validate a fuel starvation issue.

earossi

No, the issue has not been sorted out yet. I am waiting for a sit down next week with my mechanic to review all that has been done and to discuss a path forward.

Vapor lock does not appear to be the issue. When a stall occurs, the engine will immediately start up perfectly normally. First crank of the starter and the engine fires right up. Or, if the car is moving, re-engaging the clutch will bump start the engine instantly. So, my issue is an instantaneous issue that immediately resets itself.

Early on, we did test and then change out both coils.

Thanks for your thoughts. I will report back the outcome of my discussion. I have a lot of questions that were brought forward on this thread that I had not thought through before.

Sandia man

My car had similar problems. Cured by replacing battery ground strap. Cheap and easy. The old one looked fine.

earossi

Sandia,

Thanks for sharing. I have a couple of questions. When you had your engine shutdown, were you always able to immediately restart it "perfectly"? I have experience about 30 to 40 stalls on my engine, and in every single case, the issue is very short-lived. So short lived, that if I get a stall, just popping the clutch will immediately result in an engine start. If the stall occurs as I roll to a stop, I re-engage the starter motor, and the motor instantly starts up without hesitation and idles perfectly. I would think that with an bad ground, such as was the case in your battery ground strap, that there might be a problem restarting until things cooled off a bit? Can you comment on that specific?

Thanks.

hkspwrsche

Please tell us you put s dme relay in it now?

axl911

Earossi. You really need the porsche tools to pull the engine codes to see if the engine is telling you something wrong.

Here is one possiblity that is WAY out there. We know the LTW flywheel causes stalling when coming to a stop possibly b/c the ISV can't open enogh to get air into the engine right? Here is another theory where this can happen. IF your fuel evap valve is not connected or working, the same can happen. When your engine is warmed up, the car will automatically when sensing idle condition, will open the valve to purge the fuel evap canister. At the same time, it will richen up the mixture. You checked this valve and its operation? It is that 1-way valve with a connector going to it at top of the connector tree on the left side of the engine.

Sandia man

Earosi, my stalls would occur with normal driving - a brief studder of the engine - not associated with any particular condition; usually followed by normal progress. Illogical I know but the ground cable replacement fixed it once and for ever.

nine9six

If your wrench has a Hammer, PST-2, or PIWIS diagnostics tester, he should be just fine. If not, not so much

earossi

Thanks so much for your posting. The car is not throwing any codes at all. But, you did introduce something that we may not have looked at.....an non-operating fuel eval valve. I will admit that I did not even know of its existence. I have an appointment with my mechanic tomorrow to go over all the effort he has put into the car. I"ll bring up this issue for discussion.

earossi

OK, it's been almost a month since I have been able to sit down with the shop owner who has my car. I took with me, all of the unanswered questions that have appeared in this thread.

So, here is the essence of my discussion with the technician:

1. Early on they did replace the DME relay and saw no difference in the stalling issue.

2. Tested the flywheel speed sensor and believe it to be in good operating condition. And, the circumstances of stalling phenomena don't appear to be related to an intermittent malfunctioning speed sensor.

3. Tested the potentiometer that is the Throttle Position Sensor, and found it to be functional and repeatable.

4. Early on two of the "new" replacement O2 sensors were replaced since they triggered a CEL. The O2 sensors could contribute to the excess CO readings, but it is felt that this is not the root cause of the stalling issue.

5. Electrical grounding. Early on, all the chassis ground points were inspected and cleaned.

6. Engine head temperature sensor was replaced with a new one. There was no change in the stalling.

The tech believes that the issue is fuel, rather than ignition related. Furthermore, they have determined that they can now instigate a stall as soon as the engine aux air pump shuts down (less than one minute after the start of a cold engine). Once the air pump has shut off, they can force a stall simply by blipping the throttle without a load on the engine, to about 3000 rpm. Though the engine will not stall every time the throttle is blipped, they can get the engine to stall. When a stall is underway, engine RPM will plummet from the speed achieved from blipping the throttle. On other tests, engine speed following throttle blipping that does NOT involve a stall is observed to drift down slowly from the blipped speed to idle.

AXL911 - I discussed your "way out there" thought that a malfunctioning Fuel Evap Valve could exacerbate a stall given that the car is fitted with a LWF. My tech was intrigued with that idea and will take a close look at the valve. Stay posted on that.

In discussing next steps forward, they are going to review the electrical wiring and vacuum lines to all the solenoid vacuum valves on the engine. I replaced the engine wiring harness on the engine, and there is a possibility that two or more of the connectors for the solenoid vacuum switches were inadvertently reversed. He noted that this is one area where the Porsche wiring harness is not "idiot proof". In most cases, electrical connectors on the harness are specific to the device they supply power to; however, the (6) solenoids are all supplied through connectors that are identical. So, it is possible that I may have reversed two or more of the connectors when I installed the harness. They will review the color coding of each connector to make certain they are installed correctly.

Lastly, another technician who has not worked on my car will be assigned to the car. The thought is that he brings a new set of eyes to the issue, without being pre-disposed to what the problems are. This "cold eyes" review of the car may find something overlooked by the first tech.

I'll keep the forum posted.

uniquenamehere

I missed the fact that your car has a LWF installed... mmmm

earossi

The car has had a LWF in it for the last 4 years. A little over 20k miles have been run with the LWF installed; and, in my experience the car is rock steady with the LWF. My stalling issue did not manifest itself until I did a complete rebuild on the motor at 107k miles. Prior to the rebuild, I can't tell you the last time I had the engine stall. Driving with a LWF is not very forgiving if you are lazy in the use of the clutch. But, if you drive the car properly, the LWF is a wonderful thing in that it allows the engine to speed up very nicely.

LWF's installed in 1995 993's are a different story, I'm told. But, my car is a 1998 model.

axl911

"AXL911 - I discussed your "way out there" thought that a malfunctioning Fuel Evap Valve could exacerbate a stall given that the car is fitted with a LWF. My tech was intrigued with that idea and will take a close look at the valve. Stay posted on that."

Testing the valve is simple. A 12v signal is applied and the valve opens allowing the car to suck in the air from the Fuel Evap canister. Maybe it got stuck open or stuck closed.

Pull it out, apply 12V, see if you can blow thru it.