964 Random Stalling

[SAM DACOSTA]

Greetings fellow Pelicans;

Help me by discussing this scenario. Last night I drove home on the wet streets of S. California (10 miles via 405 Fwy), the car ran with no issues until I reached 1/2 mile from home, then it cut-out while driving 4 times within the last 1/2 mile from home (but was able to re-start immediately).

There was no standing water that I drove through, did not have to use wipers home nor had any issues prior to these events. I have the under tray removed, could that has allowed excess water to get into something that would cause a stall? When I got home and garaged the car, I looked into the engine compartment and it was not excessively wet.

I decided to drive it again to work today, the roads were wet, no standing water, no wipers either and it drove without any issues. What's happening here guys?
Please share your thoughts and logical solutions.

Thanks...

[Don Plumley]

DME relay.
Wet coil wires.

[SAM DACOSTA]

Originally Posted by Don Plumley

DME relay.
Wet coil wires.

Thanks Don. I drove the car yesterday in the same weather conditions and the issue was not repeated. Over on 'Rennlist' it was suggested I spray the engine compartment with water (inside of a dark garage) and look for any arching from wires, etc. I did that last night but found nothing. Do I then just change out the DME relay, or is there a procedure to test if the relay is actually bad?

[bazar01]

Originally Posted by SAM DACOSTA

Thanks Don. Do I then just change out the DME relay, or is there a procedure to test if the relay is actually bad?

Only way to know if the DME relay is bad is if the issue comes up again, get ready with a triple jumper wire so you can jumper the DME relay socket. If it fixes the stalling issue, then the DME is the culprit.
It's hard to troubleshoot this kind of intermittent stalling issues. It is better just to wait for the car to bog down completely and unable to restart then troubleshoot it.
The question is, is it absence of spark or fuel issue?

Good luck!

[SAM DACOSTA]

Originally Posted by bazar01

Only way to know if the DME relay is bad is if the issue comes up again, get ready with a triple jumper wire so you can jumper the DME relay socket. If it fixes the stalling issue, then the DME is the culprit.
It's hard to troubleshoot this kind of intermittent stalling issues. It is better just to wait for the car to bog down completely and unable to restart then troubleshoot it.
The question is, is it absence of spark or fuel issue?

Good luck!

Thanks for the input. The scenario I described happened only one day (but 4 times within a 1/2 mile) and the car immediately re-started each time. If it's not the DME relay, then what?

Do you think that having the 'under tray' removed could have allowed too much water into the engine compartment, thus causing a short? Last night I did the 'arching test' recommended and found no arching issues inside the engine compartment or from the bottom while misting up.

Greatly appreciate the input.

[bazar01]

Originally Posted by SAM DACOSTA

If it's not the DME relay, then what? Could be a lot of things, like ignition switch supplying the switched power to various electrical components, loose connectors to AFM, loose or dirty ground points, etc.

Do you think that having the 'under tray' removed could have allowed too much water into the engine compartment, thus causing a short?
I have removed my undertray for 3 years now with no issues and I drive it in the rain. The only wires under there are the lower spark plug wires, O2 sensor and hall sensor on the flywheel.
Last night I did the 'arching test' recommended and found no arching issues inside the engine compartment or from the bottom while misting up.

Greatly appreciate the input.

My response in blue.

[SAM DACOSTA]

"bazar01" I'm going to look at the O2 sensor over the weekend, as I pulled it recently to install a 'cat bypass' and maybe it was not tightened enough . I thought I did but it has been mentioned here and on other sites, so I'm going to make sure of that, so I can eliminate that option.

Thanks.

[jasonmx5]

Everyone thinks I'm making this up, but I had a vacuum leak that caused intermittent stalling until I figured out what it was. Check the clamps and hoses around the ISV muffler just to be sure they aren't loose. Un-metered air was being sucked into the intake manifold causing hesitation, stalling, etc. My car has been perfect ever since I tightened up a few clamps.

[bazar01]

Originally Posted by jasonmx5

Everyone thinks I'm making this up, but I had a vacuum leak that caused intermittent stalling until I figured out what it was. Check the clamps and hoses around the ISV muffler just to be sure they aren't loose. Un-metered air was being sucked into the intake manifold causing hesitation, stalling, etc. My car has been perfect ever since I tightened up a few clamps.

I believe a huge vacuum leak can cause it to stall at idle or at a stop light. Try opening the oil filler cap while idling and it will cause the engine to stumble and die due to unmetered air leaning out the mix.

[91C2]

Happened to me and all the while I was worried after replacing the DME relay all is well. I also do not think there is a permanent fix to the DME realy going bad. I just wonder how long does it take before it goes bad again. What causes this to go bad?

[ischmitz]

Originally Posted by 91C2

Happened to me and all the while I was worried after replacing the DME relay all is well. I also do not think there is a permanent fix to the DME realy going bad. I just wonder how long does it take before it goes bad again. What causes this to go bad?

There was a batch of DME relays that has poor solder connections to begin with. I believe this was during the transition to lead-free solder. The absence of lead makes the solder joint more brittle and prone to cracking. It also requires different wave-soldering temperature profiles and thus some adaptation by the manufacturer. Combine the relatively heavy relay unit inside the DME relay box and the vibrations in the engine compartment and you have the perfect conditions for pre-mature failures. The relays are not glued to the PCB. They hold on just by the solder. Not only Porsche suffered from this. It is/was a well-known issues on VW and other Bosch Motronic platforms as well.

Ingo

[911jettat]

Originally Posted by SAM DACOSTA

...The scenario I described happened only one day (but 4 times within a 1/2 mile) and the car immediately re-started each time. If it's not the DME relay, then what?

Sam,
Are you still chasing this problem?

A couple years ago my O2 sensor was loose and would unscrew itself until it fell out while driving. It did it a couple times until I finally took the wheel off and got a wrench on it. Every time it fell out the power dropped by what felt like 100 hp, it didn't like to idle at all, and the car was insanely LOUD. Just throwing that out as a basis for more 02 info.

I've already mentioned to you that my stalling problem was related to a Wong chip upgrade that I didn't correctly seat into the DME under the seat. Keep in mind the stalling happened months after I installed the chip, so I never even thought to check it. I started tracking down the problem, and I thought it was my fuel pump... glad I didn't go through with replacing that!

Fuel pump dead? Man graciously finds his limit.

My car would stall, start back up, run strong for a while and then start back up. Eventually the frequency of the stalls increased...

[SAM DACOSTA]

"911jettat" I am still chasing the issue and have not been able to duplicate the random stalling. I checked the O2 sensor and it was tight. I misted inside the engine compartment (top and bottom) and checked for arching but found. I even started the car, had my wife hold the accelerator pedal to keep rpm's over 2000 and then sprayed underneath the engine compartment with a hose but no stalling episodes at all. I purchased a new DME relay and if the cars repeats the stalling, I'm going to change it out and see if that solves it at that specific time. But until then, the car is running good and the random stalling has never been repeated to date...

Kinda frustrated but what to do...

[91C2wrencher]

My '91 did this twice in its life. once was a sort of intermittant stumbling, my mechanic found sevral "loose" sparkplugs (ouch! I was sure I had set them in all perfect) problem solved. Once in was more of a random total electrical cut out, ended up replacing the "central electric"(fuse panel guts, pass. side under hood) never happened again. Although in hindsight it may have been just a loose harness plug under the panel, but changing the "central" cured it

[Pacific996]

Originally Posted by SAM DACOSTA

Thanks Don. I drove the car yesterday in the same weather conditions and the issue was not repeated. Over on 'Rennlist' it was suggested I spray the engine compartment with water (inside of a dark garage) and look for any arching from wires, etc. I did that last night but found nothing. Do I then just change out the DME relay, or is there a procedure to test if the relay is actually bad?

Wooo the suggestion of looking for arcing wires in the dark does not including spraying with water. Water is what gets into coil packs through cracks. All water would do anyway is spread the leaking voltage out so that it wouldn't be visible. The idea of looking for the blue fllashing arcing is to see if you notice the spark plug wires are worn out and just arc to the nearest ground they can get. Some times even light dirt traces can give a path to voltages going to your spark plugs from the coil.

[Newsboy]

Hopefully, your problem is gone for good. It may have been moisture related, but that also might have been a coincidence. The coils are hard to check with misting, since the coil covers prevent you from getting too close. If the problem re-occurs, and your coils have never been replaced,I'd start there, after trying a new DME relay.

[RSTarga]

I have this problem on occasion in the rain and when cold. I've replaced all the temp sensors etc. and it still does it. No fault codes show up. My mechanic thinks it might be an ignition switch problem but I am not sure. It definitely is temp related. It starts fine cold then after about a mile it just shuts off. Restarts right away on the starter, but won't refire by declutching . I have to turn ignition switch off and on again.

[code7rpd]

Has you airflow meter plug been modified per the TSB? I had a similar issue and found that although someone removed the wrap from the connector per the TSB, the boot was not wire tied and the wires were exposed. I would get random hesitation and cut off once in a while. After fixing the boot I have not had any problems since. Might be worth checking.

[SAM DACOSTA]

Originally Posted by code7rpd

Has you airflow meter plug been modified per the TSB? I had a similar issue and found that although someone removed the wrap from the connector per the TSB, the boot was not wire tied and the wires were exposed. I would get random hesitation and cut off once in a while. After fixing the boot I have not had any problems since. Might be worth checking.

Again, thanks for the input but I've never been able to duplicate the stalling issue and would still like to trouble shoot possibilities. You mentioned a TSB regarding 'airflow meter plug.' I'm not presently aware of any upgrade (I purchased the car last year July 09) but would be willing to look into it. Can you provide more details on where to find the TSB relating to the 'airflow meter plug' or just send me a link where to do the research please.

Thanks always...

[code7rpd]

Try this link for information. If you do a search on 'air flow meter' on Rennlist you will yield quite a bit of information.

http://www.pcarworkshop.com/images/b/ba/24_x_1990_620590geolab.pdf