3.2 Engine Stalling - Stumped
 

Over the past few months, my car stalls out under hard acceleration, always around 3000 - 3500 RPMs. When this happens, I install a spare DME relay, and the car starts up. Each time, the DME relay is hot to the touch. However, the DME relay is not bad at that point, as I've been able to use to again, after the car stalls. One more note, when the car stalls, the tach does not immediately drop to zero, the RPM's slowly go down with the speed of the car. I brought the car to my mechanic and here's what we've done:

- Checked and cleaned all grounds
- Check and cleaned the battery cables
- Replaced the TDC, CHT and RPM reference sensors
- Inspected the DME, and replaced it with a known spare DME
- Replaced the fuel pump relay
- Replaced the original fuel pump

After doing all of this, I still have the same problem and it's consistent. As an FYI, if I drive slow (under 3000 RPMs) or even go above 3000 RPMs gradually, I don't stall out. We are now looking into the anti-theft system to see if a short exists. This weekend we're going to by-pass this system to see if it has any affect on the problem. Today, we by-passed the anti-theft system, but got the same results (car stalls out). Today was the first time it wouldn't restart after installing a spare DME relay, we had to install another DME unit itself, but that too stalled out in the same fashion shortly thereafter.

Our next thoughts are the DME wiring harness (aka ECU wiring harness, engine harness). Does anyone have any thoughts on this. I've been reading thru forum posts on all these areas and have tried just about all of the advice found.

Thanks.

have you checked the voltage output of the alternator?

sounds electrical not mechanical to me...dont know - many years ago there was a company offering "break out boxes" for the 3.2 - my tech has one and can diagnose these things in short order..i suggest finding someone that has the right tools and spending a couple bucks to get it solved or at least on the right track..throwing money in parts at it is OK but frustrating and expensive....

last night my tech tweaked my car in a couple minutes and WOOWWW!!!! what a difference...worth every penny to me

You seem to have covered most of the major items. Does it just shutdown, or is their a missfire of some kind first?
Does this only occur when the full throttle switch is engaged?

Could be your air flow metre

Ed M.,

I was thinking of the alternator just before, we'll check the voltage tomorrow. What should the output level be?

Ed S.,

The engine just dies, no warning, no bucking, sputtering, or back-fire. It just quietly shuts off and the
car (and RPMs) coast to a stop.

ALXinNZ,

I have been reading up on the AFM, but don't have much knowledge on it yet.

Thanks all.

Have you looked into your fuel pickup in the tank? When was your filter changed last?

like some weird "ED"fest????


:p

do you have a Bentley manual?
there is an online version at cannell .uk something IIRC - search for it..the check is very well described in that...it is available for download too

Same happened to me. It was the fuel pump. Intermittant and hard to duplicate. The tech was convinced it was the relay. Try swapping a fuel pump out.

Here is a link for the AFM.
Air Flow Meter (AFM) - from "The 944 Motronic DME" by FR Wilk* ©2001 www.the944.com

Glenn,

I did replace the fuel pump (see above).

Ed H.

I replaced the fuel filter about 2k miles ago.

Ed S.

Thanks for the links, they are helpful, especially the link on the AFM. By the way, I do have the Bentley Manual - its great.

I'm going to test the AFM and alternator today, more to come.

Thanks all.

I feel for ya.

I wonder if a spike from the voltage regulator at higher RPM's causes the computer to shut down?

Ignition switch overheats?

Just some thoughts as you've done a lot of replacements to no avail.

I have almost the same problem with my '86 911. Same description of the stall, allthough it takes about 45 seconds before the engine will restart with the key. I've replaced the ignition coil, head-temp sensor, battery, crank sensor, DME and computer - all to no avail. I need help too! Eric

When this happened to my '89, it was the cracked solder joints in the DME - car would run great for a while, then occasionally it would stall. give it a few minutes and it would restart once the DME cooled.

It's not as scary as you think, if you're at all handy you can take the DME apart and inspect it. I re-soldered mine and it's been fine for the last 100k miles or so.

Be aware of any 'static' as it's getting towards winter time and the air is dry. Keep touching metal objects before opening the DME to avoid any static discharges thru the components and you'll be fine.

Look especially around the components that 'stand-up' from the board, like the coil power transistors in my case, since they put a lot of strain on the solder.

Hope this helps,
Chuck.H
'89 TurboLookTarga, 327k miles

My 3.2 did something similar to this and it turned out to be the fuel pressure regulator and dampener.
The regulator was allowing too much pressure to build up and the engine would shut off.

+1. I had the exact symptoms and it turned out to be cracked solder joints on the DME. Took all of 10 minutes to solder them up and 5 years later, I've never had this problem again.

Greetings again,

I figured it was time to give an update to my never-ending stall problem saga. Since the last time I posted in November, we've done a few things, but the same stalling problem persists. To date, we'd done the following:
- Checked and cleaned all grounds
- Check and cleaned the battery cables
- Replaced the TDC, CHT and RPM reference sensors
- Inspected the DME, and replaced it with a known spare good DME (just as a test)
- Replaced the DME relay (a number of times)
- Replaced the fuel pump relay
- Replaced the wiring harness - found a number of shorts/opens as well as vacuum leaks
- Replaced the fuel injection harness
- Inspected the AFM and replaced it with a new unit (just as a test)
- Inspected the wiring from the DME to the fuel pump - no problems found
- Inspected the anti-theft system - no problems found

We've done a lot of "preventive maintenance...", fortunately my mechanic has many new and known good used parts on the shelf to try things out. This weekend, we're going to replace the Ignition Switch, as this appears to be a known source for stalls. Needless to say, this stalling issue has become a nightmare. My mechanic (who's working on 911's for over 30 years) has never seen anything like this. I'm also picking up a new battery today, as my Interstate MTP-93 battery of 11 years finally died (can't complain about that). We have checked pretty much the entire car. When the car stalls, we open the DME relay and the portion that controls the fuel system is off, thus indicating the car isn't getting fuel (or it's run out of gas). Very very frustrating....

More to come after this weekend.

- Replaced the original fuel pump

you might want to check every one of the ground wires that bolt to the intake above #1 cylinder. they can break inside their insulation, and it's not obvious.

I can't tell but did you ever check the DME itself for broken solder joints as someone suggested earlier? This was an in issue on my '87 cab. The stalls were totally out of the blue and not nearly as specific a condition as yours, but it did seem to happen after it was warmed up, never cold, IIRC (it was YEARS ago). I took the DME apart and followed an excellent thread somewhere here on Pelican about what to look for. My eyes are not that good so it took full, bright sunlight and a magnifying glass to find them. Little scary resoldering them but it worked perfectly after that. Local Porsche Dealer wanted to charge me $1,600 for a new one.

This is a common theme over and over again; Carreras having issues no one can figure out.

I threw in the towel myself after spending hundreds of hours and dollars on mine not fixing the issue.

Good luck, been there done that.

It's easy to jumper the fuel pump to make it run without the DME, just run an alligator clip to the fuse that controls the fuel pump - can't remember which one, but they are labeled.

Since you have what seems to be a repeatable condition, it should be easy to track down - it sounds like a problem in either the power or ground of the relay control lines. IIRC, the power is fed to the relay by the ignition switch, and the DME grounds it to turn the pump on.

Just so I understand, when it stalls, it 'will not' restart with the same DME relay, but installing another (cooler) one will get it to restart? Then the relay is not happy, maybe too much current is going thru it, so check the above mentioned circuits.

@Tippy - I know you are frustrated by Motronic, but for me the system has been great, and has been easy to diagnose the occasional problems thru the years. My car starts right up cold or hot, runs smooth and strong, and the engine has never been rebuilt.

Chuck.H
'89 TurboLookTarga, 332k miles