CyCloNe!

Hey guys I have a 951 with an odd running issue.

1) Warmed up it is perfect in driving, boost, idle... afr is 14-15
2) 30min of idling warmed up it starts to surge and struggle to stay running, afr is reading in the 13-14 ranges when surging.
3) If i give it gas it bucks worse and afrs are in the 11's, seems fuel is coming
4) If i let off gas and it doesn't die it will continue to surge and afrs will be back in 13-14 range.
5) Only happens when warmed up for 30+ min and wont cut back on if turned off till cooled down.
6) Cannot drive it once it happens it would acceleration and I wonder if its ignition/spark based.

Things I've noticed:
1) I have unplugged dme temp sensor, car surges worse and dies
2) I have unplugged 02 sensor and tps car still does same issue
3) I have checked for vacuum leaks
4) FPR and Damper seems to be functioning no fuel in vac lines
5) Fuel pump is on and humming no surging sounds from it
6) Tapping/shaking DME while running changes nothing
7) Shaking Crank and Reference Sensor harness does nothing.

All sensors have been changed on this car, tune-up and all fuel system has been as well within passed 5yrs.

odonnell

Bad MAF? It sounds like the load it's reading isn't consistent and it's traveling to different parts of the maps that are close enough to keep the car running but wrong enough to cause it to run poorly.

CyCloNe!

Could be... I'll clean it first I don't have the tool that can pierce the wire to check it with my multi-meter. It's just kind of weird that I can even drive it on the highway for almost an hour and then when I idle it goes to poo and will shut off and not start.

951Dreams

A thought, DME temp sensor, unplugging makes it worse. But I wonder if it's getting way left field signals from it and totally hosing your mix. Normally I would think a once totally warmed up issue would be the DME temp sensor. Might look up the test over on Clark's and throw the MM on it. Just to see.

Or, you can be lazy just like me. Picked up a new blue one cheap, I'm just gonna replace it, it was cheaper than messing with it. Time/cost wise.

mytrplseven

If you followed my saga for the last year, trying to get my '86 turbo to run, I basically replaced the AFM (bad track), the entire ignition system, entire fuel system, injectors, rebuilt the turbo, new vacuum lines, AOS seals, TPS, DME temp sensor, etc. Bottom line, the DME was bad and as soon as I replaced it, it all fell into line and the engine ran great. Good luck with yours. If you can find a DME on loan to swap it out, it could clear up an issue that the symptoms are masking the real problem.

CyCloNe!

Ya I'm taking your advise before throwing money out or a bunch of hours of testing I contacted a lister to see if they have a DME I can test with first. I pulled mine out and looked it over it appears good but I don't have a magnifying glass to confirm the solder contacts and even if they are fine stil could bena faulty part on the board. Eventually I hope to get Josh's Rogue ECU but not in the cards yet.

mytrplseven

When I found mine, I went to the classifieds list and sent a WTB message with "loan for diagnostic, will buy if it works" post. You might consider that approach.

TurnerJ

On my 84 944 it would run perfect until warm and then run rough but not die. Unplugging o2 sensor didn't change anything. Replaced o2 sensor and back to running perfect.

AlphaOmegaPower

This sounds familiar. Had Intercooler to Turbo pipe slipped off

CyCloNe!

Update:
Still haven't found a solution but noticed something. The car shuts off at 30min every time and runs fine until then. What could run for 30min and get hot to caue a shut off? I changed dme relay and used a jumper fuel pump will run, seems to be ignition based. Ignition coil doesn't get hot, cap and rotor where a little rough so I sanded the contacts and put them back on. Changed the DME temp sensor, with no real change.

951Dreams

This is just throwing parts at it, but at this point, for my money, I'm banking on the DME.

It get's hot from power running through it, and a loose solder joint gives up the ghost... best I got for ya.

Also, I've heard that if the DME isn't getting a good ground, it can run hot.....

My cars history shows an incident of that about 15 years ago, or so say the shop notes.

CyCloNe!

I wonder if its the DME as well that why I posted about borrowing one to make sure. Shaking and or tapping makes no difference on it hot or cold I've notice. Only part I've changed was the DME temp sensor so far and it was looking rough anyway. I wouldn't be shocked if it was the crank sensors though either.

odonnell

Did you get anywhere with testing and cleaning the MAF? That thing works by heating a wire and letting air flow across it, at the most basic level. Wonder if when the engine bay and induction system is hot enough to heat soak the MAF and/or the incoming air, it's not giving real readings.

CyCloNe!

Yes I check it out all appears in working order with it.

Mongo

Have you checked for any loose grounds? Some of us 928 guys had warm running issues traced to loose ECU grounds (LH & EZK).