[ds968]

Yesterday after an uneventful half hour drive and three different stops for various errands, just about a minute after I left the last store, when I stopped at a traffic light, the engine suddenly stalled .  I started  it again ( in a panic because there were several cars behind me, and the first one did not seem to have any space to drive around me, nor could he back up without the other cars behind him backing up, causing traffic havoc...but I digress ..)  .  After starting it, the rpm needle was jumping all over the place,  racing, stumbling, etc.   I drove it for about 4 blocks ( and that was a chore, as it was hesitating to accelerate, and showing signs of near stall again , so I kept it in first gear and high rpm ) until I got to a nearby parking lot .   From quite a few previous similar experiences I knew this was the DME relay failing .  Lucky I always keep a spare DME in my glove compartment .  So I switched it, and sure enough, the car idled perfectly right away, and the drive home was without the slightest symptom of anything being wrong .    I always keep a spare DME in the garage also, so they’re always in stock . 

The only other time I’ve had the car stall out it was due to a vacuum hose disconnecting, but the stall out when coming to a stop has always been the DME .  I probably went through a dozen DMEs in the last 25 years or so .. 

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[ds968]

Well, crap !   I spoke too soon .   Started the car this morning , drove to a doctor’s appointment 5 minutes away, and then after about half an hour I drove for 25 minutes until I got to the work.  Combination of highway and streets with various stop lights .  Smooth as silk.  But then, I had a lunch appointment so when I went to the car to drive away , it started and then stalled within 1-2 seconds.  Started it again, and it did the same thing.  It rumbles very rough, shakes a bit , and then stalls immediately .  Tried a third time nd no luck .  So WTF now ?!   No clue what it could be,    The distributor is new, the spark plug wires are new , I can’t see any vacuum hoses popped out of their fittings ..   and no idea why the new DME worked perfectly for a day and a half , resolving the first stalling symptom , but now this !   I’m stumped .    Any ideas what to look for ? 

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[lbpesq]

Bad new DME?   I’d try another.

 

Bill

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[ds968]

Will do . 

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[Inkedupfatboy]

You could do a HAL9000 and put the original back in, just don't get out of the car - lol

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[oppositelock]

Try replacement DME relay first to eliminate coincidence. If still present, it's either spark or fuel, with spark being more common. Check the pick up sensor wires coming out the back of the distributor. If nothing obvious, it's back to old school troubleshooting.  Fire it up and point a temp gun at the exhaust manifold runners to see which are hot and which are cold. Troubleshoot the cold ones to find out. Good luck!

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[ds968]

Try replacement DME relay first to eliminate coincidence. If still present, it's either spark or fuel, with spark being more common. Check the pick up sensor wires coming out the back of the distributor. If nothing obvious, it's back to old school troubleshooting.  Fire it up and point a temp gun at the exhaust manifold runners to see which are hot and which are cold. Troubleshoot the cold ones to find out. Good luck!

thanks , will do. 

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[unknown4u]

The rpm needle was jumping all over the place



You will only get that if there is less voltage. But you say that you can crank the car at normal rpm? In that case the instrumentcluster will have not enough volts to work properly.



This is a symptom of a bad connection from either the minus or plus connections.



It results in a sweeping rpm needle.



Can you start the car and then try to move the the electrical harnas inside the car under the relayboard. Perhaps you have a loose connection overthere. Perhaps there is a problem. This because you do have the airbagissue as well.



So many dme failures are not common. I have never changed it the last 20 years I own the car.

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[ds968]

I can crank the car with no problem, and it fires up but now it stalls immediately. The needle jumped all over the place until I changed the DME.  After that it idled normally for a day and a half .  On this latest round though I can’t watch how it idles because it dies too quickly after firing up the engine . 

 

The wires / electrical harness under the relay board ?   What and where is that relay board ?  You mean the relays box in the engine bay ?  There are wires under it ?  

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[unknown4u]

Yes that board

And then inside the car there is a a complete spagetti because every wire from the car comes together.



But the dme does two things. It fires up the fuelpump and it provides the stabilizer for the necessary voltage.

Perhaps your stabilizer is the fault.

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[ds968]

I’ve heard of ICVs getting sticky with age , so maybe that explains why changing the DME worked for a while, it could have given it a new “jump start”  but then the valve might have just gotten worse by the following day . I’ll have the shop check that out also . 

I think they can be cleaned ( I may be wrong ) , but if not replacement is in order .. 

 

Thanks for all the guidance !   

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[ds968]

So today’s twist of events :  I asked my friend ( Bob , aka “ flash “ who is a 968 guru, and also the designer of the 968 Supercharger  ) who lives just about ten houses away from me , to load up his Durametric , and give me a ride to the car to see if he can troubleshoot what may be wrong,  and also physically check some things out with the engine .  He checked out the engine, vacuum  hoses connections, distributor cables to see if they’re all tight, etc.  Found nothing out of order visually.   So before we connected the Durametric I told him to see and hear what the car is doing when I start it ..  I got in the car, started it and …inexplicably it’s idling perfectly.  I revved it up several times to high RPM and let it drop back , and perfectky normal idling again .  

I turned it off, started it back again after a minute , and let it idle for a while .  No stumbling , no stalling, not shaking and sounding like a tractor, or as if it was firing on only 2 cylinders, so not a single symptom which manifested on Friday .   So I decided to drive back home , with him following , just in case .   Ran like a champ all the way home.   So we sat down over a beer, and I said ; What TF do I make of this ?  He thinks it’s possible the DME pins may not be making a clean contact all the time with the ports it goes into , and suggested I take the DME out, spray some CRC electrical cleaner in there, put the DME in and out in and out in and out a few times, then leave it out so things can dry and then put it back in .  And see what happens.  I’ll drive it around the block here so it’s close to home , the next day I’ll do the same thing, and so on for about three or four days to see how it acts .  

And now for the weird part : the air bag light with which I had problems for weeks, is not on more than the first second or two after starting the car .   Bob thinks there is also a possibility since the DME relay sends signals to the ECU, a dirty contact can cause the ECU to throw a fault code, even the airbag one .

I’ll clean everything today if I have time  ( he recommended I do that with all the relays , not just the DME ) and then see on the next first start of the morning what happens with that alert .  

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[unknown4u]

Bad connections.. can give you a headache. So it is was good that Bob was in town. ?

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[ds968]

The airbag light came back on today .   Ugh, back to troubleshooting that .   But the two starts today worked ok, so I’ll drive if a little bit and close by tomorrow. 

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[72911SMFI]

damn, I wish I had lived next to flash!

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[ds968]

damn, I wish I had lived next to flash!

The funny part is that he didn’t do anything at all this time, the car started and ran fine , all on its own.    When we were there I said ; thanks , but in reality it’s thanks for nothing ..  he laughed and said : you don’t know it’s “nothing” , standing next to it the car recognized me as the father of the SC I designed and installed in it ( he did the installation on my car , and then tuned / fine-tuned it while I was driving it ) and decided it better not f**k with me , and started out of respect ..or fear .  

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[ds968]

Just had another thought in this :   the problem occurred only on a day where I drove more than 30-45 minutes, but then started again with no problems after it sat overnight .   Is it possible that when the engine heats up some component ( maybe the relay box base ? ) expands and causes a loss of full contact , but then when cooled down completely it contracts back to “normal” connection ?  

 

( edit ) .. probably a dumb theory ; if that was the case , why would it do it only now , after 25 years of driving and 120,000 miles.. the engine has always gotten hot before. 

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[lbpesq]

Sounds like Flash laid his hands upon your 968 and the problem was cured!   I miss Flash, the 968 whisperer.

 

Bill

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[unknown4u]

Perhaps your connectors inside the relayboard are not strong enough. Especially the pins from the dme.....



You can open the board when it is out of the car. I have done that years ago. You can do nothing wrong. It is build for dummies.



Can can crimp al the connectors and the put it layer by layer together. The connectors underside are locked with a central mechanism.



A slim and briljant idea and gives you no trouble at all.

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[unknown4u]

A lose contact will produce heat by itselves.... in this case the connector will lose contact when getting hot. When hot no connection. When it cools down it crimps and will connect again.



A bad contact has a resistance. And resistance produce heat.....

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