Porsche Repair: no spark, air flow sensor, porsche 944

Question

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Followup To

Question -
i get no spark in my 86' porsche 944, started well before. Does the DME control the spark and fuel? Thanks

Answer -
Hi Alex,

The answer to your question is ABSOLUTELY.  The 944's Motronic system you have is very computer dependent.

Now, what to do about the no-spark situation.  Before you go out and buy another DME, I'd suggest checking all the other spark-related components first.  At a minimum, the coil is certainly suspect.  Both as to whether the connections are still in place and are clean; as well as whether the coil might just have failed.  Inside the distributor cap I'd do a very thorough check to make sure everything still appears new and brass looking items are clean.

After that the typical sequence would be to determine what inputs the DME gets, which it won't run with, and check them.  These are the sensors like the rpm sensor, air flow sensor and TDC sensor.

If you take one component at a time and you have a bit of patience and a bit of luck, the pretty Porsche will be alive very soon.

Dave

Thanks, didn't believe you can answer so quickly. Let me pull back a little: I'm 18 and my dad owns a body shop now for 14 years, however never really fixed porsches. THis is my first 1986 944, I'm currently restoring, coming to a completion. Before i bought the car, it wouldn't start every ounce in a while, and the battery was dead so i used a jumper many times. The cluster also jumped, and the milege didn't work. Than the cluster stopped working, but the car still ran. I changed the drivers door, and the "new" one came of an newer 944 i guess, because the wiring was different, i still tried connecting the wires, and tring out the power things, they didn't work, and now the car doesn't start at all. It won't give a spark, should i buy a DME relay? Or the DME computer? Or look for other relays that talk to the cluster? sorry about the long questions, you can call and ask for alex at 607-589-6853, if possible can i have your # or e-mail? Thanks

Answer
Hi Alex,

Thanks for the extra information...I still think you should check all the other ignition pieces first...but as for the new DME computer, it sure wouldn't hurt to have a "known" working computer.  If you swapped it in it would certainly help answer part of your quandary...either it would start the car or not.  Unless something else was still wrong.

But, for as long as you plan to own the car...it would be wonderful to have a good computer on hand just for analytical purposes, so if you can find one at a great price, I'd pick it up.

As for the DME relay, before you replace it, why don't you test it?  There should be an 85 and 86 terminal that if hooked to 12v and ground very briefly... the relay should click, meaning it's working.

Dave