Big E

Well, I'm nearing the end of my rope on the possible causes to the project car's inability to start. I have looked at every input to the DME, at the connector to the DME, and they all checkout fine and fall within the specs listed in the factory manuals. This includes the speed/reference mark using a scope. Just as I'm writing this, I can't remember if I checked the Hall sender, but I think so.

Assuming the Hall sender is good, everything going into the DME checks out. However, it is not sending a pulse to fire the spark. I don't have a breakout box (yet), so I can't look at the signal real-time, but I verified the wiring and the ignition final stage by generating a pulse on the appropriate pinout of the DME and saw the pulse at the coil. The only thing I really haven't looked at in detail is the injectors, but it seems like the spark pulse should be there anyway.

Any thoughts? I am now considering actually building a circuit (well, several) to drive the DME inputs, and see if I can get a signal out. I'm very hesitant to run out and plunk down for a new/rebuilt DME without really feeling confident this one's bad.

This is on a '88 944S.

Thanks

Tabor

What would really be cool is if you built a DME test harness. Good luck, at least you have the skills.

Big E

That's where I'm heading...

Bryan

You most likely have a bad DME brain. I had the same problem with my '88 plain-jane 944. Sometimes it started and ran great. Sometimes it started and then shut off like someone swiched off the key. Sometimes it would not start at all, the problem being no spark. Somtimes it would misfire violently while driving. I did the same thing you did - buzzed out the whole harness from the DME connection end, checked every input to the DME brain, and everything checked out fine. I then took my DME brain apart, wiggled things around, and the problem went away for a while. Well, it's back, the blasted thing. My car's been off the road while I did a head gasket, waterpump, etc. Finished the project Sunday afternoon, started the car, and all the old bad DME brain symptoms returned. You know the story about Elvis shooting holes in his Pantera? I'm about there with this car. So I finally ponied up the dough for a remanufactured DME brain. I'm getting mine through Foreign Intrigue for $428.80 plus $50 core. It's reached the point where the frustration ending and the peace of mind that the thing's not going to strand me somewhere is worth the couple hundred bucks.

I'm sure it's a couple 3 cent components somewhere on one of the boards, but like I said - heck with it, I want the car up and running NOW and will have my new brain by this weekend.

Starting to understand the appeal of the Japanese cars now...

Bryan

Andrew

Make sure your spark plug wires are in corectly. This was a problem with my car but it was a guy that was mad at me that changed them on me. i didn't understand why i would only have two cylinders run. Anyway, i went through the same stuff just to find that the wires were swaped. just check in case.

Joel

Does your car have an alarm? A friend of mine forgot to connect the little black box under the dash after an engine rebuild project. For the life of him he couldn't get the car started. Once he reconnected the box the car fired right up.

jim968

FWIW, my buddy / professional wrench has seen several of our cars with problems in the wiring harness near the brain; apparently the conductor in the wire becomes brittle with age & breaks. Sometimes a bear to find, because bending the harness to a different angle while troubleshooting can re-establish continuity thru the bad wire temporarily.

Jim, you gotta love the quality materials Porsche uses sometimes....

eworkley

Problems with the DME that are extreamly hard to troubleshoot can come from a cold solder joint or a solder connection that has loosened from the vibration. I was crusin one night about 50 miles from home and my 944 shut down. Had it towed home...started troubleshooting and several (many) hours later found the chip in the DME had worked its way out. It didn't have a retaining clip!


eworkley
87944s

Hans

Hope link works and is of help. http://persweb.direct.ca/aschwenk/De...nicSystems.htm
The site has a description of the Bosch D & L type Motronics systems.
Good luck and let us know