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Old 02-06-2016, 05:16 PM   #1
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Ground resistance, DME relay to ECU

I've been checking the wiring from the DME relay to the ECU trying to pin down the cause of a running issue. Car starts, runs a bit then dies, or runs and drives for awhile then dies, won't restart, then will, etc. I've already checked out the fuel delivery system with results in separate post.

So this afternoon I started going over the wiring from the DME and fuel injector relays and discovered what looks to be a faulty ground issue in the ground connectivity from the DME relay through the ECU to ground. After disconnecting the harnesses from the ECU, I triple checked the ground wiring from the relay to the ECU connection and the wiring for the main ECU connection to ground #9 and it all checked out with no resistance. However, when hooked up to the ECU the ground from the DME relay shows either 2 ohms of resistance or else no ground connection at all, sometimes one, sometimes the other. I identified the pin on the ECU that connects to the DME relay ground and checked connectivity from that pin directly and got the same results, either 2 ohms resistance or some of the time no ground at all. So it seems as if the circuitry inside the ECU itself is screwed up and resisting grounding the DME relay. Does that make sense? It seems like the fault is internal to the ECU. Could that be possible? I think I remember hearing that it is sometimes possible to repair a faulty ECU.
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Old 02-07-2016, 02:43 AM   #2
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If you can't borrow a good ecu to verify a problem with yours, I have used ECU Doctor in in FL with good results.
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Old 02-07-2016, 04:44 AM   #3
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You can reprogram a used DME to your car if you have the vin from the car it came out of. It doesn't happen often, but I do have people buy them from me because their DME went caput.
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Old 02-07-2016, 08:50 AM   #4
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Any codes?
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Old 02-07-2016, 12:24 PM   #5
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Thanks everyone for your responses. I'm going to go over everything again today, see if I get the same results. No CEL, but I think it's possible to have codes listed without triggering a CEL? I don't have any kind of code reader at the moment. No access to a good ECU to switch. If I can confirm the fault to the ECU I guess I'll have to see if it can be fixed or try Woody's suggestion. Woody, have you got any on hand? It's an '03 S.
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Old 02-07-2016, 12:38 PM   #6
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A bad sensor can cause the ECU to shut down the engine. It would be worth checking codes before you start replacing stuff.
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