I replaced the head gasket on a 1996 E320 (M104 engine). I reconnected the wiring harness and now I have no ignition spark and no fuel injector pulse. What are the authority sensors necessary to get the electrons flowing properly in the PCM?

I think the bad wiring harness issue was fixed prior to 1996. I want to look at the signals from the authority sensors going to the PCM. If the inputs are good, I want to look at the outputs to the coils and injectors. My impression is that www.startekinfo.com is a reasonable source for wiring diagrams to assist in this process. Any insights into this problem would be apppreciated.

I don't have a diagram in front of me, but what about the position sensors? Cam and crank? those provide timing feedback to the computer. Also the fuel pressure regulator maybe? Why did you replace your head gasket? I have a 96 SL320 and I am hoping I don't have to do that anytime soon. 135k. I have data on a 95 104, I will look at it tonight.

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Brian W. Heitman

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I replaced the head gasket because the old one leaked oil (typical for this engine at about 100K). I think that 1996 was the first ODBII year and the wiring scheme changed from 1995 when this engine was used in, for example, the 124 chassis series. I have the W124 CD and my wiring looks nothing like that illustrated in the CD. I agree that a position sensor or ECT sensor (or its wiring) is a likely culprit. I want to test the signals from these sensors by backprobing at the PCM connector to verify that good data is actually getting to the computer.

I agree about the wiring harness, I think in 96 due to OBD II the harness was changed out. I have not replaced mine and have not had any issues. I had an oil leak when I got the car, but it was just the front timing cover seal, the head cover gasket and the front main seal. I am at 135 and I am hoping my head gasket doesn't go because I would hate to have to replace that myself. I just freak out about all that cama nd timing stuff, I am afraid I won't get it right. Good luck!
Brian

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Brian W. Heitman

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