After trying to figure out why the rear knock sensor code was coming up on the S52 swap (after 6 months of no codes), I finally decided to check the wiring between the DME and the sensors. I should have done this earlier as I thought the DME wasn't seeing the rear sensor from the way it acted. The thing that threw me was the other DME I had plugged in from a 325is didn't show the CEL. I checked that DME with the Peake tool and there it was; Code 45, rear knock sensor. Since the CEL never came on with the 325is DME I never checked with the Peake tool.
Rear knock sensor signal wire: NO continuity between the sensor and the DME.
The sensor has 2 wires under the rubber boot, although it only looks like one wire. There is a ground wire and the signal wire.
Tested the front sensor and got continuity on both wires.
So I rigged up a bypass wire from the sensor signal wire directly to the wire in the DME (after testing the DME wire of course).
Fired her up and NO CEL.
Will take her out in the morning to confirm that was the fix, then I'll make it a part of the harness. Hopefully this will be the end of the story...
OK that appears to be what it was, a stupid broken wire in the harness, probably up near the area where the valve cover would hit it when R&R it to change the vanos unit. I found some abrasion marks on the tape wrapping the wire bundle.
Rear knock sensor signal wire: NO continuity between the sensor and the DME.
The sensor has 2 wires under the rubber boot, although it only looks like one wire. There is a ground wire and the signal wire.
Tested the front sensor and got continuity on both wires.
So I rigged up a bypass wire from the sensor signal wire directly to the wire in the DME (after testing the DME wire of course).
Fired her up and NO CEL.
Will take her out in the morning to confirm that was the fix, then I'll make it a part of the harness. Hopefully this will be the end of the story...
OK that appears to be what it was, a stupid broken wire in the harness, probably up near the area where the valve cover would hit it when R&R it to change the vanos unit. I found some abrasion marks on the tape wrapping the wire bundle.