e30 fuel economy gauge inop

[M1kEC]

Recently dropped a m42 into m40 car loving it atm but just noticed the fuel economy gauge is stuck over 50+mpg when running drops back down when ignition is of anyone able to point me in right direction

[DesktopDave]

Not sure about the M42, but I had the same problem with an M20B25 swap in an older E30. There was a separate signal wire off the DME that had to be spliced in. The DME has to send an injector signal to the cluster so the efficiency gauge works.

ETM says a white wire comes off pin 17 of the DME, goes to pin 8 of the round C101 chassis connector, then connects to a yellow/white wire that goes to pin 11 of connector C1 (the blue one) at the gauge cluster. You could probably splice it straight across the firwall, but I'd do it via the C101.

If that's not it, did you swap cluster coding chips? Could be that the M40 chip displays the M42 signal off the gauge. I'm not sure how different the cluster coding chips are.

[M1kEC]

Thanx I've just swapped panel over with a known good one an still does it so I'm inclined to say it's gotta be a wiring problem so I'm gunna try an bypass it see if that fixes it an then look to see were on loom has the problem