Rev Limit 4000

[4638jay]

93 318is m42 engine that rev limits at about 4100, showing code knock sensor #1 (1225). 

Would this be causing the car to go into a limp mode, limiting it to ~4000 rpms?
Or is the knock code more likely a symptom than the cause?

[Tgoode318]

No it is not cause enough alone to make the car go into limp mode.

[4638jay]

If a previous owner swapped the instrument cluster with one from a 325, would it cause the RPMs to be off?

EDIT: Revs go up to 6500 on the instrument cluster printout, so I don't think this was related.

[4638jay]

I got a better look at the tac last night, the rev limit occurs at 4500 not 4000, does this point to a problem with the differential speed sensor and instrument cluster?

[Tgoode318]

Your best bet is to get a copy of the bently manual for you cars year and get a multimeter to test all of your sensors; the one your mentioned is a possibility but other possibility's include but are not limited to a crank sensor a cam sensor or even worn cam lobes *god forbid*. Is this problem in neutral or when driving? Or both?

[colin86325]

If a previous owner swapped the instrument cluster with one from a 325, would it cause the RPMs to be off?

Yes!
I had that exact problem with my M3.