M20B25 Harness swap

[Norrbelius]

I have a old modell m20b25 engine and after engine rebuild and harness ecu swap from a e34 the engine runs porly.
Bad idle, sound like missfiring somtimes at higher rpm. Jumps a bit when running at lower revs. But runs relatively good at full throttle.
The problem get worse as the engine warms up.

I´ve tried many things but don´t seem to get the end of the problem.

Sorry for my bad english.

[jlevie]

It is really hard to say what the problem here is. It really could be anything in the engine management or fuel systems. The bad idle could be intake leaks, a bad AFM, a fuel system/injector problem, a bad DME, ignition problem, etc. Misfiring at higher engine speeds could also be any/all of those. A smoke test will tell if there are intake leaks and fuel pressure checks will tell if there are problems in that area. After that you have to start swapping in known good parts to find the culprit(s).

[Norrbelius]

Ignition seems ok when you look at the spark, hard to say.
Injectors are good.
Intake do not leak.
Fuel pressure is little to low at 2,5 bar can that be bad for the idle. should be 3,0.

How do i get the rpm- and temp gauge to work?

[jlevie]

At idle rail pressure will drop to a bit over 2.5bar. If you disconnect the vacuum line to the FPR the pressure should go to 3bar.

[Norrbelius]

I´ve replaced the air flow sensor but with no success.
And running without pulse sensor on the spark plug wires shouldn't make such a big difference.