91 325I Misfire

[ianhagerty]

I am hoping someone is going to point me in the right direction.

1991 M20 2.5( manual), when cold it drives fine however once warm it miss fires between 2800 RPM and 4000RPM, outside of this it revs and pulls hard, No smoke, no oil and water mixing - it only happens when it is warm (even if you leave it in the sun)

As a matter of course i have replace the dizzy cap and rotor arm with BMW parts, however this hasn't improved it.

If you rev the car with it stationary or the clutch depressed, it revs fine- no miss fire, however with the engine underload and driving the wheels, it miss fires - which in my head rules out the MAF.

HELP!

[paultv]

Just as a precaution, measure the resistance of all your plug leads - should be 2K or something - but check they are all the same resistance - they have a carbon resistor in them at the plug end that fries and causes arching inside the cable, then strange misfires occur when hot....

Just to rule this out really.

Paul

[ianhagerty]

Thank you Paul will check!

[Mitchen]

I had the same symptoms when my crank position sensor went. Might be worth checking it hasn't come lose and been chewed by the belts.