I own an E30 with a M50TUB25 conversion for 2 years now. I really enjoy the car and I didn't have any real trouble. But 2 weeks ago I drove it in the morning, parked it near the metro station and left for work, everything was OK. In the afternoon, when I went to pick it up, a loud explosion-like noise came from the exhaust, under the hood. The engine started but there were misfires and less than 6 cylinders were working. As I diagnosed later 1 and 5 do not work.
The idle was rough and the engine did not rev unless the throttle was more than half open. Also, with wide open throttle, the revs would rise, but with occasional drops every one or 2 seconds, as if there was fuel cut off.
I had to return home, but when I drove normally, the car would go with 4 cylinders. When I opened the throttle wide open, the car would accelerate normally, with (almost?) full power.
I have already checked all 6 spark plugs and BREMI coil packs and they produce spark when not in place. The spark plugs are almost new.
I have disconnected the "Lambda" sensor but nothing changed.
I have disconnected the "MAF" but nothing changed.
I have disconnected the Throttle Position sensor but nothing changed.
I measured the resistance of the throttle position sensor and it was OK, according to Autodata.
The resistances of Intake Air sensor and Engine coolant temp sensor were OK also.
The 3 resistances of Idle control valve were a little lower from nominal (data avalable to anyone interested). The resistances of the Camshaft position actuator is a little lower than nominal too.
The resistance of the Engine speed sensor was 542 Ohm BUT it shold be 1152-1468 OHM, according to autodata.
Finally, I changed the coil packs for cylinders 1 and 5 with some Bosch ones, but nothing happened, the problem persisted.
All the hoses seem OK. No tears. Oil level is OK and it is clean. Coolant level is OK. Exhaust manifolds seem OK, no cracks. The only problen was a burn gasket just before the two exhausts become one.
On Sunday I will perform a compression test (just waiting for the gauge to be lent to me).
I do not know if the problem is at the injectors. I will measure their resistance tomorrow.
Has anyone of you seen or heard about such a problem? Do you have any suggestions what to check? I have not OBD-I scanned the car.