e30 not starting/stays running...
 

Hello, I have a 1991 325i e30 (AT) that isn't starting/stays running.
Following most of the diagnostics that I've read so far with the symptoms of having the engine not turn over. so far I've swapped the fuel pump with a known working one and replaced the fuel and main relays with a new ones. The engine reference sensor is roughly 3-4 years old. Everything powers up and electronics work as normal. Its just the engine won't turn over or stay running.

The other day I first noticed something was wrong when driving about 30-40MPH at about 2-3000RPMs then having the engine choke and watching the RPM's drop to zero then back to normal like nothing had happened.

Today, I got the motor to turn over a few times after changing the relays with new ones, but when I would step on the accelerator, the engine would cut off. When cranking it for those first times, I could hear a subtle thump, like it was the fuel pump or something, not real sure.

I suspecting it to either be the fuel pump, fuel sending unit, dirty fuel filter, the engine reference sensor, or some electrical problems...
I'm going to swap the engine reference sensor tomorrow to see if that may be the cause of the problem.

Open to any tips or suggestions, Thanks in advance.

my bmw had a similar problem. the car would wanna start and nothing. i changed the fuel pump and filter and now it starts up just fine.

If you replaced the pump you need to do the filter as well.

More diagnosing...
 

Thank you for your help and suggestions.

When I got home, I went straight for the fuel filter and swapped it out.
Hoping for the best and trying to start the car, no luck.
After thinking it over some more, I checked the fuel regulator. When taking it apart, gasoline shot out like the fuel rail flooded. Reinstalling it with a new regulator, the motor had turned over right away, but when stepping on the accelerator the engine would die.

Coming up with new possible diagnosis, I'm think it might be the spark plugs, the distributor, or the coil pack. On the otherside it could be the mass air flow sensor.

Thanks again for any tips or suggestions. :D

The fuel rail should be full and under pressure. If it's now running at idle but won't accelerate, I'd be checking for leaks/tears in the rubber elbow after the MAF. Could be the MAF but if it will idle I wouldn't suspect the plugs, coil, distributor. Sounds mostly like an airflow metering issue or massive vacuum/intake leak. Those rubber elbows will develop cracks deep down in the bellows and you can't spot them unless you take it off and look, engine might idle but when you hit the gas, the engine moves and opens up the crack. Also make sure the clamps at both ends are secure, once you eliminate that there are other things to check if that doesn't fix it.

I changed the ignition wires and spark plugs with slightly used ones. The set of spark plugs that were originally on had a little oxidation to them. Did some simple tests just to make sure everything was running, checking the spark plugs for signs of fuel and checking them for spark. All checked out good.

One thing that was rather odd when testing, I believe the #2 spark plug, holding it to the frame to test the spark. The engine had started right up, with a good idle and with the throttle working without the engine cutting off. With the spark plugs back in, the engine wouldn't turn over. I had gone through all the spark plugs to test them and didn't get the same results. I'm thinking there might be some wear in the distributor and might be causing the hit and miss engine problems.

I'll have to check the air flow meter and hoses when taking a look at the distributor. I have an air flow meter on hand but not sure if it would be the same settings as a 325i since the one I have will be off a 89' 325ix. I would think they should be rather interchangeable.

Seem to be getting closer to the problem, she sure is getting a good tune up though...
heheh...

Thanks again~!..

Compare the part numbers on the MAF's to get your answer on that.

Are the plugs and plug wires OEM? If not, that causes problems. How old/how many miles are on the distributor/rotor? If you replace the plugs get STOCK OEM copper plugs. Platinums, multiple tips, Iridiums and the like did not exist when your engine was designed and they DO NOT improve performance in them. You need specially programmed engine management software and high output coils for them to make a difference, even then its negligible. Always run OEM in the ignition system of any car.

I still wouldn't be surprised however of you found a big leak after the MAF somewhere, or if in fact the MAF itself had problems.

All of the parts are OEM and off of the 325ix.
I swapped the mass air flow and still came out to be the same.

I'm not sure how many miles are on the distributor, but I took it apart to have a look. Had a fair sized wear on the pins with carbon deposit. The rotor was still in good shape.

I'll have to take a look at the intake hoses, I remember replacing most of the hoses due to minor splits on the ends when I first got that car 4+years ago.

Actually got it back together and running now.
I changed the engine reference sensor, the one that was on there had a pretty good ding in it. Probably from a rock or something...

Thanks again for all the comments and suggestions. :D