MAF sensor problem??

[kalsman]

Here is my car:
1991 525i automatic, 141,000mi

Here are the symptoms as described by me and my mechanic:
backfire through exhaust on acceleration
backfire through intake on acceleration
rough idle

Computer readout said it was a faulty MAF sensor so I replaced it...but I am still having the same problems...Any ideas?

...also, is anybody in need of a almost new MAF sensor? (apparently I have two good ones now)

[Toomas]

Sounds like ignition problem...
But then again i might be wrong.

[kalsman]

Thats what the mechanic first thought too...apparently he tested the ignition system and everything seemed to check out. He could be wrong though...it wouldn't be the first time! I think I would trust anybody on this site before I would trust anything else that mechanic tells me.

[632 Regal]

i agree on ignition, wires cap rotor plugs? what plugs are you runnin?

[kalsman]

I have no idea. I suppose that means I should think about getting new ones? If so, can you direct me to the best ones?

[kalsman]

well I just tried to take a look at the spark plugs but it seems I don't have the necessary tools to do so. Time to head to the auto store to buy some tools I guess!

[BillionPa]

sounds like something is wrong with the timing, start with distributor items and then the crank position sensor.

[kalsman]

well I just tried to take a look at the spark plugs but it seems I don't have the necessary tools to do so. Time to head to the auto store to buy some tools I guess!

So I just put in new spark plugs and it seemed to smooth out my idle. Still backfireing through the intake though...

[joshua43214]

An intake backfire can look like a MAf problem on a scan. This is why I always harp about trouble codes only being hints to prblems, not actual problems.

Backfiring can only happen if a valve is open during the combustion proccess, so you need to verify ignition components and timing before you move to anyting else.

[Toomas]

Take off the cap, look at the contacts, is there any black stuff on them?
Can you see that they are worn (if the surface is uneven then its worn)?
Buy a new rotor anyways, its cheap and atleast i cant visually tell if its ok or not.
It should take you like 30mins to take it apart and put back together.

[Espen]

there is no rotor on the M50 engine.

kalsman, you have the same problem as me.
I drive with my MAF unconnected as that seems to solve the problem (untill i get my hands on a new MAF)

[BillionPa]

forgot the M50s came out in 90, thought it was 93 for some reason, maybe that was the VANOS version.

check the resistance on all the ignition coils, if one or 2 are way off compared to the other ones, you probably found the problem.

I have heard instances of the air intake temp sensor throwing MAF codes, if you have never replaced it, you may want to.

if the coils are ok, and the coil boots check out, then its probably a timing issue, and the crank position sensor (12141726590 i think) could be borked.

also... check all the contacts for all sensors on the engine.

thats MAF, air intake, coolant temp, block temp, and crankshaft position.

if one came loose from vibration, or got some water in it, that would cause problems. if one of the sensor connectors is missing its little metal bracket, that is bad.

how old is your O2 sensor?

[kalsman]

Unfortuantely I tried that but it didnt help at all...if you're interested I can make you a good deal on a MAF...

[kalsman]

Thanks a lot for all the ideas. Seems I've got a lot of diagnostic work ahead of me!
I've had the car for about 2 years now and never had to do any work on it...I took it on a long roadtrip and it seems that ever since its been having troubles. I've never changed the o2 sensor. Is that an easy fix? Do you think that maybe I should take it in for a tune-up and have somebody with more experience take a look?

[Toomas]

o2 sensor should not cause backfire, usually it make the engine "chop" when you travel at even speed. Also you can just disconnect it and it should put the engine in limp home mode, the sensor is somewhere right behind the exhaust manifold.

[kalsman]

Thanks Toomas, I guess its not the o2 sensor then. Everything seems fine at even speed. Acceleration is the only time that it starts having problems...