m20 not running well

[r0l4n]

Not always but often happens. When I rev up my m20b25 'til 5k rpms or so, it suddenly shuts off, like releasing gas pedal, and sometimes there's an explosion at the muffler, then I shift up and the engine runs ok again.

Does anybody experienced the same problem or could imagine what is the source of the problem? Thanks in advance.

[r0l4n]

Up!

[AdamF 88iS]

Similar symptoms were caused by the AFM on my car.

[r0l4n]

But, could the AFM change the ignition timing? I don't understand why those explosions happen :?

[Ryan Stewart]

backfires are caused by excess gas being reheated in the exhaust. If your afm is misreading and dumping extra fuel in it could cause that. Also if the signal is way off the DME is probably gonna shit itself, making your car die.

also, its not running well. well instead of good.

[E30godz]

a long shot but it could be a dead spot on the AFM slider...the door operates in a way that a contact rubs in a semi-circular direction across another contact that then feeds the signal to the computer depending on what location its at. you could try downshifting to a gear that will place you at a place higher in the RPM range and flooring it real fast and seeing if the takes off.

[r0l4n]

Well, it's not that easy to get another M20B25 AFM where I live. Will another m20 AFM fit my engine? I'm running motronic 1.3, 173 DME.

P.S. Let me change the post heading, sorry about my English, I'm trying to do my best :roll:

[uflnuceng]

On the left you can see the kind of board you have in your MAF



The little copper loop swings back and forth across the board as the vane-style flap open as more or less air comes in.

M20 AFM are cheap at salvage yards. Look on european eBay sites, call some salvage yards in your area and if they don't have one ask them to get it from one that does.

Any M20 AFM will do from an E30 (or maybe even an E28, early E34).

Kudos on the english by the way... its better than most American members of R3V ;)

[r0l4n]

So any other m20 AFM would fit my engine... how much would you pay for it?

[r0l4n]

And what about cleaning it? I could take the plastic firm off, clean the board and put the firm on again with some glue. Is it worth doing it?

[uflnuceng]

And what about cleaning it? I could take the plastic firm off, clean the board and put the firm on again with some glue. Is it worth doing it?

They typically go for between $50-75 US from a salvage yard.

I would atleast take off the cover and inspect the circuit board to see if the band has worn off or something. But there isn't much you can about it if it is, but it might save you some cash if there isn't anything wrong with it.

[r0l4n]

OK, I'll try to take a look inside. Maybe some cleaning would help.

Thank you all very much, specially uflnuceng for the pics and explanation. I'll keep you up to date.

[arsevader]

This link has proved to be very helpful for a lot of people.

http://frwilk.com/944dme/afm.htm

Down the page there is an interesting way to 'refresh' your AFM.

James

[r0l4n]

Amazing link! Thanks.

I've followed the instructions and got my AFM refurbished (moved the wiper south). Time to test it. I'll post results as soon as I had taken the car for a "walk".

[r0l4n]

I've tested my car for only 20 minutes and revving up only in 2nd gear, but the failure just dissapeared :twisted:

I'll have to test it further and longer anyway, in longer gears and in other conditions. I'll keep you up to date. Thanks a lot.