M50 B25 Backfiring, any initial suggestions?

[Rorty-corty]

Hello folks, I know I haven't posted on here much, if I has an E30 I would more often (and it's not for lack of wanting one) but I have a problem and am asking this boards vast knowledge for help. I'm having a problem with my trackday build 1991 BMW 525i

I started it this evening to move it and it backfired rather violently and then hunted around idle with the odd pop before stalling. It now does this each time I start it and throttle response it rubbish with it hesitating before it revs. This might possibly be due to an air leak caused by the initial backfire but the fact that it is continuing to backfire is my concern.

Any immediate ideas spring to mind? My brain is too tired to work right now (4 bad nights in a row thanks to unsettled young kids).

Cheers,

Rorty-Corty

[paulie30]

Hi, I had a 1991 M50 525i a few years back. It did a similiar thing. I replaced the airflow meter and ICV after having the fault codes read. It cured the problem.

[Rorty-corty]

Was the original problem your car had the backfire or the hunting idle? I think with this car the Backfire is the problem, the hunting at the moment I beleive is a side effect from the initial backfire blowing something off the inlet tract causing an air leak.

[paulie30]

The original problem was the backfire, probably caused by the AFM.

[Daf318is]

I've had a similar problem and just cannot cure it! I've changed nearly eveything so if you find a cure PLEASE tell me!!

[E30BeemerLad]

mine let a bit of a kick out of the air mass meter after it had been started a week or so ago, this was after i had put a £5 can full of fuel in an empty tank, so after a bit of running where it was ticking over like a dog due to the dodgy ICV and being parked with the nose in the air, it quickly ran out of fuel.

Sticking another £5 in had it behaving again.

Therefore, could these kicks out the inlet system and backfires be due to a fuel pressure problem?

[Rorty-corty]

Mine is low on fuel. The AFM is interesting though. Pity I haven't a spare to swap with. Unless the one on my 518 is the same.

[Brianmoooore]

First of all, check that the big air hose between the air meter and the throttle body isn't split, and/or any small hoses that connect to it or the inlet manifold haven't been blown off. In fact, check that the inlet manifold is still all there!
Apart from this, and in the absence of any code reading, the air meter would be my main suspect.

[Rorty-corty]

Well most fingers are pointing in its direction. I'll see if I can borrow one to try.

Cheers folks.

[mrLEE30]

back firing through the AFM is aslo caused by pushing the throttle when starting the car - injection cars do not need throttle on start up.

I am also going to say check the inlet side of the engine. with it running on idle spray carb cleaner around the inlet side, changes in engine pitch indicate an air leak where you sprayed. ((this stuff is volatile, do NOT spray anyewhere near the exhaust/spark plug area)

I am also tempted to say this is in the wrong section but seeing as you are mad enough to enter an E34 into a race series i am willing to let you off!!!

Good luck

[Rorty-corty]

Ta very much!

Thanks for the carb cleaner tip, I haven't heard or even thought of that one before.

[Brianmoooore]

Thanks for the carb cleaner tip

Almost any aerosol will do the job these days - the propellant is usualy LPG, since CFCs were banned.

[gareth]

vroooooom, the lynx effect