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Old 09-09-2006, 07:53 AM   #1
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Default air mass meter problems

hey guys i just picked up a 88' 325i that had been sitting for a long time, i finally got it going with some problems with my fuel system which is now running fine but the air mass meter has been tampered. cylinder 6's fuel injector wasnt firing due to a clog which has now been fixed but the guy previous to me tried to recify the misfire by richining the mixture. the car is running so rich it fouls the spark plugs up after only a couple minutes. ive played with the mixture screw myself just to lean the mixture so my car will run smooth but i can tell the sensor is off tune and i dont have a Co2 sensor to measure the exhaust gas with to get it right.

is there a general rule of thumb to get it in the right position and also is it the further the screw on the mass meter is in the richer the car is? anyone got answers for me?
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Old 09-09-2006, 05:23 PM   #2
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i have never even seen the screw you are talking about. i know they are on the cars but where, no idea. i never have looked since the book said you can't adjust them.

did the other guy mess with the flapper tension spring under the plastic black cover for the afm?
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Old 09-09-2006, 08:18 PM   #3
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the screw is the co2 bypass screw which shouldn't cause problems.

check the AFM guts and whether the black lid has been opened. if opened check if there is barely any tension to close the flap against the stop, if thats the case then its been adjusted to richen it up and you can increase the tension abit. if it has not been tampered with then don't adjust it just test as as below

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

otherwise the rich mixture is caused from something else. Have you checked that you have the right size injectors and your fuel pressure is correct?
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Old 09-09-2006, 10:47 PM   #4
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yes thats the screw under the black cover. its a 5mm allen key and it has been tampered with to richen the mixture. which way to you screw it to lean the mixture out? i know you should never mess with that screw but the fool before me had no clue what he was doing and i have to try fix it
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Old 09-09-2006, 11:04 PM   #5
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hey digger thanks for the link, it helped to explain how the air flow meter works but not how to adjust the screw to a better operating position, do you think it would be better to buy i second hand one which is correctly calibrated and is not been played with.

i was thinking of replacing it anyway because on deceleration when the revs drop back down the car almost stalls before jumping back up to a normal idle, i thought it may be linked to a dying afm any way
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Old 09-10-2006, 07:29 AM   #6
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there is no way officially to adjust the mixture via the AFM. i wouldn't worry about the screw as it more of an emission thing at idle and wouldn't cause overly rich mixture. More than likely the AFM is on its way out or someone has touched the internal spring. Has the black cap been removed (evidence will be in the form of silicon around the edge)? Pull the AFM out and check the movement of the flap it should rebound and hit its stop reasonably firmly and stay there. If it doesn't stop against the stop the spring needs to be tightened.

Used ones aren't cheap or readily available.

There is a test on the link i gave to see if the meter is ok electrically (output voltage increases linearly with flap angle from 0-5v with an input of 12V).

Is your O2 sensor ok? It should be leaning the car out at light loads and cruise, what fuel economy do you get?

Is the fouling the only indicator that you may be running rich? Are you using the correct plugs?
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Old 09-11-2006, 04:49 AM   #7
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the car has new correct plugs in it and i know its running rich cause u can smell it in the exhaust, ive leaned it out as much as i can and its running smoother now but when u rev the car the revs still flux alot especially when not in gear. i found a place that sells second hand meters for $150 with a six month garantee and im hoping it might solve the problem. if it doesnt it could be my throttle position sensor but i really think its the air mass meter.

also i havnt checked this out yet but will my car have o2 sensors cause its import and runs with no cats

oh and i cant tell you the fuel effeciency cause like i said its an import thats not registered yet and i can only drive it around my parking lot,
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