M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Engine management => Topic started by: Asterian on May 12, 2012, 03:08:00 AM
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Hi everybody.
Yesterday took measurements of AFM Voltage output (pin 2 and ground).
Looks like:
(http://f4.foto.rambler.ru/preview/r/592x349/4fae15b1-87a5-df8c-aeda-7e4529718c2f/AFM.jpg)
In Values:
RPM U(V)
0 0,25
800 0,88-1,0
1000 1,06-1,07
1500 1,4-1,43
2000 1,62-1,64
2500 1,8
3000 2,05
6000 4,25
Reference Voltage - constant. IGN - 4.7V, when running - 4.95 V.
Does anybody have an idea if its correct?
And the major question - on idle voltage constantly pulsating from 0,88 to 1,0 V. Can it be cause of unstable idle (pulsating 750-850 rpm)?
Thanks.
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I'm no expert, but that looks like what I've been told it should. I'd say that's good enough for the computer.
In my experience a pulsating idle tends to be a dirty ICV or a vacuum leak in the intake system.
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I'm no expert, but that looks like what I've been told it should. I'd say that's good enough for the computer.
In my experience a pulsating idle tends to be a dirty ICV or a vacuum leak in the intake system.
Thanks.
ICV was cleaned with carbcleaner, but if I would have a chance - will try to check with surely working one.
Vacuum leaks - I found just 2 small cracks on vacuum hoses - was temporary fixed with silicone.
Would like to add - Idle 750-850 - can presume, cause tacho showing just 800, but per engine sound constant change I'm sure that rpm drops/increases.
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I've noted that many M42s are somewhat noisy and rough-running, at least as far as BMW goes. I also have other theories, but I have no real proof for any of them. The first is the AFM resistor tracks and air leaks. As that resistor media wears out and the tolerances open up a bit, the DME gets inconsistent signalling and RPM wanders like that.
Secondly, M42s tend to be just as noisy as high-mileage VW & Toyota motors and a bit quieter than equivalent Hondas. I think it has something to do with the chain drive and high frequency vibration transmitted via worn hydraulic motor mounts.
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Your AFM output curve looks fine.
The M42 runs rough. If the tach needle isn't moving up & down, you are fine. When people have issues with vacuum leaks, the O2 sensor & the ICV, they are usually seeing RPM swings of +/- 100 RPM or more. If you really want to be sure of the AFM, all you need to do is open the cover & move the two little copper contacts a fraction of a millimeter so that they are wiping on a fresh part of the carbon track. You can clearly see where the track is worn and easily move the contacts to a little to get them out of there. Unplug your battery to reset the ECU, and you would be good to go. It is probably unnecessary, though.
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Thanks for advice. Probably I will live it like it is.
Just interesting - if we'll have AFM in 100% working condition - will voltage be constant on idle..
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Yesterday made test to look inside AFM when can is running at idle. In fact AFM "spade" was twitching with 2-3 mm amplitude. For sure it causes voltage change.
But question again - is this twitching normal?
Means unstable air flow (which probably normal)
or maybe something wrong with return spring...
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How fast was the wiper twitching?
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Relatevely "fast". Maybe few "movements" per second.
..designed to prevent vibration of flap.. - seems not fully preventing.
Will be great if somebody can have a look how it is on his engine.
(http://www.m42club.com/forums/picture.php?albumid=206&pictureid=1276)