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#1 (permalink) Old 05-17-2009, 10:06 PM
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Mass Airflow Sensor

My son just bought a 530I 1994 about a month ago. Started having problems yesterday. Started a little harder than usuall after work no power after starting, let it run a few minutes then was able to drive home. Today started ran a little rough and only about 15-20mph top speed. I've heard there are some problems with the MAF sensor, tried tappimg on it at idle and got no change. I unplugged it and the idle surged a little then smoothed out. I then drove the car, it was driveable with reduced power. Is this closed loop with a limit on power?

I'm downloading a Bently manual now. Just thought I'd ask the experts, Does it sound like the Mass Air Flow sensor is the problem? How much is a good price for one?

Thanks in advance,

James
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#2 (permalink) Old 05-17-2009, 10:54 PM
OMFG another one!?
 
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Fine idea to check the MAF, and a look at the fuel system may help; possibly a new filter for example.

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#3 (permalink) Old 05-17-2009, 11:30 PM
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After reading the manual some I looked at the intake some more, found the hoseclamp where the rubber portion of the intake meets the intake manifold lose and not sealing. I thought I had the problem, repositioned the rubber and tightened the clamp, no joy still runs like dodo with the MAF hooked up.

Do I have to clear the codes to make it run with the MAF hooked up again or should it run well again if the airleak was the problem even though the check engine light is still on? If I disconnect the MAF sensor does the system still read the other sensors and only replace the MAF sensor value with a "limp home" value? Or does it disregaurd other sensors when it goes into "limp mode"? The manual is not very clear on testing the MAF, it's not cheap, hate to replace iti if not the problem.

I'm a multi brand certified marine tech and have a fair amount of fuel injection experience, I just don't know cars that well.

Again Thanks in advance for any help,

James
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#4 (permalink) Old 05-18-2009, 12:12 AM
OMFG another one!?
 
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As far as I know, any correction should be recognized by the engine computer.

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#5 (permalink) Old 05-18-2009, 12:33 PM
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I left the adapter I need to check the fuel pressure at work so I can't look at it now. I got the code blinked out by the check engine light, 1212 O2 sensor.
No code for the MAF. 116K mile car. I'm now wondering if the fuel pressure has been a little low causing it to run a little lean would this set the O2 sensor code? I've seen a lot of US made cars lose the in tank fuel pump around 110K-130K miles. At least the BMW folks put an access panel in the trunk to get it if that's it.

Seems to me if the MAF sensor was reading far enough off to make the car undriveable it would set a code.

At this point looks like I can't do much till I check the fuel pressure.

James
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#6 (permalink) Old 05-18-2009, 02:21 PM
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Try the camshaft sensor ?

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#7 (permalink) Old 05-18-2009, 02:42 PM
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Also after fixing the hose did you reset the adaptive values as the car has tryed to smooth out the engine with a massive air leak. you can do this by disconnecting the battery and connecting the + and - Leads(Of the car not the battery) together for 5+ minutes....

If that doesnt work try unplugging the O2 sensors(yes this will set a code) and try it....

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#8 (permalink) Old 05-18-2009, 02:49 PM
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Quote:
Originally Posted by marti5 View Post
Try the camshaft sensor ?
What should I do to try this?

James
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#9 (permalink) Old 05-18-2009, 02:51 PM
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Originally Posted by AlpineSixAndSeven View Post
Also after fixing the hose did you reset the adaptive values as the car has tryed to smooth out the engine with a massive air leak. you can do this by disconnecting the battery and connecting the + and - Leads(Of the car not the battery) together for 5+ minutes....

If that doesnt work try unplugging the O2 sensors(yes this will set a code) and try it....
Didn't think of the "adaptive values" this I will try along with the o2 sensor unplug if the reset doesn't do it.

Thanks,
James
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#10 (permalink) Old 05-18-2009, 03:01 PM
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Quote:
Originally Posted by boatguya1 View Post
What should I do to try this?

James
The Camshaft sensor controls the fuel to the injectors, so if your lacking fuel to the injectors it will only run with what its provided with.......as for erasing error codes and reseting adaptations, that will not make any difference.

It may also be a lack of fuel supplied from the tank, when was the last time the fuel filter was changed, I change mine every 10,000 miles, it normally happens at inspection II.

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#11 (permalink) Old 05-18-2009, 03:13 PM
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Originally Posted by marti5 View Post
The Camshaft sensor controls the fuel to the injectors, so if your lacking fuel to the injectors it will only run with what its provided with.......as for erasing error codes and reseting adaptations, that will not make any difference.

It may also be a lack of fuel supplied from the tank, when was the last time the fuel filter was changed, I change mine every 10,000 miles, it normally happens at inspection II.
No idea on when the filter was changed, my son just bought the car. Where is the filter located? I might have to drive up to the lake for the adapter for my fuel pressure tester. I was expecting a test port. Changing the filter to establish a known good and a timeline for maint sounds like a winner.

Thanks

James
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#12 (permalink) Old 05-18-2009, 03:27 PM
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Found filter location.

James
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#13 (permalink) Old 05-18-2009, 03:49 PM
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Quote:
Originally Posted by marti5 View Post
as for erasing error codes and reseting adaptations, that will not make any difference.
.... It will return the car to the Factory settings and no longer will have the information stored to adapt for the old vaccum leak.... Did this to my 740iL Via a GT1 scanner and that car is alot smoother and idles better(and lowered the idle almost 160rpms) so don't say is won't do anything Resetting the adaptive values allows you to have a black slate to work with then after a couple mile you can read them and see how the car is trying to adapt to the problem(also clearing the codes allows you to see the hard codes when they come back without any past codes....) after clearing everything Drive the car and post what codes are being tripped.

So try it and see if it Positivly or negatively effects how the car runs If it runs worst then it is trying to adapt for a severe issue(plugged fuel filter plugged air filter vacuum leak ect.)

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#14 (permalink) Old 05-18-2009, 05:14 PM
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Originally Posted by AlpineSixAndSeven View Post
.... It will return the car to the Factory settings and no longer will have the information stored to adapt for the old vaccum leak.... Did this to my 740iL Via a GT1 scanner and that car is alot smoother and idles better(and lowered the idle almost 160rpms) so don't say is won't do anything Resetting the adaptive values allows you to have a black slate to work with then after a couple mile you can read them and see how the car is trying to adapt to the problem(also clearing the codes allows you to see the hard codes when they come back without any past codes....) after clearing everything Drive the car and post what codes are being tripped.

So try it and see if it Positivly or negatively effects how the car runs If it runs worst then it is trying to adapt for a severe issue(plugged fuel filter plugged air filter vacuum leak ect.)
It still ran poorly (pretty much the same) after the reset.

I've got a couple fuel filters coming to the local parts place, should be there in a couple hours. I pulled one of the filters off and after draining the fuel in it I could not blow through it except for a very little bit. Compared to other filters on EFI systems I've blown through I'd say it is clogged.

My son reluctantly admitted to running out of gas about a week ago, don't know if that's a contributtor in this problem or not.

Thanks for the help, I'll post how it goes.

James
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#15 (permalink) Old 05-18-2009, 09:01 PM
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Fuel filters didn't do it. Tried unhooking the o2 sensor and no luck. Runs best with MAF sensor unhooked.

James
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