Mass Air Flow Sensor

Whoopitupinmo · #1 09-08-2008, 05:56 PM

HELP - Just replaced the MAF and now the car hesitates when accelerating. Any ideas!!!!! Are there any additional diagrams regarding vacuum leaks, not sure where to start

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cocoabrova · #2 09-08-2008, 11:27 PM

Are you getting a CEL or any codes (if you've scanned it)?

What was it doing prior to changing the MAF to cause you to replace it? Usually replacing a MAF is fairly straightforward- make sure ignition is off, carefully unplug MAF connector, R &7 R MAF, then re-install clamps/connector. You also should've got some kind of code/CEL that you'd have to clear before starting vehicle with the new MAF installed....

Whoopitupinmo · #3 09-09-2008, 05:57 AM

I will ask if he got codes after install. Prior to install we had the P0171 and P0174 codes. Too Lean in Bank 1 and Bank 2. Checked everywhere we could think of to look for vacuum leaks, but maybe we missed something there. The car runs perfectly fine with the old MAF installed but the codes put SES light on.

The car after the new MAF was installed felt like the gas peddle was "slow" and the car took a second before it would accelerate after hitting the gass pedal, only from a stop. The acceleration was fine during increasing speed at driving, just the issue at the initial acceleration. Seems like the car wanted to die out and then it would go, just a very slight hesitation in the gas peddle.

Thanks for your help. Look forward to the reply.

supersteve · #4 09-13-2008, 07:16 AM

Did you get any codes after the new MAF?

If not put the new MAF back in and recalibrate the gas pedal. The procedure is here in the article section.

http://www.xoutpost.com/articles/x5/e...-ms43-edk.html

It would be extremely odd for both of the banks to have O2 sensors go bad @ the same time. So then you have to look @ what can cause both banks to run lean. You have already looked for vacumm leaks with out any resolve. If the new MAF have caused different results I would suggest you start from there.

The computers can run in CLOSED LOOP or OPEN LOOP. If the parameters are within a preset range the computer goes into CLOSED LOOP. This means it partially goes to sleep. Everything is fine so it doesn't have to work.

Your computer has been trying to compensate for a problem, running in OPEN LOOP. In doing so it has made adjustments to it's "normal" parameters. It would make sense that the old MAF was sending a weak signal. This would in turn tell the computer, incorrectly, to give less fuel because there is less air. The end result can be the computer leans out the mixture causing the O2 sensors to,properly, set the codes you have.

There is always a "HOWEVER."

However, now that the new MAF is sending the correct information to the computer, the computer sees this new information and out of it's norm again. Now the MAF is telling the computer it's getting lots of air and we need more fuel so it continues to run OPEN LOOP. So, either until the computer re-adjusts or you change the parameter the computer has adjusted to compensate for the old MAF you will run a little rich just off idle. This rich off idle condition will give you a little stumble when you first hit the gas. Re-zeroing the gas pedal potentiometer (fancy word for a dimmer switch) may fix it right away.

Let us know.

SS

Whoopitupinmo · #5 09-13-2008, 08:08 AM

Thanks for the response Steve. We did not get any other codes with the new MAF in, however, we did not run it the length of time usually needed for the SES light to come on. Usually takes about 5 starts or 30 + miles before the codes would be thrown.

I will print it and have the boss look at it on Monday. I called the MAF supplier and he said I could return the MAF. We will try your suggestions first.

I always see you posts on here and it is a GREAT forum. We have been able to do so many things that would have cost a small fortune to take to the dealer. The car has 103K on it, great car, but I do realize at this point it will require some "higher" tech maintenance. We will try your post and I will update it when complete.

Thanks again for the reply, I do truly appreciate it.

swissfrank · #6 09-13-2008, 01:46 PM

i think you may have a vacuum leak, maybe something isn't connected properly, or is leaking now...

Whoopitupinmo · #7 09-13-2008, 03:46 PM

Have been looking for vacuum leaks, is there any diagrams or details on how to find a vacuum leak, we have searched and searched, don't seem to find any, Have replaced some of the obvious like oil seperator hoses and checked everything that is visible. Tried carb cleaner to rev RPM's to no avail also. Thanks for the replies

fernor · #8 09-14-2008, 11:38 AM

Hi, your problem is a common problem, you might have a crack on the air duct hose elbow, said part cost $15.00 dollars at the dealer and it is easy to change, however, you shoud have a sharp whistle noise coming from the engine if that is the case.

In most cases a leak from any hose will give you a different fault code that is not even related. For example, if you have some kind of oil leak, this could be from a broken line from the crankcase breather valve. However, this condition could throw you different fault codes like the crank case sensor or perhaps you would get the lights on for the ABS which is not even related to. Unfortunatelly, in this car once the computer DME gets other inputs that are different than a normal disfunction, it will give you unrelated codes.

If you like additional information, write to my email [email protected] and I will send you some pictures, my advised is thet you buy the BMW X5 Bentley book that is very helpful.

Weasel · #9 09-14-2008, 12:25 PM

I agree with what fernor just said. And for future reference, I have never personally seen a bad mass air give lean faults... it usually gives "mixture too rich, multiplicative values" for a bad mass air. You do have unmetered air coming into the system for the lean faults.

And for BMW's terminology; adaptive values are at idle. Multiplicative values are off idle, when driving basically.

Whoopitupinmo · #10 09-14-2008, 06:52 PM

OK - well now I am really lost. Original posts indicated a MAF sensor bad with the P0171 and P0174 codes coming up. Well, we will continue to look for leaks, I will have him check the elbow hose. The car runs great and mileage is around 16 which seems pretty good, probably could be a little better.

There is no whistle noise that I hear either. I will have him check the hoses more carefully again. Any other obvious locations for a vacuum leak he should look for??

Thanks again.

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