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Old 01-30-2013, 02:50 PM   #1
texlnghorn
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What are the correct MAF readings/Is my MAF Bad?

Is there a good resource to help understand the correct MAF readings?

The reason I'm asking this is because I've been battling the p1188 p1189 CEL codes for almost a year and I have replaced most failure items (upper and lower boot because both had tears, ccv and 4 related hoses, valve cover gasket). I had it smoked today but no new leaks were detected. The mechanic I was working with is a friend of a friend and does not have BMW specific diagnositc tools but he says that he has worked on other BMWs and has replaced the MAF to fix these codes when there is no leak and all other failures have been addressed. Before I shell out $200+ for a new MAF, I'd like to know if my MAF is bad. I have an ElmScan OBD2 scanner and the OBDWiz software that I use to read and reset error codes. It will tell me the Long Term and Short Term fuel trims. But I'm not sure what I should be looking for to determine if my MAF is bad.

I've done some searching on this forum but I'm not finding what I need. Can someone educate me on what I should look for?
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Old 01-30-2013, 03:00 PM   #2
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First indicate the problem: p1188 and p1189 are pre cat leaks. Those tell you that there is excess oxygen in the exhaust.

Indications that a MAF are bad includes rough idle and weird surges for automatics. This is generally solved by taking out the MAF and seeing if the car runs better. Some people spray it with CRC MAF sensor cleaner. I wouldn't personally, but it can improve idle, some say...

Your MAF doesn't sound bad describing your problems. Some replace the MAF and get no improvement, some replace the o2 sensors and get no improvement. If you search through the forums some people replace the maf and it clears the codes. Its all hit or miss from what I read. Has he replaced the little elbow boot next to the ICV, seems to be common from what ive read. Any others have experience?
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Last edited by college46; 01-30-2013 at 03:04 PM.
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Old 01-30-2013, 03:01 PM   #3
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What are your fuel trims running both at idle and while cruising??

What does the freeze frame data show? Errors at idle or while cruising?
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

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Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

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Old 01-30-2013, 03:29 PM   #4
texlnghorn
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Quote:
Originally Posted by college46 View Post
First indicate the problem: p1188 and p1189 are pre cat leaks. Those tell you that there is excess oxygen in the exhaust.

Indications that a MAF are bad includes rough idle and weird surges for automatics. This is generally solved by taking out the MAF and seeing if the car runs better. Some people spray it with CRC MAF sensor cleaner. I wouldn't personally, but it can improve idle, some say...

Your MAF doesn't sound bad describing your problems. Some replace the MAF and get no improvement, some replace the o2 sensors and get no improvement. If you search through the forums some people replace the maf and it clears the codes. Its all hit or miss from what I read. Has he replaced the little elbow boot next to the ICV, seems to be common from what ive read. Any others have experience?
I thought the combo of p1188 p1189 indicates cycling between too rich and too lean thus throwing the fault codes. I thought it was an issue of reporting between the pre-cat o2 sensors and the MAF. Reading thru the forums, most find intake leaks which I have found in both the upper and lower boots post maf as well as the hose from the valve cover to the ccv. I found these leaks by smoke testing. I replaced the ccv and all 4 hoses. I also had an oil leak and replaced the valve cover gasket and vanos oil line. There are no more intake leaks with the last smoke test. My car would idle rough with the leaks (i.e. in the 550 rpm range) but now it is idling much smoother (i.e. in the 725 range). I reset the error codes but after about 40 miles of driving the same 2 error codes p1188 p1189 came back. What is the little elbow boot next to the ICV? Is that the little Y section on the lower boot? But like I said, there is no leak after smoke testing. The error codes appear after cruising around.

Since I have a USB scan tool I was hoping I could do some preliminary investigation of the MAF to rule it out.
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Old 01-30-2013, 03:40 PM   #5
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Originally Posted by jfoj View Post
What are your fuel trims running both at idle and while cruising??

What does the freeze frame data show? Errors at idle or while cruising?
I'm a newbie at reading the diagnostic data. So basically I need to look at the short term and long term fuel trim data for both bank 1 and bank 2 at idle and under what cruising speed? I hooked up the scanner this morning and I believe at idle the LTFT for both bank 1 and 2 was around 11.75 and the STFT for bank 1 was around 2.5. The STFT for bank 2 was alternating between +2 and -2. Once I get better readings I'll post back.

What should I be getting normally?

I get the errors after cruising around for about 40 miles of mixed city/freeway driving.
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Old 01-30-2013, 03:45 PM   #6
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JBEuro something had a good write up on testing MAFs.. i forget where it is..
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Old 01-30-2013, 04:01 PM   #7
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Originally Posted by E46Mango View Post
JBEuro something had a good write up on testing MAFs.. i forget where it is..
Found it. Thanks for the head start.

http://forum.e46fanatics.com/showthread.php?t=617788
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Old 01-30-2013, 08:43 PM   #8
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Just a caution on MAF testing.

I have not yet fully confirmed this, but I am starting to see some MAF's (unsure if they are OE/OEM or counterfeit) that appear to read properly at idle and may also pass a WOT MAF test, BUT they seem to be under reporting airflow during cruise/normal off idle situations with really high fuel trims and lean codes.

So just because your WOT MAF test may pass, this may not be a validation that your MAF is in fact good.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose fan switch O-ring - BMW #13621743299
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Old 01-30-2013, 08:52 PM   #9
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try cleaning it. my mechanic cleaned mine and it was okay for a while but then i had to change it in the end. the maf does make a big difference.
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