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Thread: MAF trouble?

  1. #1
    Join Date
    Oct 2010
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    colorado springs, co
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    2001 3.0 Z3 1996 Lexus

    MAF trouble?

    My grandson has had trouble recently with the following codes on his 2001 325xi.
    P0313
    P1349
    P1351
    P0174
    P0171
    P0102

    Not knowing a lot about how banks work in an inline 6, it seems to be lean from what I can gather. I started it up and it stayed mostly in Open Loop, occasionally going into closed loop- where the fuel trims were around 28 short term and 0 long term. You could see the short term work it's way back to zero where it would go back to open loop. Did this on both banks. I'm 68, just got out of the ICU at the hospital, and need all the help I can. I'm guessing a dirty MAF, inoperative MAF, or a split air housing going to the intake? Any other thoughts and am I aiming in the right direction. I've got his car at my house, and will only be able to work in short periods of time, so want to go after the most likely things first. I have a pick pull nearby, anyone know what year models I can pull the MAF off of if it turns into a bad MAF?
    Last edited by jaaa; 11-08-2018 at 11:51 PM.

  2. #2
    Join Date
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    2018 BMW M240i
    P0171 and P0174 are classic indication of vacuum leaks. At that age the rubber and plastic vacuum hoses are getting brittle. Go to www.bimrs.org to find a reputable indie shop that specializes in bimmers. Have the shop perform a smoke test on the intake. The leaks could be bad enough that the engine is misfiring. The P0102 code sez the MAF is under reporting. This again could be caused by vacuum leaks. Why? The engine computer (DME in BMWspeak) knows what the MAF should be reporting at certain engine speeds. The DME compares the “should be” value with what’s being reported. If there’s a large difference the DME will throw this code. As an example, a 2.5 liter engine, when idling, should be sucking in about 4 grams of air every second. That number will be lower when there are vacuum leaks. Basically, unmetered air (air that hasn’t be measured by the MAF) is getting into the intake. The DME knows about this because it’s receiving data about unburned oxygen in the exhaust from the oxygen sensors. The DME compensates by enriching the fuel/air mixture.

    The MAF is the most reliable part under the hood. They do fail, but rarely. If the MAF is bad make sure the shop installs ONLY a MAF made by Siemens/VDO. PERIOD. Siemens/VDO supplies MAFs to BMW. Aftermarket MAFs fail quickly.
    Last edited by MarcoZandrini; 11-09-2018 at 07:16 AM.

  3. #3
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    EXOTICS
    I agree with Marco,seems like intake leaks causing lean fuel mixtures,leading to misfires.
    One other possibility is low fuel pressure. Attach a fuel pressure gauge to the Shrader valve at the fuel rail,
    take readings at:idle-1500-2500-3500rpm. Post back with results.

  4. #4
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    Oct 2010
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    colorado springs, co
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    2001 3.0 Z3 1996 Lexus
    Just wanted to come back and give this thread some closure. I did some looking at utube video's that helped me solve this. It turned out to be a leaky intake runner gasket. My grandson couldn't afford a smoke check so we did this the hard way. Took it apart about three times before we figured out the aged gasket was leaking.
    Special shout out to the 50'skid for this video:
    https://www.youtube.com/watch?v=3encrkBsss0
    Last edited by jaaa; 11-16-2018 at 11:50 PM.

  5. #5
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    My grandson just brought back his car with missfires on cylinder 4 5 and 6. I took a look at it and it won't go into closed loop on bank two. I cleared the codes and it still wouldn't get into closed loop and the codes would come back. I checked the oxygen sensors and the bank two one wouldn't switch at all. Just stuck at around .4 volts while the other bank's sensor worked fine. I cleared the codes a few times, but the problem looked like it was a hard failure as the CEL light kept coming back on and it never would go into closed loop. I went to a junk yard and pulled the front oxygen sensor and installed it. Funny thing is, when I first started it up, it still wouldn't go into closed loop on that bank, but after a minute or two of higher revs(around 1500RPM) it finally went into closed loop and the oxygen sensor started swithing like normal. Not sure what happened on that first turn on, but I took it for a ride and all seemed to be well. I'm still wondering if I fixed it, and why it took so long to go into closed loop?

  6. #6
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    Delayed until cats get up to temp is my understanding.

  7. #7
    Join Date
    Apr 2013
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    2003 330cic
    You can build your own smoke tester for the e46 with a cheap transfer pump and a cigar. Do a search to find the video.

    It is likely you still have leaks. The code isn’t triggered until fuel trims exceed 10% but normal operating range should be +/- 2%. If you want to solve the problem:

    1. If the o2 sensors are original and over 120k replace them
    2. MAF doesn’t get better with cleaning. If it is under reporting then replace with Siemens VDO
    3. All the rubber is likely bad so you should replace SAP lines, two boots, and CCV. Also inspect DISA
    4. Test fuel pressure. Fuel filter interval is 60k, and pumps can fail at 100-120k

  8. #8
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    Let me add to the excellent advice from harrier. The fuel pressure at the fuel rail gas to be at leadt 50psi at all engine speeds and loads. Item #2 in the link is the cap to the fuel pressure test valve. http://www.realoem.com/bmw/enUS/show...diagId=13_0900. If the pressure is low the likely culprit is the fuel pump. The ONLY fuel pump you want to buy is a Siemens/VDO pump. Also, the fuel filter has the fuel pressure regulator. The only brands of filter you want to buy are Mahle and Keyser.

    The OBDFusion app for your smartphone or tablet is a great tool. You can buy it on both iTunes and google play. Go to E46Fanatics and search for threads on OBDFusion in which jfoj has commented. He’s the guru.

  9. #9
    Join Date
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    2003 330cic
    Get OBDFusion and cable. Here are instructions:
    https://forum.e46fanatics.com/showthread.php?t=1097893

    The funny thing with e46 is sometimes the more you know the harder it is to fix. You are analyzing the system thoughtfully, but you are facing an issue that so so so many people have already faced, and the process for fixing it is very well-established. Focus on the fuel trims - leaks will be more evident at low RPM than WOT. MAF is incredibly hard to diagnose. Folks just unplug it and say "The engine runs much better!" and presume it is the MAF.

    If you want a high-quality diagnosis, get your logs and post them on e46fanatics.com - JFOJ will help you out.

    It is usually 2 or three things. As I said above, the light goes on at 10%, and it is running out of spec much lower. So usually leaks, sensors, and fuel can combine, each contributing their part. Some folks do enough to get the LTFT below 10% and get the light off. But there are almost always multiple factors. And I believe, without any evidence to back it up, that the MAF is a part of the problem very frequently. These cars are old AF.

    Do the steps above provided it is not financially unfeasible. Monitor LTFT as you do it - takes some time to adapt - the last bits are likely not worth chasing, as one of the culprits can be a leaking diaphragm in the brake booster, and that is somewhat pricey and a gigantic PITA to change.

  10. #10
    Join Date
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    2001 3.0 Z3 1996 Lexus
    Thanks Harrier. I've really had two separate issues with this car and shouldn't have put them in the same thread. The lean condition on both banks was cleared up by replacing the intake runner gasket and the car worked well for five months until this new issue came up. The new trouble of a bank specific misfires did turn out to be a stuck(bad) oxygen sensor. He's driven it a week with no trouble. I'm 68 years old and just starting to find my way around scanners. And I'm sure glad I didn't include the two bad fuel pump failures he's had to really muddy the waters. I really appreciate all the comments of help I've received in this forum.
    Last edited by jaaa; 03-29-2019 at 01:14 PM.

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