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Old 05-27-2010, 08:27 PM   #1
krauseda
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MAF Sensor Test

Does anyone have a DIY for testing a MAF sensor in a 2000 BMW 3232i? I have very poor acceleration with this car and believe this may be the problem.
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Old 05-27-2010, 09:53 PM   #2
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Have you thrown any codes?
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Old 05-27-2010, 09:57 PM   #3
wonglynn2004
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confused....will a bad MAF cause poor acceleration? why
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Old 05-27-2010, 10:08 PM   #4
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^ Because it controls the fuel/air mix in the engine?
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Old 05-27-2010, 10:14 PM   #5
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I have had poor acceleration for a couple months, and it finally and consistantly kicked out the following codes yesterday...
- P1397 cam shaft position sensor.
- P0101 mass or volume air flow circuit range performance problem.
I replaced the exhaust side cam position sensor and cleared the codes...no new codes have appeared.

The reason for suspeting a bad MAF is that I got a P0101, and when I disconnect the MAF, my 0-60 time decreases by 2 secs. I am not rushing to the dealership to spend $300 for a MAF because I haven't come across an article where a defective MAF will cause acceleration problems; it idles fine and is not misfiring.

Please let me know if I should be looking at something else.

David
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Old 05-27-2010, 10:17 PM   #6
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volumetric efficiency. I posted the link to download the tool and how to use it
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Old 05-27-2010, 10:30 PM   #7
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My maf is apparently bad, the engine light keeps going on and off. The dealership said it's malfunctioning. My acceleration has not been effected since it started throwing a code for it...weird. That's why I haven't changed it lol.
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Old 05-27-2010, 10:53 PM   #8
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simple yet effective test....

If it is a bad MAF you will most likely have a shitty idle....

Test for a bad MAF: Unplug it, drive around for a bit and see if the car performs better. If it does, bad MAF. If not, then there's another problem...


And before the thousands of don't do that it'll F^ your car post come in. Your car runs off of redundant systems. A.K.A. it is designed to run off of the map sensor in the event the MAF fails. I wouldn't recommend leaving it unplugged for more than just this simple test but that's because a bad MAF is better then no MAF
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Old 05-28-2010, 09:57 AM   #9
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My idle is fine but the acceleration is really bad. I'll try the MAF test mentioned above this weekend and see if it tells me anything.
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Old 05-28-2010, 10:21 AM   #10
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Have you tried actually cleaning the maf? Mine fouled out before and I picked one up from the junkyard for like 50$, cleaned it, and been fine ever since.
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Old 05-28-2010, 10:25 AM   #11
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Quote:
Originally Posted by Bondga View Post
simple yet effective test....

If it is a bad MAF you will most likely have a shitty idle....

Test for a bad MAF: Unplug it, drive around for a bit and see if the car performs better. If it does, bad MAF. If not, then there's another problem...


And before the thousands of don't do that it'll F^ your car post come in. Your car runs off of redundant systems. A.K.A. it is designed to run off of the map sensor in the event the MAF fails. I wouldn't recommend leaving it unplugged for more than just this simple test but that's because a bad MAF is better then no MAF
so much wrong with this info I don;t know where to start. BMW DOES NOT use a MAP sensor. Disconnecting the Maf does put it into know values but that does NOT tell you if the Maf is the issue
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Old 05-28-2010, 10:46 AM   #12
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Originally Posted by krauseda View Post
My idle is fine but the acceleration is really bad. I'll try the MAF test mentioned above this weekend and see if it tells me anything.
I feel you krauseda. I'm on the same boat and I dont really know why. My idling is fine but when i press pedal, seems like it's slow..
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Old 05-28-2010, 12:06 PM   #13
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Bad acceleration could also be a vacuum leak? Have you checked your intake boots and do you get any whistles under hard acceleration.
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Old 05-28-2010, 12:22 PM   #14
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so much wrong with this info I don;t know where to start. BMW DOES NOT use a MAP sensor. Disconnecting the Maf does put it into know values but that does NOT tell you if the Maf is the issue
MAP... No MAP, it's irrelevant. However, it does use a redundant system to run the car in the event tha MAF dies. If the MAF is bad and you disconnect it it will run off of the preset values in which the car will run much better if the MAF is the only problem... It will not tell you if the MAF is dead, only if the MAF is failing. If it's dead then it is already running of the preset curve and disconnecting the maf will do nothing

OP: If your Idle isnt bad I highly doubt your MAF is bad but you can check it just to rule it out. Bad Idle is generally associated with a failing MAF
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Old 05-28-2010, 12:35 PM   #15
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Quote:
Originally Posted by Bondga View Post
simple yet effective test....

If it is a bad MAF you will most likely have a shitty idle....

Test for a bad MAF: Unplug it, drive around for a bit and see if the car performs better. If it does, bad MAF. If not, then there's another problem...

And before the thousands of don't do that it'll F^ your car post come in. Your car runs off of redundant systems. A.K.A. it is designed to run off of the map sensor in the event the MAF fails. I wouldn't recommend leaving it unplugged for more than just this simple test but that's because a bad MAF is better then no MAF
Nope bad info. I really hate it when people say disconnecting the MAF will troubleshoot its possible failure. This is not the case. Regardless of if your MAF is good or bad, disconnecting the MAF causes the ECU to use the TPS and default fuel maps. These maps are defaulted to enriching (don't want to lean out) the air/fuel mixture and that's why your idle (or acceleration in this case) will (inevitably) improve. Other parts that can cause the same symptoms will be covered up by what you perceive to be as a bad MAF when that is not the case. I mean this method worked back in the days of E30s but today it doesn't really work.

Our cars don't even have MAP sensors btw

Pretty much, everything Seth said
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Old 05-28-2010, 12:46 PM   #16
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MAP... No MAP, it's irrelevant. However, it does use a redundant system to run the car in the event tha MAF dies. If the MAF is bad and you disconnect it it will run off of the preset values in which the car will run much better if the MAF is the only problem... It will not tell you if the MAF is dead, only if the MAF is failing. If it's dead then it is already running of the preset curve and disconnecting the maf will do nothing

OP: If your Idle isnt bad I highly doubt your MAF is bad but you can check it just to rule it out. Bad Idle is generally associated with a failing MAF
Continue to believe what you want. I tend to post facts and proper testing. But hey if you don't want to listen not really my issue.

The internet is full of so much wrong information its funny.

There are 4 cars in the shop right now that "The Internet" diagnosed guess what 1 of the 4 was correct the other ones now have alot of expensive parts installed, till they brought it to me.
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Old 05-28-2010, 01:03 PM   #17
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My method may not be the best most technical way to do it. But most people don't have acesses to the equipment needed to run a ful diagnostics. You may not like this method, you may not think it will work. That is not my problem. I have used it on two cars, with sucsess of diagnosing a failing MAF. However, I will state that these cars were dealing with rough idles as well as other factors. When the maf was unpluged and the car was cranked it idled fine. Plugging the maf back in yeilded a bad idle again. Thus, the maf was the problem.

I'm not trying to say that this is the best or only way to check a MAF but, for the average enthusiast, this is the only method I know of rather than paying a shop.

Finally, if my method is so wrong or useless why have you not posted the correct way. I don't doubt your skills as a mechanic i simply ponder upon the fact that you say I'm wrong yet provide no evidence of why. True I have provided no evidence that it will work other than past experience but the OP can test my method and yield a result (whether possitive or negative). However, you negate my solution and offer no path in return. simply is seem to be leading towards action where you seem to state do nothing.
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Old 05-28-2010, 01:08 PM   #18
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Finally, if my method is so wrong or useless why have you not posted the correct way. I don't doubt your skills as a mechanic i simply ponder upon the fact that you say I'm wrong yet provide no evidence of why.
I know I've already posted why your "method" is completely wrong. All you had to do was search through Seth's threads to find the correct way to test a MAF:

http://forum.e46fanatics.com/showthread.php?t=617788
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Old 05-28-2010, 01:21 PM   #19
Bondga
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I still won't say my method is completly wrong, however, I will say the method he posted is a better way to test.

I've used my method when a bad idle was present. Making the car rich wont make it faster or nessicarily help the idle.
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Old 05-28-2010, 01:33 PM   #20
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My first post in this thread said how to do it. I just said search As I posted the file and instructions and info on this before. You don't need any real advanced tools to check it right. Some of it can be done with a multimeter
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