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How bad do MAF's have to be before they trigger the CEL to come on?

I don't have any receipts from PO's showing MAF's and have 80k on the clock. No CEL but I haven't done the "test." I'm personally not a huge fan of the test because my rev's are climbing so fast at that point that I'd need to have someone else in the car to read the measurement otherwise I'll be taking my eyes off the road at WAY too fast of a speed; If I perform the test in 3rd gear I'm going close to 100mph afterall. Moreover I don't have too many places where I can really open it up like that without being nabbed.
 

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There's no answer to that... the additive and mulitplicative adaption values will begin to run opposite of each other as the MAF's go bad. Once the adaptive values go beyond the allowable limits the CEL will get thrown. From personal experience you see a marked reduction in performance even before the CEL comes on.
 

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There's no answer to that... the additive and mulitplicative adaption values will begin to run opposite of each other as the MAF's go bad. Once the adaptive values go beyond the allowable limits the CEL will get thrown. From personal experience you see a marked reduction in performance even before the CEL comes on.
+1.

The dynamic MAF test is a pretty reliable indicator. 2nd gear will hit redline quick, but you can sneak a glance just before you hit redline. Even if you miss by a couple of hundred revs, you should have a ballpark number. 3rd gear is better, but understandably not always easy to find the room to stretch out the beast.

Regards,
Jerry
 

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Interesting stuff! New to the test features.
 

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Are the allowable limits due to external conditions or specific to engine and or set up. Sorry of I missed this somewhere else in the thread.
 

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Are the allowable limits due to external conditions or specific to engine and or set up. Sorry of I missed this somewhere else in the thread.
Yes minor corrections due to air density, temperature etc are compensated for.
 

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How bad do MAF's have to be before they trigger the CEL to come on?

d.
There is an answer:

REALLY BAD.


So if you are thinking 'just wait for the MAF cel before replacing', it is a bad plan.
 

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Agree having read this plenty, MAF's give little sign of being bad until replaced, when the owner thinks he has a new car. But no codes/lights to show it.
 

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Agree having read this plenty, MAF's give little sign of being bad until replaced, when the owner thinks he has a new car. But no codes/lights to show it.
That was the case for me, no cel but really poor performance. BMW could tighten the parameters but you get false triggers such as when you travel to high elevation etc. Get them tested and be sure.
 

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I have been playing with something for the past few days. I am a bit skeptical of the maf test, only because I have a scanner that tells me the truth. What I have been up to is unplugging the MAFs and doing the test then plugging them in and repeating. It is not telling me much because I have newish MAFs. I would expect that on a car with weak mafs you would see a difference between the two readings. If you were just comparing readings you would not have to get to 105mph to complete the test. As long as the test is done the same you could go to 5000rpm in 3rd and repeat.
I was wondering if there is anyone who has bad MAFs who would try this. At your own risk, and you should have a scanner to clear the codes you will get. I am not sure what not having the air temp does to the system. It may use values that play a big role in the output from the OBC which would make the comparison irrelevant.
 

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I have been playing with something for the past few days. I am a bit skeptical of the maf test, only because I have a scanner that tells me the truth. What I have been up to is unplugging the MAFs and doing the test then plugging them in and repeating. It is not telling me much because I have newish MAFs. I would expect that on a car with weak mafs you would see a difference between the two readings. If you were just comparing readings you would not have to get to 105mph to complete the test. As long as the test is done the same you could go to 5000rpm in 3rd and repeat.
I was wondering if there is anyone who has bad MAFs who would try this. At your own risk, and you should have a scanner to clear the codes you will get. I am not sure what not having the air temp does to the system. It may use values that play a big role in the output from the OBC which would make the comparison irrelevant.
lack of air temp will kick off a cel if you unplug the MAF you'll get maf and intake air temp errors - What scanner tells you the truth and how does it do it? Is it giving you running values?
 

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I have been playing with something for the past few days. I am a bit skeptical of the maf test, only because I have a scanner that tells me the truth. What I have been up to is unplugging the MAFs and doing the test then plugging them in and repeating. It is not telling me much because I have newish MAFs. I would expect that on a car with weak mafs you would see a difference between the two readings. If you were just comparing readings you would not have to get to 105mph to complete the test. As long as the test is done the same you could go to 5000rpm in 3rd and repeat.
I was wondering if there is anyone who has bad MAFs who would try this. At your own risk, and you should have a scanner to clear the codes you will get. I am not sure what not having the air temp does to the system. It may use values that play a big role in the output from the OBC which would make the comparison irrelevant.
I don't know the answer, but I don't think that works. Until the MAF is under full duress, it will appear to work fine. BMW uses a static test, and they never find anything wrong until it triggers a CEL. But under WOT at redline, the MAF is required to perform at its limits. That is where it will fail.

Remember, BMW had these under the maintenance plan, no wonder they weren't anxious to replace these on their nickel...........

Regards,
Jerry
 

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I have been playing with something for the past few days. I am a bit skeptical of the maf test, only because I have a scanner that tells me the truth. What I have been up to is unplugging the MAFs and doing the test then plugging them in and repeating. It is not telling me much because I have newish MAFs. I would expect that on a car with weak mafs you would see a difference between the two readings. If you were just comparing readings you would not have to get to 105mph to complete the test. As long as the test is done the same you could go to 5000rpm in 3rd and repeat.
I was wondering if there is anyone who has bad MAFs who would try this. At your own risk, and you should have a scanner to clear the codes you will get. I am not sure what not having the air temp does to the system. It may use values that play a big role in the output from the OBC which would make the comparison irrelevant.

Ding, ding, ding.

I had a wacky idea at one point and juryrigged a 'flow bench' using an old leaf blower and some 3" PVC pipe to try and create known flow rates.... The idea was to create a repeatable flow, somehow quantify this, then test new mafs to establish a baseline calibraton (ie 4.76 Volts at 450CFM) to allow us to evaluate MAFs.

Life intervened.

A
 

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Yes my scanner gives me live data. I know you throw those codes that is why I said whoever might try this should have a way to clear codes. The question is with temp missing what map is it replaced with?
 

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I don't know the answer, but I don't think that works. Until the MAF is under full duress, it will appear to work fine. BMW uses a static test, and they never find anything wrong until it triggers a CEL. But under WOT at redline, the MAF is required to perform at its limits. That is where it will fail.

Remember, BMW had these under the maintenance plan, no wonder they weren't anxious to replace these on their nickel...........

Regards,
Jerry
Good point you would have to take it to the max, that is what I have been doing. Again with new MAFs I sort of get the same numbers and maybe the difference is the temp being off.
 

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Ding, ding, ding.

I had a wacky idea at one point and juryrigged a 'flow bench' using an old leaf blower and some 3" PVC pipe to try and create known flow rates.... The idea was to create a repeatable flow, somehow quantify this, then test new mafs to establish a baseline calibraton (ie 4.76 Volts at 450CFM) to allow us to evaluate MAFs.

Life intervened.

A
Interesting you mention that. A few years ago I was working on a problem of radon gas in basements. One of the tools I used was maf hooked up to a sewer drain to measure the rate of flow. Interesting enough when I asked for the tool to be created, an engineer was using a leaf blower to calibrate the maf. I thought he was a bit wacked but it worked perfect. Maybe you missed your calling "ard engineering technologist". It is exciting for those with inquisitive minds.
 
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