[Yozh]

So I had an old MAF kicking around and before throwing it out I decided to open it up. The way this one has failed was due to a temperature sensor failure. It was interesting watch the parameters jump from -55C to +17C or so while driving. Was a while ago and I do not remember all the details. Here are the pics, one under a microscope:






The connections are really thin. My theory as to why this one failed is on one of those 12 connections to the sensor measuring cell has burned out.

BMW describes it as follows: "An electrically heated sensor measuring cell (7) protrudes into the air flow (4). The sensor measuring cell is always kept at a constant temperature. The air flow absorbs air from the measuring cell. The greater the mass air flow, the more energy is required to keep the temperature of the measuring cell constant."

[bayerischer]

did u have error codes

[BB_cuda]

The air flow absorbs heat from the measuring cell .... You had a typo 😊

[Mark M]

Great thread and thank you for the tear-down.

I would agree with you, for whatever reason our MAFs are very sensitive and troublesome buggers.

I also have a spare MAF sitting in the cabinet. I bought my replacement through FCP Euro (Bosch Unit) and ironically ~12 months later the replacement began to throw codes. Engine responsiveness was also diminished. I used FCP's lifetime warranty, bought a replacement and returned the first for refund. Been about 9 months now and no issues.

To expand on your theory...I wonder if part of the premature wear on these is the way we drive. Follow me here....if the system calculates air mass based on DC energy required to maintain a desired temp regardless of air flow, those of us doing a lot of hard pulls will be forcing the MAF to 'energize' that little bugger quickly and often compared to those driving the car like a Camry. All these rapid heat cycles would definitely add undo wear and tear to the unit. Just a 2 cent theory.

Also....it is my opinion that MAF cleaner spray is actually bad for our setup compared to other setups that have the hot film visible in the air stream.

[TDIwyse]

Thanks Yozh.

Can you describe the process you used to remove the actual sensor portion from the OEM housing? If it wasn't destructive, would it be possible to buy a replacement sensor only, and re-install into the housing? Just curious if that would be less expensive than buying a "complete" OEM MAF unit.

[DWR]

Originally Posted by TDIwyse

Thanks Yozh.

Can you describe the process you used to remove the actual sensor portion from the OEM housing? If it wasn't destructive, would it be possible to buy a replacement sensor only, and re-install into the housing? Just curious if that would be less expensive than buying a "complete" OEM MAF unit.

Or install it into an alternative housing to get a "scaled" response curve, i.e. be able to measure more air. The DDE will compensation for some level of offset bias error via AFR readings. Better, a tuner could remap a new MAF curve. Hmm, another project ... maybe the last mod

[TDIwyse]

Originally Posted by DWR

Or install it into an alternative housing ...

Exactly what I was thinking :-)

Getting rid of that housing would free up some room on the intake routing...

[Len_Beach]

They can be removed from the housing if they're anything like the UK 330d with the N57.

I replaced my MAF and searched for the part number on the sensor itself. The unit was listed as a 740d from memory.

[TDIwyse]

Originally Posted by Len_Beach

They can be removed from the housing if they're anything like the UK 330d with the N57.

I replaced my MAF and searched for the part number on the sensor itself. The unit was listed as a 740d from memory.

Thanks for the response.

I'm not familiar with the 740d. Does it use a similar housing as the 335d for holding the sensor? Same type of connector?

If so, did you separate and remove the old sensor from the OEM housing, then replace with a new sensor within the same housing?

If so, how did you re-seal the new sensor/housing interface to have an airtight seal? JB Weld? Some other type of epoxy?

Do you have any information regarding how to remove the sensor portion from the OEM housing?

[rkstar9]

Excellent thread and cut out!

Originally Posted by Mark M

To expand on your theory...I wonder if part of the premature wear on these is the way we drive. Follow me here....if the system calculates air mass based on DC energy required to maintain a desired temp regardless of air flow, those of us doing a lot of hard pulls will be forcing the MAF to 'energize' that little bugger quickly and often compared to those driving the car like a Camry. All these rapid heat cycles would definitely add undo wear and tear to the unit. Just a 2 cent theory.

your theory sounds very plausible.

other questions that arise are:

1. would doing hard pulls after a cold start increase wear on heating element since the air would be colder?

2. would cold weather contribute to increased wear of the heating element?

3. would higher highway speeds increase wear in this element dis proportionally faster? assuming the air is very cold?

[Yozh]

Originally Posted by BB_cuda

The air flow absorbs heat from the measuring cell .... You had a typo 😊

That was a quote from BMW. Lol.

[Yozh]

Originally Posted by TDIwyse

Thanks Yozh.

Can you describe the process you used to remove the actual sensor portion from the OEM housing? If it wasn't destructive, would it be possible to buy a replacement sensor only, and re-install into the housing? Just curious if that would be less expensive than buying a "complete" OEM MAF unit.

Removal was very easy. The sensor is glued into the housing. I used a pick to break a tab that goes all around the mounting hole and then the sensor comes out. It also fits only one way as there is a locating tab. I would suppose if one can get a replacement sensor then it can be glued back in the existing housing.

[Yozh]

Just to add a few more comments on the above. I also wonder if a cleaner spray is actually bad for our MAF. I'm going to experiment and see if it "eats" into the potting compound. If it does I suspect it may eat into the area where those 12 fine leads are connected to the heated cell.

I did get SES a shirt while after I did my MAF cleaning and when I was coming out of work and gave it a bit more than usual before car was fully warm. Wonder if some of the theories above are correct.

Also, it seems all m57 MAFs are the same or similar.
The n57 ones are about twice the price and has a different connector. Not sure we can interchange them.

[Mik325tds]

Originally Posted by Yozh

Just to add a few more comments on the above. I also wonder if a cleaner spray is actually bad for our MAF. I'm going to experiment and see if it "eats" into the potting compound. If it does I suspect it may eat into the area where those 12 fine leads are connected to the heated cell.

I did get SES a shirt while after I did my MAF cleaning and when I was coming out of work and gave it a bit more than usual before car was fully warm. Wonder if some of the theories above are correct.

Also, it seems all m57 MAFs are the same or similar.
The n57 ones are about twice the price and has a different connector. Not sure we can interchange them.

Thank you for this thread Yozh!
I was wondering the same thing if the spray is maybe corrosive to the sensor or if powering up the MAF too shortly after the cleaning process would leave the sensor in a puddle of fluid requiring excessive power to bring up to temp.

As far as temperature cycles go, every one clearly introduces mechanical stress to the structure - eventually leading to micro tears and then corrosion.

[DWR]

There are actually multiple sensors surrounding the heating element, hence the multiple leads. The MAF can measure air in both forward and reverse airflow directions from the differential measurements of upstream and downstream sensors. That way it can account for pulsations that would otherwise be "counted twice".

There is also an intake air temperature sensor located in the MAF. It is an NTC, negative temperature coefficient thermister. The temperature is sent to the DDE as a PWM signal, integrated into the mass air frequency signal. So, the wild swings in air temperature are separate from the mass air sensing portion of the circuit.

[Miko226]

If only BMW would recall these sensors and reimburse us! These all fail on the D's its pretty wack.

[temporaptor]

Originally Posted by Miko226

If only BMW would recall these sensors and reimburse us! These all fail on the D's its pretty wack.

My maf on my X5 was replaced for free under this sib last year even though I was having no issues.

http://www.bimmerfest.com/forums/att...1&d=1502039404