MAF Don't last long

[Dicky]

Been reading a bit about the MAF since my pal,s 330d bmw unit seems to be causing him problems. He had a crash a couple of years back and suspects the Bosch mass flow fitted at the time may be hampering his cars performance.

Anyway I read that these devices don't stay in calibration very long, typically as low as 30K miles which surprises me, the air flow sensing device apparently operates at around 200 deg C and deteriorates over time. Since they can adversely affect performance, consumption etc I was wondering if anyone can confirm or add to this or has a means of checking calibration.

Oh and their not cheap to replace!!

[Apex]

Most modern MAF's do operate on a "hot blade" principal and the air passing over the blade is converted into a volumetric factor and very an intake air temperature reading. What I am commonly seeing on the latest Euro 5 and Euro 6 diesel engines is that the readings of air flow seem to remain "accurate" for a more than reasonable amount of time ie. 3 years plus (this is on machinery running in excess of 2500 hrs a year, but I am regularly seeing huge discrepancies in intake air temperature readings, often 20 degrees out of calibration.

During the Bosch training courses I attended for these engines we were explicitly told to never attempt to clean a MAF using brake cleaner or any other solvent based solution, these leave a coating on the blade once evaporated and as the blade heats up during operation it causes the blade to burn rendering its readings inaccurate. Another factor that can cause issues with them is water vapor in large quantities contacting the blade during normal operation. I've seen 3 instances of our machinery being pressure washed whilst the engine was running and water soaking the air filter causing it to tear and water passing over the MAF rendering it useless.

These hot blade MAF's are not without their problems but they are far more accurate than previous types used.

I'm starting to see more diesel engines now without MAF's and manufactures opting to use MAP (manifold absolute pressure) sensors and a separate intake air temp sensor in the induction trunking instead.

 

The easiest way to check the calibration would be using a decent diagnostic system and checking the air temp readings against ambient air temp. Check the air flow rate usually displayed in Ltr / hr or Ltr / min and then calculating against the engine speed

[Tricky-Ricky]

In order to check a MAF, you would need to be able to reference the std calibration figures/scale, I have never seen them in any manual, just idle and WOT figures on other Nissan's, so kind of difficult to check for the average owner, unless you can access the std ECU, and log load vs voltage output.

 

Must admit I have never come across a problem with the MAFs on the few aging cars I have owned with a MAF.

Edited May 6, 2016 by Tricky-Ricky

[Dicky]

Most modern MAF's do operate on a "hot blade" principal and the air passing over the blade is converted into a volumetric factor and very an intake air temperature reading. What I am commonly seeing on the latest Euro 5 and Euro 6 diesel engines is that the readings of air flow seem to remain "accurate" for a more than reasonable amount of time ie. 3 years plus (this is on machinery running in excess of 2500 hrs a year, but I am regularly seeing huge discrepancies in intake air temperature readings, often 20 degrees out of calibration.

During the Bosch training courses I attended for these engines we were explicitly told to never attempt to clean a MAF using brake cleaner or any other solvent based solution, these leave a coating on the blade once evaporated and as the blade heats up during operation it causes the blade to burn rendering its readings inaccurate. Another factor that can cause issues with them is water vapor in large quantities contacting the blade during normal operation. I've seen 3 instances of our machinery being pressure washed whilst the engine was running and water soaking the air filter causing it to tear and water passing over the MAF rendering it useless.

These hot blade MAF's are not without their problems but they are far more accurate than previous types used.

I'm starting to see more diesel engines now without MAF's and manufactures opting to use MAP (manifold absolute pressure) sensors and a separate intake air temp sensor in the induction trunking instead.

 

The easiest way to check the calibration would be using a decent diagnostic system and checking the air temp readings against ambient air temp. Check the air flow rate usually displayed in Ltr / hr or Ltr / min and then calculating against the engine speed

 

I don't suppose the early Z's would have this Hot Blade arrangement. Mine looks like a thermistor mounted in the middle of the air flow tube, so I assume this type is more likely to suffer calibration drift?

My mates BMW has a strange looking arrangement. It has what looks like a thermistor mounted to one side of the air flow tube, and more towards the centre is a structure (can't as what it is) and has a centrally mounted and angled air inlet grill mesh.

Any idea what that could be?

[Tricky-Ricky]

Most modern MAFs are hot wire,and the DE is no exception, but there are other variations,so your mates BMW could be a membrane type, but there is also laminar flow, Karman, moving vane, and cold wire sensors, older BMW and VW used to use Karmen , and moving vane types.

 

Hot wire is usually used in conjunction with an air temp sensor to determine volume density, most use a 0-5V signal, but some use a frequency output form a film rather than a wire, As I said I have yet to own a car where the MAF has failed, or has exhibited symptoms of incorrect airflow signal due directly to the MAF itself, so not sure why your worrying.

 

 

Edit, just found these which may help.

https://www.oscium.com/sites/default/files/MAF_autoshop101.pdf

http://www.knfilters.com/MAF/MAFDevices.htm

Edited May 7, 2016 by Tricky-Ricky

[glrnet]

OP, Don't think it's a known problem on here.

 

 

Sent from my Zed using Nangkang tyres front, RE040's rear

[Dicky]

I've heard that if you disconnect the MAF and you run the car, if the performance improves then you have a calibration problem.

 

Anyone confirm this or could it cause damage ?

[Tricky-Ricky]

Some older cars will run with no MAF signal because the idle control is handled by TPS signal and IAC valve, however it still wont always reveal a faulty MAF, and its not always any sort of calibration fault, usually the circuitry of the MAF.

 

I am pretty sure the DE uses the the throttle body IE the stepper motor to control idle, so if no MAF signal is detected the engine wont run, could be wrong, but in any case its wouldn't necessarily indicate a problem with the MAF, as in order to control fuel ratio its not only the MAF that's involved, its IAT and lambda signal too.

 

Why do you think you have a MAF calibration problem?

[Dicky]

Thanks Tricky. I don't necessarily think I've got a problem, it's just that when researching a possible MAF problem on my mates BMW I read an article suggesting that calibrations can go out as early as 3 yrs. My car pulls well enough but it's nice to be sure that everything's working ok.

[Tricky-Ricky]

You have to remember that with a diesel engine the fuel is pre determined by the ECU the airflow is secondary to this, and not primary like a petrol engine, and it will run without the MAF connected.

I am not anywhere near as familiar with diesel engines, even though I own one, but there are other factors that influence the diesel combustion process, the EGR valve is a major player in affecting performance.