New MAF Sensor - what an improvement

[Palfrem]

Hi all
Not sure if this the right location, but..................
Last week had some problems with 2001 E320 cdi @ 95K miles
Usually goes like a train, but for some reason very sluggish, almost like the brakes are on.

Then later, pulling away the car would not rev beyond 3000. Cruised at 75 (eventually) on the M6 for 100 miles to home, but all not well. No "malfunction" info showing though.
A quick trawl of the posts on here and it seemed a fair bet that the MAF sensor was U/S.

Sure enough, diagnosotics confirmed vode for one dead sensor

So new MB part fitted and WOW!!!. What a difference, it seemed like thay had fitted a new engine not some sensor.

It's like the car is new, pulls really well, better changes, smoother and quieter even. My partner drove home from the pub last weekebd and she agrees how much faster it is. She inadvertantly lit up the ABS triangle away from the lights if you will!.

So, want a cheap tune up on a old oiler, get a new MAF sensor.

Cheers all
Mike

PS What exactly does it do??

 

[se97mlm]

The air mass flow meter (MAF) on a Diesel engine measures the amount of air flowing into the engine per cycle. This is used to verify amount of exhaust gas recirculated and to detect turbocharger surging (ie to protect it). It is also used in calculations at full load to determine the air fuel ratio, so that the mixture stays above 14.7:1 (black smoke limitation). At part load it is also used for black smoke limitation, although this time in relation to boost pressure.

There will also be an output to the gearbox to give an idea of driver demand, thus making the changes smoother. When the sensor is detected to be faulty, the ECU will enter "limp-home" which limits the torque and engine speed.

It's a complex part, measuring airflow in two directions, and correcting it for the air temperature (before the signal gets to the ECU) and on some applications the pressure too.

On a petrol engine, the mixture needs to be near 14.7:1 all the time, so the sensor checks the amount of air in to determine the fuel to inject. The Lambda sensor on a car with a MAF then double checks after combustion. ON a petrol car, the airflow in is a much more direct measure of desired torque output, so the sensor's failure on gearchange quality is more noticeable.

 

[SSBB]

www.autoshop101.com/forms/h34.pdf

Go to the above link for diagrams and explanations

 

[se97mlm]

Good Link!

The explanation is for a petrol engine though.

 

[Palfrem]

se97 - great explanation, thanks.
That would explain the black smoke I was generating as well

Cheers
Mike

 

[Dieselman]

one I prepared earlier

Strange this thread should crop up. I have stripped a MAF sensor tonight to have a proper look.
This one was not delivering full power and the thermistor was dirty. After a clean you can just see it's broken... Well it is now!!