DIY MAF sensor testing?

[veedweeb]

Is it possible?

My '98 W202 C240 just doesn't feel right. It's not changing gear the way I would expect it to, and it doesn't pull like I think a 160+bhp car should.

Trouble is, I've had it since October, and it's not really any different than when I bought it. I mean I haven't noticed any deterioration as such.

It is covered by a warranty though, and I'd like to be able to go to the dealer and tell them (a) that there actually is something wrong with it, and (b) what it is...

I'm reasonably handy at spanner-twirling so I'm just wondering if there is a way of testing the MAF sensor, which is what I suspect to be at fault. Any ideas?

 

[Blobcat]

I cannot comment on testing the MAF electrically. However if the car is unwilling to rev beyond 3,000 and there is no kick down then the MAF is pretty much done for.

 

[veedweeb]

That's the thing though... it revs quite freely all the way to the redline.

It's reluctant to kickdown, and sluggish to change up (the revs raise in between gears). There's plenty of ATF and it's a nice sparkly red colour. The car has done 60,000 miles and I guess it wouldn't hurt to change the fluid, but that wouldn't solve the "flat" performance. Like I say though, it's flat when compared to what I think it should be like. It might be that my expectations are too high.

As far as the performance is concerned, if it were an older, less complicated car, I'd be looking at the acclerator pump diaphagm as being at fault, but obviously that doesn't apply to this car.

 

[RCLORLEY]

My Maf Sensor On My A Class Is Faulty, My Local Mercedes Garage Did A Mini Inspection For Free So I Could Identify The Problem. My Car Suffers Flat Spots , It Sometimes Pulls Away As Though It's In The Wrong Gear And Sometimes Slows When I Change Up

 

[Uncle Benz]

Sometimes MAF sensors don't throw up a fault code, but an independent with a scanner can read the live data stream. I have found that the WOT reading needs to be roughly 3 times the reading at idle. If it is lower the MAF is on its way out. I don't know of any way of testing this unit with a simple voltmeter, unfortunately.

 

[bibamus]

Try running it with the MAF disconnected for a few miles ( make sure ignition is off when you disconnect and connect the MAF.) It wont do any harm and might give you an idea if its faulty, ie if the car performs better, its a fair chance the MAF is faulty.
Allan

 

[veedweeb]

Try running it with the MAF disconnected for a few miles.

Right. I did that last night...

At low revs, when pulling out of junctions and so on, it's very hesitant and on the verge of stalling. However, about 1500 to 2000rpm, there's no real noticeable difference to with it connected.

To be honest, I'm not sure what that has proven?

 

[veedweeb]

Bit of an update...

I bought the car with a 12 month RAC warranty and the sensor was covered, so I managed to convince the garage that it was faulty and needed replacing under warranty. They did it this morning.

The difference is amazing. Before, it just wasn't right - but it wasn't so bad that I could be certain what was wrong.

Now, it's so much smoother, gear changes are better and it pulls like a train.

My faith has been restored. For now!