Faulty MAF

[Murphy1138]

Hi guys , I have had another thread going here http://forums.mercedesclub.org.uk/showthread.php?t=109972 about gearbox/Accleration issues - Think i have got to the bottom of this with the help and the STAR diag.

Just a quick one, a faulty MAF should come up on the STAR check yes?

I say this as i have run my car at idle and disconnected the MAF and it made no difference to the running of the car and NO DASH CEL light lit up.

I would think it would change the running by disconnecting it?

I also have bad start up issues , the car tends to fire up and then conk out on the first go, then re-start and it idles all over the shop until I rev it up for a bit and it sorts its self out.

Going to do a plug change at the weekend and re-clean the MAF/throttle body - any other suggestions?

Thanks,
Murph

 

[television]

The MAF seldom shows up as a fault, but it can sometimes, though the MAF has nothing to do with the starting, I have known a case where the car started just fine but if you touched then throttle the engine cut out.

With poor or incorrect fueling the engine power can be down, this can affect the gearbox and gear changes when the torque of the engine is too low.

The MAF for your car if a Peirburg is only about £65

 

[BlackC55]

The maf can cause starting issues if very old. You will have a Bosch maf fitted to your car.

Disconnecting proves nothing at all. It will just log unessary fault codes. Live data is the key to finding this fault.

 

[television]

The maf can cause starting issues if very old. You will have a Bosch maf fitted to your car.

Disconnecting proves nothing at all. It will just log unessary fault codes. Live data is the key to finding this fault.

But the chances are if it is doing nothing it is U/S

 

[Benzworx]

A bad MAF can cause a number of problems and will not always show up on star
but from what you have said 99.5% it would be the MAF sensor and only replace with the Bosch unit not cheap copies from ebay

 

[Alex Crow]

I would say there are many possibilities here, and jumping for the MAF sensor with no data (eg live MAF values, self adaptation values etc) to fault it.

One thing that crops up a lot is the effect of cheap pattern fuel filters on fuel rail pressure, certainly worth a check of rail pressure if in doubt.

 

[television]

Equally one could measure the voltages on the MAF direct, that would also tell you if it is at fault

 

[Rockall]

"Just a quick one, a faulty MAF should come up on the STAR check yes?

I say this as i have run my car at idle and disconnected the MAF and it made no difference to the running of the car and NO DASH CEL light lit up."

No that is perfectly normal - it is known as 'Murphy's Law' !!!

Regards
Bill

 

[Alex Crow]

"Just a quick one, a faulty MAF should come up on the STAR check yes?

I say this as i have run my car at idle and disconnected the MAF and it made no difference to the running of the car and NO DASH CEL light lit up."

No that is perfectly normal - it is known as 'Murphy's Law' !!!

Regards
Bill

Note that a CEL (aka MIL) is not an indicator of the fault codes logged in the engine ECU - most codes will not put on the MIL/CEL

 

[SteveX]

I'd recommend unless the voltages are constantly way off of the mark not to solely rely on this method (reading voltages from MAF).

I checked the voltage on my MAF and it did not seem as stable as I thought it should be (although it rose and fell with RPM within tolerance there was noticeable spiking and irregularities in the voltage which made me question it).

This lead me to replace the MAF when it was not at fault - I found the brand new Bosch unit to do exactly the same!

I would say the voltage read only gives you a clue if the MAF has failed in the following way:

- No reference voltage or diminished voltage between pin 4 (live) and pin 3 (ground)
- Pin two is NOT showing close to 12v
- Pin 5 (output to ECU) is not showing an output, or the output is not rising and falling at all with RPM

If the MAF totally fails in one way or another and no signal is going to the ECU you will also notice your inside air temp gauge rocketing and your fan will likely be on 100% of the time.

I also don't believe a specific MAF error shows, normally it's other components that show symptoms relating to the MAF to help indicate a potential failure.

 

[Murphy1138]

update - I just went to eurocarparts and got a MAF for £80 and stuck it in.....

The car is like new all problems have gone, its responsive , kickdown is back and and I now have full throttle again

Thank you all.

 

[SteveX]

Good stuff glad you got it sorted