Possible MAF Problems ML 270

[Welshlensman]

Been having problems with the power on my ML for a very long time and nobody seems to have an idea what's going on. "Enough is enough. Lets just have a fiddle me thinks".

Anyway, I filled the fuel tank the other day and decided to totally disconnect the MAF plug to: (a) see if a dash warning light would illuminate. (b) see how the performance was affected. (c) Check if by doing this, there were fuel consumption differences.

(a) No warning light showing.

(b) Its now been disconnected for around three days and although the burst acceleration is much slower the gradual has not really been affected at all. In fact it seems a little 'smoother'.

(c) I usually get around the 130 - 140 miles between the full (up the filler tube) to the three quarters mark - I'm still getting that with the MAF un-plugged.

Afraid I'm not technically minded but does this mean something is wrong with the actual MAF or perhaps corresponding wiring? Is there normally a warning light? If there is a problem with the wiring, does anybody have a diagram of the colour codes from the plug to the ECU for reference.

Any help appreciated guys.

Thanks

 

[denchen]

I don`t know if it helps but my C270, I believe its a bit different to yours, anyway it started to loose acceleration and use more fuel. I got some proper MAF cleaner of ebay and cleaned the MAF sensor and fitted a new air filter. Motor runs like a dream again now and over 50 mpg again on longer runs

 

[E320C]

MAF

I don't how much it is for your cars but I just did my MAF sensor on my E220 CDI Estate 52 plate. £37 inc vat from e u r o c a r p a r t s. They are doing 31% off. I bought a pierburg one which is o/e. Part numbers matched my original pierburg MB one with the only difference being original had a MB badge on it.

Symptoms of my car was no power, not revving in gear over 2k and poor mpg with no warning lights. I checked the turbo and could hear the turbo and see the actuator moving.

After I changed the MAF, problems solved, smoother, faster and better mpg.

 

[Welshlensman]

Cheers guys but I've taken the MAF out of the loop so to speak with no apparent adverse affects, just the same lack of power on acceleration that I have when its connected. Iys almost as if its doing nothing when connected!
Is there supposed to be a warning light on the console if this thing is malfunctioning?

 

[oigle]

MAF failure often won't light the lamp. Your motor is obviously in limp mode. This can be caused by a number of things including the MAF. EGR issues, swirl flap issues etc.
Sounds like you have a crook MAF but you should check other issues too.

 

[The Pan Man]

OK Welshlensman, Here is my MAF test, It works everytime and has never failed me. Reconnect your MAF drive the car normally on a clear stretch of road accelerate foot down to the kick down point DO NOT KICK IT DOWN. As the car is building speed ever so slightly ease your right foot back 1/2" or so If the car seems to pick up a little then it's your MAF. BMW MERCEDES AUDI and RENAULT has been my personal experience all the same. Hope that helps.

 

[Welshlensman]

Thanks again guys. Will give that a try Pan Man and report the results as it might be relevant to someone in the future.

 

[Alex Crow]

OK Welshlensman, Here is my MAF test, It works everytime and has never failed me. Reconnect your MAF drive the car normally on a clear stretch of road accelerate foot down to the kick down point DO NOT KICK IT DOWN. As the car is building speed ever so slightly ease your right foot back 1/2" or so If the car seems to pick up a little then it's your MAF. BMW MERCEDES AUDI and RENAULT has been my personal experience all the same. Hope that helps.

Whilst this may work (often very well) for petrol engines, it does nothing to prove a faulty MAF on this diesel.
In truth, the MAF sensor on this car does very little, and the ECU can cope just fine without it (although it cannot monitor EGR flow and other subtleties, and may choose to use 'limp home mode' if its software dictates).
On petrol cars however, the MAF sensor values are highly critical to achieve correct A/F ratio (diesels care not, until it drops below 20/1 and we notice a little black smoke).

Is there really no way you can get the fault codes checked, as a starting point?
Without that, you really are going to struggle to get it right first guess.

 

[The Pan Man]

Alex, You have much more experience of these things than I do but it has worked for me on 2 Audi V6 diesels a Vauxhall Omega 2.5 Straight 6 diesel (BMW powered) and on my first Mercedes E240 Petrol. These were all my own cars and being an ex professional motorcyclist it's all about you knowing your ket and what it does and when it does it. The Omega also had a cracked turbo pipe at one time that slowed down almost to a stop.

 

[Welshlensman]

Tried your test Pan Man but virtually no difference in response. Thanks anyway.

Strange thing happened driving home last night though. Really fed up with this problem and sort of lost my cool a little bit. Getting onto a straight section with light traffic I literally stamped the throttle to the floor six or seven time in very quick succession, (activating the kick down button) after which the car worked brilliantly with full acceleration restored!! I tried this as she's not been giving any 'kick down' for some time, even got into trouble trying to overtake a lorry a few days ago and had to brake hard and pull back behind it!
Back to the same problem today, so I have very little hair to pull out now.

In response to your comments on codes Alex. My friend is a Professional Mechanic and he uses the star system. Tests show no fault codes and he's pretty much run out of idea's as to what the problem could be.

 

[Alex Crow]

In response to your comments on codes Alex. My friend is a Professional Mechanic and he uses the star system. Tests show no fault codes and he's pretty much run out of idea's as to what the problem could be.

You might ofmentioned that it has been checked with Star, and that you have access to Star.

I suggest you check live data now, particularly throttle position sensor values, boost and high pressure control - but really there are a zillion other things to check as well, if you have Star.

 

[Welshlensman]

Sorry Alex but thought I'd mentioned that the car has been checked on the Star system. I did request info on Indies recently so as to try someone else with that system. There appear to be two places local to me that I'm going to have to contact (probably after Christmas now) All my hard earned is going to be given to my relatives and their ever expanding families in the annual Christmas rip-off.