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air mass sensor voltage - (urgent)help please - C180K 2003

H

hopewer

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Joined
Oct 6, 2008
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6
Hi,
Not having a lot of luck tracing a fault (running very rich), no diagnostics on.

Indie thinks it might be air mass sensor, but before I blow another £200, I thought I'd check the voltage. Looks to be idling at about 0.67v, 3000 rpm 1.9v and 2.3V @ 4200 RPM.

I had seen another thread suggesting should be nearer 1.3 at idle, but that was a different class, and info on other cars says < 1 is normal for many. Anybody got the correct figures please?
Thanks
Rob.
 
I could be wrong, but I don't think it matters at idle; the ECU should be in closed-loop operation (i.e. running off the lambda sensor) with the throttle closed.
 
Thanks for the reply. Anybody got a manual that describes the test procedure for this specific model ?
 
Hi its a M271 :-(

I did a not particularly scientific test that I think means it is working ok, but would still like confirmation if possible . (Plugged new one in and pressed it against the old one still in place (instead of the air filter) and they read much the same, certainly at 3000 RPM they were identical, perhaps slightly higher at idle. Didn't want to install the new one until I knew I had a problem as I can still return it.
Assuming the settings look ok anybody got any ideas...

Its a W203 M271, had a O2 lambda sensor upstream warning so replaced it and light is now off. Went for an mot and emissions were 10 * too high. I suspect it has been running rich for a long time and the o2 sensor got sooted up and went rather than being the root cause. Local indie has had it, and can't see anything wrong. It has new plugs, they have checked for leaks(including the 1 under the air box as well at the new upstream lamda.
Any suggestions welcome - if it keep going, may have to write it off, which seems mad given it is a nice car and had from new. (2008 80K)
Cheer
 
Fuel pressure problem?
Damaged injector?
Throttle position sensor?

Have you had a look at the plugs; even if it's just to see if one cylinder is different from the others?
 
A common issue with the M271 engine is split vacuum hose under the air filter housing. The typical symptoms are EML on, rough idle, and poor mpg.
 
....said that, a split vacuum hose will see more air drawn in hence lean mixture, not rich.
 
Hi thanks to all those that posted.

I changed the plugs , but they all looked the same.

The indie knew about the pipe under the airbox, said they checked it , and it had previously had one fitted in its younger days (only other time the light has been on since new)

MOT bloke (who also plugged it in), said his guess was injector so interesting that somebody else mentions that.


Going to try a different garage tomorrow ...
 
Does your M271 run a MAF [ MASS AIRFLOW SENSOR] or a MAP [ MANIFOLD ABSOLUTE PRESSURE SENSOR] they do the same thing but in different ways. If the MAP is reading WRONG all the time signifying a false higher engine load it will cause the engine injection system to overfuel?
Manifold Absolute Pressure MAP Sensors
 
Hi,
I believe (it it is a MAF, and was the last thing the indie wanted to try. I said I would get one in (it was late Friday) and he would fit it tomorrow. However, the one I bought I temporarily placed in the airbox in front of the fitted one (trying to form a reasonable seal) and plugged it in and checked the voltage. They read pretty much identically from what I could see.
:-(
Cheers,
Rob.
 
I'd read about the cam sensor problem, so was one of the first things I checked. There was a slight film on the cam sensor plugs,but don't think it has gone anywhere else. The wires come out of the bottom and then there is a loop in the wires before they go up hill, so can't see the oil could travel. I took the ECU plugs out and they are completely dry and have the old upstream lambda sensor and the plug is also dry.
It really perplexing.
 
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