tobler

Hi

I think im having an issue with my MAP sensor on my cls55 engine.
Its giving out a constant reading of -38 hPa no matter how much I rev it.
I even replaced it with a new one, still no proper readings

No faults stored in ECU

Anyone encountered something like this before?

hayseed

iTrader: (2)

not sure, what other issues are you experiencing ? has the car had a tune or pullys added to it ? that thing is not easy to get to for replacement is it ?

tobler

The car is all stock. no tunes no pullys.

other problems:

-The intercooler pump needs to be replaced as the intake temp is too high and im experiencing SC shutdowns.

-I reckon the sparkplugs need replacing aswell since the engine vibrates a bit at 900-1700rpm when cold (in D and P) and It prolly never been done ( 86k on the clock ).

I think my car doesnt pull as well as it should ( though I havent tried any other 55's). I guess I put it on a bad Intercooler pump and sparkplugs for now.

And I cant think of any reason why these 2 problems would be related to my bad MAP readings.

Oh and yea sensor was a hell of a *unt to replace

Dublinoh

Can't help with main problem, but engine and/or trans mounts should be checked too.

tobler

I will check but I doubt thats the cause.
The problem goes away as the engine warms up.

Hotsauce55

I think MAP readings are directly related to vacuum. Are you certain you don't have a vacuum leak? Could explain rough idle too.

tobler

thanks for the info, gonna look into it on the weekend and report back

E55wannabe

What does the sensor read unplugged?

tobler

haha, good question. its not that easy to test.
BUT .. I had it unplugged (by accident) for a few days.
It gave me a CEL and it felt as if the fuel mixture was running rich.
And a fault code was stored in the ECU. After that I replaced the sensor with a new one and deleted the fault codes.
And the new sensor worked just like the old one: not getting any correct readings

E55wannabe

The reason I ask is if you have a wire pinched or chafed and shorted to ground it could be giving you the oddball errors.

Try turning the ignition on and monitoring the sensor reading without the engine running, it should show you atmospheric pressure.

tobler

I could not test with a diagnostics tool right now but I did test my old MAP sensor ( the one I replaced with a new one ) manually with a voltmeter and mouth-vacuum
I definately saw the sensor working as the voltmeter was reacting to different levels of vacuum.
So my next step will be to test the wiring of the map sensor, especially the middle pin wire of the MAP sensor, as it is the one to send signals to ECU.

fingers crossed for the wire to be broken / pinched .. otherwise im running out of ideas

E55wannabe

If it's like every other sensor that I have seen, it's three pin. You should have +5v, ground and signal to the ECU. best of luck.

tobler

a little update on the matter.

the signal cable of the MAP sensor is alright. Tested with a voltmeter from both ends ( MAP sensor plug & ECU plug ).
So next thing I'll do is trying to measure the signal from the ECU plug with a voltmeter with running engine and boost. who knows, maybe my diagnostics tool is acting up (no readins) and Im chasing after ghosts