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MG MGF Technical - mass air flow sensor - no F content!

Hi guys and gals, still without an F, enjoying my bike and enjoying taking my daughter in my temporary replacement car - a boring 5 door eurobox.

I am having a problem with my wife's car - a Fiat Multipla, and as the members of the multipla bbs site are not as technical as you I thought I'd ask here! (At least it shows you that it is not only Fs that suffer such silly niggling faults!).
The multipla diesel suffered from a noticeble power loss, not wanting to rev over about 3500rpm. The multi bbs informed me that it is relatively common and was the mass air flow semsor on the airbox and this could be confirmed by disconnecting it. I pulled the plug off the sensor and the car runs perfectly. All other multi owners who have suffered this seem to have subsequently gone to fiat and had a new sensor fitted at a cost of almost £200 (about 50:50 parts and labour).
My question that they cannot answer is : if the car runs fine with the sensor disconnected then what does a mass air flow sensor do on a diesel and why should I bother to pay £200 for a replacement when all it seems to do is cause problems when it fails?
Anybody here knowledgable about such sensors?
Jason H
Jason H

It works out the flow of air into the engine so that the MEMS can work out the fueling.

If you disconnect it the engine will work in limp-home mode as it's assuming the sensor is faulty. Yours seems to work enough to provide a bad, but plausable, singnal to the MEMS.
Without it the engine will not be running at 100% efficiency which affects performance and economy.

Go to a breakers to get a replacement?

This is all from memory... :)

P.
Paul Nothard

Thanks Paul,
Unfortunately the multipla is not a common car at breakers. Loks like i'll have to buy a new one from the dealers!
Jason H
Jason H

Are there other cars that share the same (or similar enough) engine?
Paul Nothard

I agree with Paul- the ECU will require the airflow signal to calculate ignition and fuelling maps: I am amazed the car runs as well as it does without! Not an ideal state of affairs though...

The airflow sensor is almost certainly shared with another Fiat or Fiat group car - but which, I have no idea :o(
Rob Bell

The car is running fantastically - so good in fact that even my wife noticed the difference and described it as a lot more nippy!
One of the other multi owners has disconnected his sensor and says he detects no difference in performance, we think that with the sensor disconnected the ecu asumes max air flow and fuels accordingly - hence steam ahead - as it is a diesel there is no ignition timing toi worry about. The only flaw to our assumption is that if the ecu was adding fuel to go with max air I would expect a lot of black smoke at partial throttle, but there is none!
Jason H
Jason H

It depends on what it's metering, on the K, the MEMS uses the MAP (manifold air pressure) sensor to work out how much air is getting sucked into the engine, so it uses pretty much only RPM, and pressure to work out the fueling*. To do this the sensor has to be downwind of the throttle plate.

On other ECU's the MAF may be in another place, you say 'in the airfilter' if you mean upwind of the throttle plate then the ECU may just be using the throttle position to work out how much air is flowing, then doing a little adjustment depending on airpressure. If you disconnect the MAF then the ECU will assume a standard pressure, probebly sea level. which will be fine in the UK unless you end up on the side of a mountain.
Will Munns

A lot of fiat's are the same under the bonnet and i would imagine the multipla has the same engine as a marea deisel in fact i would put money on it!!!
Nick

Multijet -- made in Poland with industrial partner General Motors

Notice the difference of multijet system to older Fiat diesel engines with common rail.
Dieter K.

This thread was discussed between 04/08/2004 and 08/08/2004

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