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High fuel consumption Z3 2.8

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325iRon View Drop Down
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    Posted: 30 Jul 2018 at 8:41pm
I have had my Z3 for 12 years and it's always been very good on fuel. 32+ on a run and 20 + in town. Last weekend and this weekend two m/waytrips at a steady 60/70 mph  only 28 mpg. A run into town today 7mpg !!!!. Any ideas would much appreciated. Oh milage is 98000.
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Mike Fishwick View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike Fishwick Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jul 2018 at 9:08am
Hi Ron - hope all is well in WSM!

There is certainly something wrong - I have just returned home after a 2000 mile trip around the UK, and averaged 35 mpg on an MFA which I have calibrated to be within ± 1 mpg.

The MFA may be faulty, or it is not receiving the distance signal from the speedometer.  I have had this kind of MFA readout, in conjunction with a loss of speedometer reading, due to the connector on the final drive having fallen off.

Have you checked the fuel consumption over a tank full to tank full period, and calculated the true consumption?   At 7 mpg I would expect the exhaust to smell of fuel, even with a catalytic converter.

What do the spark plugs and the tailpipes look like? 

Your problem could be as basic as a fuel leak - I recently found a small leak from the rubber coupling on the inlet side of the fuel filter.  After 20 years it had become softer, and was no longer sealing properly, and needed a little tightening.  There was no smell of petrol in the garage, and fuel consumption did not seem to have been affected, but a larger leak which had been dripping for a considerable time could increase consumption quite a bit.

Other causes could be binding brakes (calipers or handbrake shoes) or possibly a choked catalytic converter.  This can be checked by a differential pressure test, although it is not common.

Unplug the airflow sensor and see what happens as an airleak in the intake bellows will cause weak mixture, requiring more fuel to keep the mixture strength up.  A faulty coolant temperature sensor is another possibility - try unplugging it when the engine is hot.  Have the fault codes read and reset afterwards.

You just have to check everything, as on a carburetter engine.


Edited by Mike Fishwick - 31 Jul 2018 at 4:10pm
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325iRon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 325iRon Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jul 2018 at 11:32pm
Hi Mike thanks very much for the very coprecomprehe answer. I knuckle down in the morning, and hopefully sort it out. 
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