[Griff88]

My Mondeo 2.2 TDCI titanium x has just started experiencing very poor MPG this is very intermittent though and can not replicate.

No faults on dash have appeared but have noticed it idles very poorly when it's having it's funny 5 mins. The mpg at 70mph will drop from about 45-50mpg to 12mpg although doesn't feel like it's misfiring or significant performance loss.

The car has done 130k and I have just recently changed the intercooler pipe. Ran a fuel cleaner and egr cleaner through it.

Has anyone else experienced this sort of fault or have any potential solutions?

No smoke or fuel smell

Previous DPF regens have never dropped it that low on mpg not affected the idling

 

[Rekusu]

I cannot help, but my Mk3 2.0 TDCI has recently dropped from what is normal mpg of around 50 to around 43 at the moment. No error codes but wondering if the injectors are squirting more fuel that is needed into the cylinders?

Although that would surely give some kind of major misfiring.

Like you, no smoke, fuel smell, misfire no performance loss and no error codes (also, no DPF) But my idle has increased from around 750 to around 900 and the other day, while sitting at the lights, the mpg was dropping 0.1 every three or four seconds.

 

[stonekeeper]

Watching the "real time" MPG reading on the dashboard is not a good idea.

Is best checked by mileage driven and full to full when refueling.

Cold weather and winter driving conditions can significantly reduce fuel economy.

 

[Rekusu]

Sorry to have hijacked the thread and I totally agree. But I do know how the reading was and what it is now. Just don't even recall having seen it so low.

Used to be rather anal and kept a written record of the mileage and fuel I put into the car so as to have an accurate record of the mpg. Don't do that now!!!

 

[PURPLE_2L_LX]

When I bought the 2L Diesel MK3 I kept fuel logs. Average over full tanks varied from just 29mpg to
over 60mpg.

Snowy weather winter journeys averaged just 29mpg over a full tank. People said it was broken or a
problem but as soon as I did slightly longer journeys the average shot up to over 45mpg.
Average speed during the winter one was just 12mph with lots of sub 1 mile journeys and many just a
few yards whilst taking the inlaws to the doctors etc.

Do you reset the average mpg and average speed on the dash at every fillup?

I reset mine and pullinf out of the petrol station upto the lights it went upto 12mpg and then sitting at the
lights it was counting seconds.. 11.9mpg then 2 seconds later 11.8 etc etc...

Keep a log from full to full or empty to empty and see the real mpg figure. Mine was way off at first but got
more accurate after I started resetting the dash at every fillup.

 

[Griff88]

Oh I know the real time isn't god's truth however I use it as a guide to it's "funny five minutes" on my commute it will usually sit about 45mpg at 70mph sometimes 55 some times 35 this I consider normal.

However now it will tank to 11mpg and coincide with the lumpy idle when pulled up (was 0.2 g/h) now (0.5 g/h)

When lumpyness stops the mpg returns to normal.

 

[Griff88]

Diagnostic update shows throttle position% fixed at 84.3% and throttle position relative is at 0% could it be throttle position sensor. Or just information not supported be my diagnostic equipment

 

[Griff88]

So update. I finally got the car to play up whilst running my data stream. Really rough idle and idle MPG jumped to 0.6 g/h and averaging 15mpg.

Diagnostic equipment lead me to EGR valve which stayed a static 0% and an error percentage of 80% (considerably different to normal running) throttle position was working fine.

I'm almost certain it's the EGR valve sticking. The only issue is 0% is fully closed. Yet my faults are a fully open symptoms. But too much conincidence is leading me to EGR valve fault.