Whats happened to my MPG

Last month or two my mpg has dropped from about 12.8 down to average of 9.5. Quite a significant drop... Its very hilly where I live hence low mpg.

Even on motorway its dropped from 20 down to 16.

What can cause this?

In last 6 months I've had new crank sensor, plugs, leads, maf sensor...

No misfiring according to faultmate..

Where do I start looking?

Cheers,
Steve

Steve Ashworth said:

Last month or two my mpg has dropped from about 12.8 down to average of 9.5. Quite a significant drop... Its very hilly where I live hence low mpg.

Even on motorway its dropped from 20 down to 16.

What can cause this?

In last 6 months I've had new crank sensor, plugs, leads, maf sensor...

No misfiring according to faultmate..

Where do I start looking?

Cheers,
Steve

Click to expand...

Air filter. Take it out for a couple of days and see if mileage goes up.

o2 sensors? did you reset ecu long term trims after the new MAF etc?

Will try it and see, although it also had a new air filter in December..

Cheers.

After I changed MAF, plugs n leads I reset adaptive values if thats what you mean?

What readings should I get from O2 sensors..

Cheers

Steve Ashworth said:

Will try it and see, although it also had a new air filter in December..

Cheers.

Click to expand...

Then it seems like a match to me. New air filter in December mpg drops for last couple of months. Lets see December, January how many months is that?

cold months

wammers said:

Then it seems like a match to me. New air filter in December mpg drops for last couple of months. Lets see December, January how many months is that?

Click to expand...

mmmm dont know why that should be but...worth a try

3.5 efi said:

cold months

Click to expand...

Its not that cold now (10deg C) but only got 9.6 mpg today...

Make sure air filter seated properly, if it's an aftermarket jobby fooook it off and get OEM - more to buy but wont drop your economy/power!

tried it without air filter as suggested but no difference?

thermostat??
water temp sensor??

Temperature gauge doesn't deviate from normal once warmed up (a few minutes)?

Have you changed where you buy your fuel? I noticed my MPG dropped when I used Jet compared to BP or Shell.

no - I buy mainly from same place, although it is Jet.
WOuldnt expect 25% less

Steve Ashworth said:

no - I buy mainly from same place, although it is Jet.
WOuldnt expect 25% less

Click to expand...

Nothing scientific but I reckon my MPG was dropping by about 10-15% with Jet. 25% is big time bad.

Does anyone understand the O2 readings that show on diagnostics.

Live data sample attached...

cheers

I'm really sorry and i know i will get all sorts of greif about saying this but....it';s JET FUEL!!!

i have done extensive trials with filling from different garages and the worsed is jet! i get 12mpg from jet and 22from shell sorry, i know everyone will say there is no difference but try it for yourself. go fill up at shell and see if your MPG returns...i'll bet it does!

In that case my next fill will be BP, its just that I pass the Jet station.

PS it wont take long to need a refill!!!!!!!!

Got a very good chance; Jet, just like super-markets, spot-buy fuel that is very near use/sell by date, hence keeping prices lower than BP, Shell etc. Furthermore, their own refined fuel is only filtrated 2 -3 times, as opposed to Shell (5x) Bp (4x). This makes the petrol "cleaner", removing particulates that "dirty" the fuel and lessen it's efficiency.

Shop around, try different local fuel-stops, all vehicles run better/faster/more eonomical on different fuels. Personally, I run all my bikes on Tesco Momentum (higher Ron and more mpg), the Range is better on BP fuel, but lower mpg on morrisons or tesco standard unleaded!