Whats happened to my MPG

Steve Ashworth · Feb 4, 2011

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

wammers · Feb 4, 2011

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

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

rasheed · Feb 4, 2011

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

Steve Ashworth · Feb 4, 2011

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

Cheers.

Steve Ashworth · Feb 4, 2011

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

wammers · Feb 4, 2011

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

Cheers.

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?

3.5 efi · Feb 4, 2011

cold months

Steve Ashworth · Feb 4, 2011

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?

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

Steve Ashworth · Feb 4, 2011

3.5 efi said:
cold months

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

Ridesafe · Feb 5, 2011

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!

Steve Ashworth · Feb 5, 2011

tried it without air filter as suggested but no difference?

juiceyv8 · Feb 5, 2011

thermostat??
water temp sensor??

Steve Ashworth · Feb 5, 2011

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

jt_armstrong · Feb 5, 2011

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

Steve Ashworth · Feb 5, 2011

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

jt_armstrong · Feb 5, 2011

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

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

Steve Ashworth · Feb 5, 2011

Does anyone understand the O2 readings that show on diagnostics.

Live data sample attached...

cheers

ladyranger · Feb 5, 2011

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!

Steve Ashworth · Feb 5, 2011

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!!!!!!!!

Ridesafe · Feb 5, 2011

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!

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