Author Topic: Bad mpg, running rich?  (Read 2694 times)

Offline pullafacial

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Bad mpg, running rich?
« on: 30 October 2013, 09:38 »
Hi, I've recently purchased a mk2 gti 16v. The mfa is reading an average figure of around 33mpg which is what is expect. However, when i worked out what's it actually using, it's coming out at around 24mpg. From what I've read the mfa seems to be fairly accurate so what could cause this difference? My guy feeling is that it's running rich as it's lumpy on idle and smells I fuel a bit but would the mfa not take this in to consideration?

Any help would be greatly appreciated.

Thanks

Offline weazgti

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Re: Bad mpg, running rich?
« Reply #1 on: 30 October 2013, 09:55 »
Where did you read that the mfa is accurate  :grin:

Offline pullafacial

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Re: Bad mpg, running rich?
« Reply #2 on: 30 October 2013, 11:50 »
Read it somewhere online. Someone had done an mpg review and found his mfa to be accurate to less than 1%.
I guess what I'm getting at is could a rich running engine cause such a low return or should I be looking for something else?

Thanks again

Offline dragonfly

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Re: Bad mpg, running rich?
« Reply #3 on: 30 October 2013, 14:21 »
Have you checked for fuel leaks?

Offline pullafacial

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Re: Bad mpg, running rich?
« Reply #4 on: 30 October 2013, 15:40 »
Hi, looks like there is a fuel leak coming from above the fuel pump assembly. Drips about once every 10 seconds when running but still smells even when not been used for hours.

Offline oakgreener

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Re: Bad mpg, running rich?
« Reply #5 on: 30 October 2013, 16:44 »
The MFA works on reading the vacuum in the intake. As long as the engine is set up OK as regards to mixture and timing the MFA will be somewhere handy. Not accurate. If you have fuel leaks it will be out.

Offline Gambit

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Re: Bad mpg, running rich?
« Reply #6 on: 30 October 2013, 17:56 »
set the CO%, if its got a lumpy idle then it needs setup.

Offline pullafacial

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Re: Bad mpg, running rich?
« Reply #7 on: 29 November 2013, 20:07 »
So, fuel leak fixed and still have same problem.

Anyone got any other ideas?

Thanks

Offline Sgt_Lemon

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Re: Bad mpg, running rich?
« Reply #8 on: 29 November 2013, 21:14 »
Get it running smooth, timed correctly, mix done. No fuel or vac leaks. A good spark, even compression.

Offline JC

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Re: Bad mpg, running rich?
« Reply #9 on: 30 November 2013, 22:49 »
every MFA will have a different % of accurancy.

They are getting old, as is the associated pipework.

only way of doing a proper MPG is to brim it, drive it, brim it, record figures, repeat.

THEN you can work out your mpg  ( even then your speedo could be over or under reading so could still be miles out )


its a mk2, fill it and drive it and enjoy   :smiley: