MFA fuel consumpion figures.... lies!

[Jimbob1970 0]

On my 'new' VR6, the MFA fuel consumption figures are around 31-33 mpg most of the time on trips, and on the second setting the 'long term' figure is also over 30 mpg.

 

But, I know that I just about managed 370 miles out of a full tank (15 gallons).

So that means 24.6 mpg

 

Is anyone else getting "optomistic" readings from their MFA?

 

Jim

[davidwort 0]

On my 'new' VR6, the MFA fuel consumption figures are around 31-33 mpg most of the time on trips, and on the second setting the 'long term' figure is also over 30 mpg.

 

But, I know that I just about managed 370 miles out of a full tank (15 gallons).

So that means 24.6 mpg

 

Is anyone else getting "optomistic" readings from their MFA?

 

Jim

 

The MFA is quite simple in that it's not measuring your fuel usage at all, only inlet manifold pressure and road speed, there's plenty of margin for error, even tyre tread depth on the correct wheels and tyres for the model will affect it, I've found they all over estimate, my mk 4 golf is the same. Best used as a guide only. My 16v is usually about 2-3 mpg higher than actual tank to tank, they seem to get more optimistic in the winter - not exactly sure why? - perhaps down to more rich running in the cold start-ups. You could have a slight leak on the vacuum pipe/sensor to the speedo too.

 

David.

[Jimbob1970 0]

Cheers David.

 

I won't trust the b*gger any more!

 

It was pretty accurate on my 16v though.

[dr_mat 0]

The VR's MFA miles-per-gallon readout is driven by the ECU, so it actually KNOWS roughly how much fuel it's putting in, and how far the car is going, so it should be pretty accurate.

I doubt you used ALL 15 gallons or did you, in fact, fill the car to the brim, then drive until it ran out of fuel?

At the MFA's projected 31mpg you would have had 3.1 gallons left in the tank when you filled up, which is probably quite feasible knowing how flaky the fuel gauge reading is - how many litres did you put in?

[Jimbob1970 0]

Dr Mat,

 

I filled it to the brim, and drove until it started spluttering out of fuel.

I only just made it to the petrol station! - and that was not deliberate...

 

When I re-filled it to the brim again, it took just over 55 litres - so it must have had nothing left in there....!

[dr_mat 0]

55 litres is 12.34 gallons == 29.97 mpg.

There were 2.7 gallons left in the system somewhere...

Not a good idea to run a car down till it's spluttering due to lack of fuel, on the whole....

[Rpmayne 0]

:shock: After reading this thread I've just checked my calculated MPG. 64litres does 280miles normally. That works out at 19.4mpg (280/(64/4.5)). The VR's MFA normally reads around 25-27mpg. Definitely some inaccuracies somewhere, and on standard wheel/tyre sizes.

[dr_mat 0]

Rpmayne, did you actually put 64 litres in the car? I rarely get more than 55 litres in mine. My MFA is usually pretty accurate. And it looks like jimbob's is too...

[Kevin Bacon 5]

Not a good idea to run a car down till it's spluttering due to lack of fuel, on the whole....

 

Quite.... the nice new fuel filter I put on last year was clogged with lovely black sediment through doing that.

 

I'd personally up the fuel filter service to 12,000 miles/annual instead of the prescribed 24,000/bi-annual.

 

Jimbob, your car should have a 70 litre tank mate.

 

I've done many calculations of MPG on mine using the old fashioned method and the MFA and found the MFA to be 2% optimistic. My engine has averaged 28mpg over the last 3845 miles (MFA 2). Not bad considering how I drive it and it's shricked, cam'd and chipped.

[Jim 1]

Unfortunately my car flat out lies on the MFA about the kind of fuel economy I get.. but there are all kinds of interesting behaviours, etc too.

 

Because a lot of my driving is just too and from work and to mates houses (which are no more than 20 minute drives in traffic) I basically get terrible economy.. but the MFA quite merrily assures me I am getting anywhere from 25-30MPG. Working it out myself, I know I am getting nearer 20MPG.

 

I was worried about the health of my car (about 240 miles from a full, later style tank) but as soon as I take the car on a long, dawdling drive the economy is hugely better - I drove to Blenheim Palace last weekend and got about 170 miles and the needle was still well over the half way point on the fuel gauge.. it was only when I came back to Cov and resumed my usual morning slog type driving that things went Pete Tong again. So no problems there, just the classic case of the G60 being terrible for traffic and short journeys!

 

Different types of fuel seem to affect the MFA too though.. I used some Esso unleaded a while back (ALWAYS use BP Ultimate) and the MFA was actually being accurate most of the time - failing to get above 22MPG, etc in traffic and basically telling me the horrible truth. Wonder why Ultimate makes the car lie...

[dr_mat 0]

MFA on the G60 operates on the inlet manifold vaccum as described above, so yes, it's going to be a little/a lot inaccurate.

The VR6 does it the *right* way - i.e. eithin the ECU, so there's not really a lot of excuse for the VR to be wrong.

[Jim 1]

MFA on the G60 operates on the inlet manifold vaccum as described above, so yes, it's going to be a little/a lot inaccurate.

 

Indeed.. I was told that its also preprogrammed with certain values, so MFA figures should basically be ignored on modified G60's..

[Geo 0]

My MFA on the golf is generally about 10-15% too optimistic on the mpg figures it gives. It normally reckons around 33-35 as an average while the actual average is around 30ish.

[mark28G60 0]

My MFA reads about 3 to 4mpg better than im actually doing.

I drive for 1 hour to work in some traffic (35mins) some nice and clear 70mph roads so its fairly average.

Mine reads 30mpg where actually i know im getting 27mpg or so.

 

290miles/49ltrsx4.55(ltrs to gal) = 27mpg

I think thats right?????

 

Mark

[paddyg 0]

I usually reset my mfa miles travelled setting and also reset the analogue clock in the dash (its an early valver) and they mfa is always out by a mile or two!!!

[mistrall 0]

my mfa says i doo from 2mpg to 15mpg - defo not right lol

[Jimbob1970 0]

Kev,

 

Cheers for the advice.

I have got it booked in for new filters/oil/plugs and a service next Tuesday, even though it isn't due a service for another 5k yet.

I will discuss the timing chain/guides/tensioners/clutch job with him then.

Also, I am finding the brakes rubbish, so I will see what he can do about that too....

 

 

:roll:

[Kevin Bacon 5]

No probs, make sure they use genuine parts only, especially where the plugs and filters are concerned!

 

Brakes....hmmm, not really much you can do with those without upgrading calipers and discs etc. The ABS pump on the VR makes for a very mushy pedal unfortunately, so upping the strength of the calipers etc can help get round that.

The 288 setup off the Golf highline is a cheap and effective mod, otherwise it'll be Brembos and the like for you sir!

 

Braided lines all round and MK4 rear calipers I've found removes a lot of slop from the pedal feel though.

[Jimbob1970 0]

Cheers Kev.

 

I will look at the price of the 288 setup off the Highline then, I will talk to the bloke about that next Tuesday.

 

How much can you get for a kidney on the black market.... we only need one don't we?!...

[Dec 1]

my mfa says i doo from 2mpg to 15mpg - defo not right lol

 

I get 10-15mpg according to mine!!! :shock: ....scared the crap out of me the first time I saw that after buying the car, thought I'd have to invest in Esso!!!! :)

[Danr 0]

mine once claimed i was gettin 99.9mpg :D although the way the petrol gauge was goin down i knew one of was lying to me :mad:

[gradeAfailure 0]

I think the general concensus is that if you're getting 99.9mpg then one of the vacuum pipes is blocked; and my own experience is that if you're seeing about 10-15mpg (and you know it's better than that!) then one of the vacuum pipes has come off the little swirl-chamber-thingy (technical term, obviously ;)) in the engine bay - mine had actually snapped off...

[Dec 1]

ahhh yes...the "swirl-chamber-thingy" I know it well :lol: