mfa says 75+ mpg ? help

Hi
  My GTI, in the seven years I have owned it has always read a high mpg on the digital display.
      Is there a diode or something somewhere I can change .
    Also since I fitted an oil pressure gauge, and solderd into the wire sending the signal to the mfa , the VDO gauge works fine but the reading went from that mfa position.
         Any help would be great, thanks
                         Ali
 Sorry I just noticed I ment oil temperature gauge.   mon 10.4.06 2015hrs

Mine says a permanent 99.9 MPG, ocasionally dropping below that if I give it a hard time. I think it's just the 70's/80's electronics really isn't very accurate.

As for the oil pressure gauge, I didn't think there was a sensor for this in the mk1 as standard, the read out on the mfa is oil temperature, not pressure as far as I know? I would guess the mfa doesn't like the fact that something else is stealing it's signal, it's probably changed all sorts of characteristics in the wiring, like resistances and voltages, upsetting the electronics in the mfa.  I would probably put in an additional sensor for the vdo gauge, and leave the existing wiring as it is, creates less problems.

Mike.

My MPG is usually approx double the real fig or 99.

The original oil presure senders are simple on/off switchs to run the low presure light and buzzer. As mentioned the MFA is temp not pressure. You need a VDO oil pressure sender that matches your guage.

I don't think there's an electronic component you can change to sort out the MFA reading.

You might want to check and clean the electrical contacts on the distributor and alternator and the cylinder head earthing strap*. Also check the vacuum hose that comes from the intake manifold for leaks/holes.

If that doesn't work, console yourseld with the thought that if the MFA were analogue, it would probably be the size of your gearbox, rather than fitting behind your dashboard….

Ali Cabrio


*MFA fault-causing prime suspect number 1

My MFA MPG has always read too high, over 2 mk2 GTi's and 2 cabrios.  It does change when the CO adjustment is altered though.  I think it is derived from the manifold vacuum, and a higher vacuum means that your foot is not so close to the boards.  The MFA vacuum line should not be fitted after any one-way valves.  Otherwise, I think its the block on the back of the dashboard that decides how much fuel you're using.  

Big

It is only an estimation, becuase all the fuel injection system is manual on a mk1 (early ones anyway, later cabs had electonic injection i believe) there is no way of the electronics knowing how much fuel and air is coming into the engine, so there is no way it can really know what your MPG is.

MFA on golfs was only a gimmic in my opinion, and doesn't really serve a useful purpose. The temperature readouts are just as bad, if you switch to the oil temperature, then turn on your fan blower and head lights, the reading jumps about 8 degrees straight away becasue of the changes in voltage in the car, so that's not very accurate either.

Mike.

Many thanks for your comments and help
                    Ali

dont knock it,petrol is 94p per liter  
Bert

a few years ago i had a mk2 gti, wifey wrote it off but ever since i've had rose tinted memories of that car. especially the MPG that i thought it returned. it never occured to me to actually work it out. now you've shattered all my illusions.  

do ya feel guilty now?