Update

[alan_edward 0]

Took the car to G-Werks.

 

The car runs well now, with a defenite increase in power.

 

However, Can the MFA give wrong information?

 

For example:

On the way, I filled her up in shell drove all the way to london, did about 98 miles and filled her up. Only had to put £10.88 which means it gave around 37 mpg.

 

But the MFA was in 23mpg slowly increasing to 25.7 , but thats towards the end of the journey.

 

Cannot figure out why..

 

Anyone had the same problem?

 

Cheers

 

Alan

[bcstudent 0]

The MFA, I believe, calculates fuel economy based on the inlet manifold vacuum, which obviously changes with throttle position. It is really only a gimmick and should only be used as a guide.

[Roger Blassberg 0]

The MFA calculates mpg on the basis of inlet manifold pressure; a low pressure, sometimes called "manifold depression", corresponds to a closed or nearly closed throttle, a higher (close to full atmospheric) pressure when the throttle is open more widely.

 

It does it by means of a small-bore tube attached, at one end to the inlet manifold downstream of the throttle and, at the other, to a diaphragm transducer somewhere behind the dash. This gives a signal on a continuous basis to the processor in the MFA which integrates it over time into mpg figures.

 

If there is a leak in that pipe or its connections, the manifold pressure appears to be more than it actually is and the processor will interpret that as a more open throttle position. So, it thinks that more fuel is being used.

 

Clearly it is a rough-and -ready method, but sudden changes or obvious discrepancy can be caused by a leak in the connection, or by a faulty transducer.

 

By the way, your test over 98 miles was nowhere near long enough to give a representative result; just a strong following wind can distort figures upwards over such a short distance. It would be better to do it over 2 or 3 tankfuls to get a more accurate indication.

 

Hope this helps.

 

Best wishes

 

RB