MFA average speed wildly over-reading.

[aclwalker 3]

Hi,

 

The other day my MFA started to wildy over-read in the average speed. It was stating about 2-3 times the actual speed. I verified this by resetting it while at a constant speed and the result was the same. Positions 1 and 2 seem to be the same.

 

Then yesterday my clock had reset itself to 00:00 as well. I reckon it must've done this when I started as it was bang on the number of minutes I had been driving for.

 

Any idea what's causing this? It was very accurate right up to the other day. I'm one of these people that likes to use the MFA because it means I get to know the car extremely well as regards MPG, temperatures etc. and can spot problems pretty quickly this way.

 

Incidentally, the oil and ambient temperatures seem totally normal. It's just the average speed, possibly the MFA mileage too (not checked it on long enough a trip yet) and now the clock.

 

Any ideas anyone?

 

Thanks

[Trig 0]

AFAIK The average speed is worked out from using the distance reading and the time reading (S=DxT). Dunno if that helps.

[gradeAfailure 0]

Could be an internal electronics fault in the clocks, as if the speedo's reading correctly then the sender on the gearbox is obviously ok. Best thing is to try another set of clocks - it's only 15mins to swap them over.

[dr_mat 0]

Sounds like the timer chip on the MFA is fubar.. Not sure how integrated into the ECU this is, but it certainly sounds like you've got to swap the clocks over at the very least.

[old man 0]

Had similar problems changed clocks and all runs fine :scatter:

[aclwalker 3]

Hi,

 

I've just done some more 'testing' and the clock is definately the culprit. Each minute is lasting about 3 real minutes. This is definately a new fault in the last week or so as the clock always worked fine (although it did lose a couple of minutes over periods of months before, but nothing to worry about).

 

Did Einstein not say that time slows down if you're going too fast? :wink: Maybe I should slow down.

 

Two other things I've noticed:

 

1 MFA setting 1 is no longer forgetting its settings after the normal 2 hour period.

2 I _think_ the clock is running at normal speed when the ignition is off, but I've yet to verify this over a longer test period.

 

A dodgy connection somewhere perhaps?

 

Also, the odometer, tripmeter and MFA distance reading all appear to be correct. So is the MPG reading, which is no great surprise as there's no time element in that calculation.

 

As for swapping over clocks, what does this involve? Is it just the clock part or do I need to replace all the dials? How much is a new one etc?

[Taggart 0]

AFAIK The average speed is worked out from using the distance reading and the time reading (S=DxT). Dunno if that helps.

 

Or S=D/T :wink:

[gradeAfailure 0]

Easiest thing is to get a clock unit out of a car being broken, and just swap the entire assembly over - what C is yours?

 

To replace clocks, simply undo 4 screws securing clock surround, drop steering wheel down, remove surround, remove two screws securing clocks (one each side), tilt clocks forwards, disconnect speedo/MFA vacuum hose/multiway connector (delete as applicable), remove clocks from car. Refitting is, as they say, the reverse of removal!

 

:)

[aclwalker 3]

Thanks for the replies. Mine is a 1994 VR6.

 

The really strange thing is that I can now confirm that the clock is working perfectly when the ignition is off. Once I start driving the car it slows down to about a third normal speed. Surely this shows that the clock is not faulty but that perhaps there's some voltage issue or something?

 

If I swap over clocks and so on, do I lose my mileage reading on the odometer?