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Speedometer swap, where is the mileage stored?

MisterCorn

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Joined
8 Jan 2011
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9,410
I am doing work on the speedometer for my 996 project car. The car is in pieces and will be for ages, so I want to test my electronics by fitting the C4 instruments to my C2. My C2 is on 61k miles, the C4 on 192k.

Am I right in thinking that the mileage is stored independantly in the ECU and Instruments, so if I swap them then any miles clocked up will show as a difference when swapped back? I don't mind that so much as distances will be negligible. What I don't want is for my C2 to think it is on 192k when I swap the instruments back. TBH I don't see how it can with knowing the connections between the ECU and Instruments, but thought it best to see if anybody else has insights from previous instrument swaps.

MC
 
The ECU only shows total hours run so it'll just add more time to the clock.

I'm unsure if the ECU will see the clock swap and throw a paddy though but you may have to calibrate the fuel sender/gauge as the two tanks are different?
 
Not so fussed about fuel tank. I'll do a few miles. It is a simple voltage from tank to instuments.

MC
 
Miles/km is stored on the instrument, only hours run and average speed is stored on the ecu. Simple calculation to ascertain if a car has been clocked I used when viewing cars to buy when I hooked up durametric for over revs and faults etc
 

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