For the first two years of owning my Rover SD1 Efi Twin Plenum Vitesse, I experienced an intermittent corrupted "Instant mpg" fuel consumption reading on the trip computer. Basically, the normal readings intermittently showed a much lower figure than was either possible or likely.
For example, at a steady cruising speed of about 55 mph in fifth gear, the "Instant mpg" would intermittently never show more than 28 mpg and never more than 45 mpg on engine over-run.
For months I presumed there was an intermittent fault within the fuel management system, testing everything conceivable but with no resolution. Even after replacing the ECU for a different reason the intermittent fault remained, so I turned my attention to the trip computer readout system itself.
This essay explains the cause of the problem and how to fix it.
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Corrupted Fuel Consumption Reading on Rover SD1 Efi Cars
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