My 98MY Turbo appears to be running slightly rich. It had a service about a month ago (15k), but this doesn't appear to have made much difference. Can anyone else tell me if they have found the same problem, and how I can rectify it. I normally run the car on SUL and do a mixture of short and long journeys.

Thanks,

Andrew

Andrew,

How do you know that the car is running rich i.e. what symptoms are you experiencing?.

The only way to tell for sure is to use a CO2 probe a la MOT test to check the composition of the exhaust gasses. From what I have read, all Imprezas over-fuel to an extent to take advantage of the charge cooling effect of the fuel mist, and up to 10-12% CO2 is fairly normal - high for most cars.

If the car is running too rich (even for an Impreza), then I don't think that there would be much you could do about it, as the fueling is metered by a closed loop control system in the ECU. The ECU uses the lambda sensor in the exhaust system to adjust the pulse width to the fuel injectors, taking into account road speed, load, temperature, and a zillion other factors. I suspect it would re-adjust if you somehow managed to change something to lean the mixture.

This is controlled by the mapping of the ECU, which is where people like Power Engineering come in. By changing the fuelling map, they can liberate some extra power by leaning out the mixture to move it closer to the optimum ratio for max power.

Hope this helps - I have had to resign myself to terrible fuel consumption around town - a 60litre tank lasts about 150miles!

Cheers,

Alex