AnthonyJ

Guys,

My 98WRX with a Possum has been running like an absolute dream until very recently when I have noticed that the power on hard acceleration is off, especially at higher speeds (50-70 in fifth is massively slower). It is still quick in the first two gears and pulls cleanly but you can just tell it isn't quite running properly - it doesn't quite have the pull. In addition, the A/F meter seems to show that the car is running lean under load (although I must confess that this happened before I noticed the drop off in power).

I'm supremely confident that the car is mapped correctly, because it was done by Bob over a year ago and I have not had any problem with it at all despite regularly giving it a workout (although it has never been on a track). It also still starts and idles fine but just doesn't drive as "urgently" as before.

Any thoughts or suggestions? Presumably either the car is running lean (although I thought that tended to improve performance?) or one or more of the sensors are knackered? Or could it be a fueling issue (fuel pump, blocked injectors etc)?

As an aside, the only other thing that has changed recently has been the fuel - I had to fill up with Shell Optimax (their new s/unleaded replacement), but I did use an octane booster as well just to be on the safe side. Could such a noticeable power fluctuation be related simply to the fuel that the car is being run on? The petrol certainly wasn't the cause of the drop in metered A/F ratio because that had already occured before I filled up. The only thing that has happened subsequently has been the car dropping in power output. It has left me wondering whether the previous tank (Esso s/unleaded) masked the effects better...

Am I slowly driving my car to death? I've eased off for the time being, but I am at a loss as to what to do next. As always, any advice would be much appreciated!

Thanks all!