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!

 

Anthony,

I'd re post this in drive train m8. You'll get more replies there. This is a technical question, so pop it over. Plus I'm interested in the answers to this question too, just out of curiosity.

Cheers,

Wrexy.