I've noticed on my MY00 impreza that in 4th gear at around 4000rpm the car seems to stop pulling as hard and then picks up again at around 4500rpm. The car has done 45K and only has a ful de-cat system at the moment. Its had the 45K service at 42K.

I guess this is whats known as a flat spot?

The car doesn't do anything else out of the ordinary. It is a bit hesitant for the first couple of minutes when cold but I guess thats just the lambda warming up.

Plan to buy new O2 and MAF sensors soon as a precuation just in case these are on the way out.

 

hello mate , i've put a post on here asking (flat spot in my MY01) the same question, I've run the car on optimax. IU've just taken the car out again and given it a blast. Pulls to 4.2K then stalls, then when it reaches 5k it goes like a rocket. Have you just put an exhaust on or have you had it rempped?.

Seems nobody has had this problem except us...come on some mappers "please" must have seen this flat spot problem before.

 

i have this problem on my96 wrx after recently fitting a decat system[resetting the ecu helps abit ...its anoyong as i havent had the gains i was expecting from the decat.

 

i don't know if you can reset a bugeyes ECU? if anybody does please post

 

I always thought the true gains would come from decat and remap at the same time. The remap sorts out the flat spots as far as I can tell.
Daz.

 

Had the same problem!! had a full de-cat and K&N fitted, complete lack of power at around 4000 RPM picked up again after 5000RPM.

Popped the car up to bob rawle from B&R dev one evening, turned out on mine that the decat was making it run very lean around 4000RPM, the turbo was also very lively running 1.3Bar!! this meant loads of boast and no fuel!! bob reduced the boast back to 1.0bar with a restricter as a fix until I can get it booked in for a remap, when the fueling can be looked at.

Had no problems since,

hope this helps
Dan