MY96 flat spot

[Bigpete]

Hi everyone,
I have recently purchased my first impreza and i must admit i love it, it had a full engine rebuild and runs and drives perfectly apart from one tiny thing, when you nail the throttle and get to about 4000 rpm it has a big flat spot but if you ease the throttle on it seems to be fine? I have had the air flow meter cleaned etc but still nothing, the guy i bought it from just had the engine steam cleaned and a few places say chances are could be an 02 sensor?
Your thoughts anyone
Thanks all in advance

[stoooo]

Isn't that where the ECU switches over from closed loop to open loop ? I think this can be overcome with a tune and a reflash, but I don't know how easy that is to do on a '96.

I don't know how much it helps on the turbo cars, but on the NA cars putting a lightweight crank pulley on would help it get past that point with a lot less of a dip.

This dyno chart is for two almost identically prepped cars (one has a bad O2 sensor, which is why the line is lower on the scale). You can see the blip in the curves around the 4000rpm mark. The bad O2 sensor is *not* causing the blip on this chart; the power is down along the whole curve, but still almost exactly follows the path of the fully functioning car.

http://farm1.static.flickr.com/89/279350810_75dfd755d7_o.jpg

Bye for now,
Stuart.

[fluffyarwen]

Hi,

I'm having the same problem at 4000rpm, it feels like the car is not getting the grip down, it ain't good when overtaking :o one minute your flat the next nadda!!!

Only had the car since Friday but noticed that this was causing a problem.