Have been noticing a slight hesitation at high revs for a while so decided to change the fuel pump for a walbro 255. On the day I had the pump changed I noticed that the pull mid and high revs was down slighlty, did'nt thing much of it just looking forward to haveing a relyable new pump fitted. (so noticed sight low power before pump is fitted).
New pump in and problem is much worse. so drove home to re-set ECU (properly vire OBD port) so solve problem. Still lack of power after 3000 RPM.
Have done some logging before and after pump and cant see any significant differance in:

Boost around 13.5 to 14.8 PSI
ARF under full power 11.5 (sounds very rich to me not sure)
injector duty cyle 98%

I have just cleaned the MAF sensor (will try on the way to work in the morning) but it looked imaculate.

Anyone have any ideas on what I should/how to check next??

MY04 stock wagon apart from a Prodrive BB, K&N filter and new walbro pump

 

The fuel pump wouldn't be the first thing I'd look to for a hesitation like you mention, have you looked at your ignition system, plugs etc?

Are you using a wideband to measure your AFR, if not that reading isn't accurate. Besides a WRX is a lot richer than that standard.

 

Plugs where changed at 60K mileage now at 87K (stock plugs). Leads are original. Not using a wide band sensor to measure AFR just logging from internal sensors.
Is it possible to check plugs easily?
Thanks for reply.

 

had similar problem with hesitation turned out to be coil packs.

 

Could you surgest somthing cheaper!!!!

Now people mention it ignition system seems to make sence.

 

if your not getting a strong enough spark under load then it wont go.when my fault occured a refused to think this was problem, spent money on other things that didn,t need doing to find out in end was coil packs.jolly green giant do them.

 

Can they exhibit intermittant faliure, as car feels better this morning but still not right.
Is it possible for a garage to test them without the old just replace and see technique we all know and love
Thanks for info bigchap I will look into it.