So really, an adjustable FPR "should" only help at WOT performance. So my s**t fuel economy is most likely to be occuring due to dodgy O2 sensor or MAP sensor then? I ran the self diagnostics on my car and MAP seemed to come up ok, does anyone then know how to check the O2 sensor for correct operation?

If the ego is the eyes of the ecu to adjust fuel then why not get an adjustable fuel pressure regulator and disconnect the ego.Sure the car will go to rich but that can be adjusted with the pressure regulator...cant it?

I saw a Malpassi adjustable regulator on ebay a while ago that had no guage on it but looked very much to have the right shape and bracket to be a straight bolt on to the EF fuel rail exactly as per the factory reg - ie. it had an O ringed spiggot out the side and a bracket that had 2 holes in line with and either side of that spiggot - and there was a hose fitting sticking out the bottom. Overall exactly same configuration as OEM reg.

UPDATE: I've just saved a picture to the gallery - it's off ebay for some kit for Subaru - the significant thing is the regulator ON THE FRONT OF THE BOX - look close and you'll see that regulator would indeed be a straight bolt on for EF - it's the one I described above and has an O ring spiggot and the bracket to take 2 bolts the way EF OEM reg is fitted. I have searched and searched and haven't found the actual regulator itself yet.

Lowering or raising the fuel pressure will affect the injector spray patterns. Also it's pretty crude especially if you arn't doing it with a wide band O2 sensor. A bit like turning the dizzy for spark advance/retard. Your full load/wide open throttle might be ok but your idle and low load might be stuffed. And you won't even know untill your engine blows up!

If you don't have enough money for a proper form of engine tuning then you not going to buy a wide band O2.

Because then you loose all the adaptive control the EEC has built in. The HEGO is used to check that the targeted AFR is actually the AF ratio the engine is running at. Also I am sure running without a HEGO will cause a fault code and probably lead to a rich/safe mix.

But as said, AFR will only effect WOT and even there the EEC will learn around a propartion of it. It is only really used as a cheap dodgy way of controlling AF ratios.

Well I think you have summed it up for me there Grant. I was just looking for cheap, and unfortunatlely its dodgy too and I dont want to go down that path. Thanks for all the replies people