I fitted a Scott Tayor chip to my 93 wrx ra at the weekend. Car started fine with no warning lights coming on.
I cannot really tell if it feels any quicker but it now hesitates at around 4500 rpm, it was fine before with very smooth power delivery. I changed the pump for a walbro 255 but that made no difference(i thought it was leaning out at high revs)
Any idea's i know there is not much to go on.

 

The increase in boost pressure (chip associated) may have highlighted a problem with your coil-packs - meaning they could be 'breaking down'
Remove the coilpacks and check under the rubber shroud which goes over the plug - if there are any cracks in the ceramic then they are likely to be the problem


Cheers

 

Cheers mate have a look when new plugs go in next week

 

Agreed...Raise in boost pressure will put coils and plugs under more strain.You will find your problem in this area,Scott T's chips are excellent and trouble free.