I recently bought a 93 Escort Cossie, running stage 2 MSD Chip, 360 actuator, greens.

The car has been going fine til it gets to 5000 rpm then runs lean.

Had it on a rolling road and once it gets to 269 bhp it goes back down again like a up and down graph so to speak.

First step was to change the Fuel pump, its not a uprated pump in the car as of tonight.

When i fire it in third once it gets to 5000 rpm it holds back as if its going to stop.

If i dont run it with as much boost and take it slowly it is fine.

What is the problem?

Could it be that the car isnt getting enough air? the car has a aftermarket filter etc on.

Could it be the fuel pressure regulator?

All advice welcome please as it is doing my head in.

The car is supposed to be running 350 bhp, as quoted from Motorsport Developments, so what is holding it back?