A friend of mine was settin me car up today after it bein off the road for more mods, and couldn't get it to fuel properly over 1.2bar boost (wantin to run 1.5), still on mfi. It would fuel ok up to about 4k on 1.5bar but then steadily lean out from there till it was goin towards 1.0 lambda. This was happenin even with increases in fuel pressure, whereby it would become rich as hell at the bottom of the rev range makin it horrible to drive, but still not givin any more fuel at the top of the rev range. The fuellin was bein monitored via lambda probe in the front pipe and a motech monitor in the car (so proper monitoring), all we can think of is that the meterin unit is faulty or the fuel pump not supllyin enough fuel???? The fuel pump's a brand new bosch jobbie, with the supply bein re-wired so no problem with low voltage. Any ideas lads

 

MFI is classic for this mate, injection with the drawbacks of a carbeurettor. How did you increase the fuel pressure???? Have you replaced the regulator for an adjutable one?

Two mods which are done to help with high end fuelling, are putting a vacuum hose to the standard pressure regulator (?? not too sure if thats an option for you if you have changed it), and theres a screw on the back of the hydro electric pressure actuator which can be adjusted (the hydro electric pressure actuator being the sole component that controls enrichment of the mixture). I dont know the exact procedure and i wouldn't recommend having a play with it blind so to speak.

Also, check your Throttle Position Switch is fully working, if that breaks the car will never give full enrichment on boost (the switch being the sole component that triggers full enrichment)