running lean only under high load/high rpms

[a351must2]

I have a '96 Eclipse GS-T auto w/ Injen Intake & Filter, RRE UIC pipe, 1G bypass valve, Gillis boost control (ball/spring) @ 17psi, Walbro 255HP fuel pump, and Autometer A/F and Boost guages.

I used to have a problem with the engine totally cutting out when below half tank and turning left at full throttle. That problem disappeared when I installed the Walbro 255HP fuel pump.

Ever since installing the Walbro pump, I've had a problem at either high speeds or on hills where the A/F ratio shows rich until about 60mph and then it starts dropping quickly to totally lean by 80mph. If I'm on a hill it starts dropping even earlier. If I back off the gas a little, the A/F ratio moves back towards rich.

With the stock T25 turbo, I usually don't see more than 12-14 psi above 4000rpm and I noticed, in situations where the A/F ratio starts dropping, that the boost starts creeping towards the 17psi mark...it's usually gone lean by the time it reaches about 16psi though and I back off of course.


Any ideas on this? I see plenty of people with the same size pump and no problems. The only idea I've had recently is to do the fuel pump re-wire that I haven't done yet. Is the stock fuel pump wiring unable to keep a Walbro 255HP running at full power?

 

[44pirate]

Change your fuel filter lately.

 

[a351must2]

I've got a new fuel filter sitting in the trunk...tried to change it once and couldn't get either line to break loose. Last time I was at the dealership they'd said it was unlikely that the filter was the problem, and I believed them....maybe I should do that.