I have a Walbro 255 and I accidentally had the base fuel pressure set to about 51psi (40psi at idle) and at about 10psi of boost the A/F went a little lean. Will too high fuel pressure cause this lean condition in the higher RPM range? Is 60+ psi fuel pressure out of the pump's efficiency range?

 

did you rewire the fuel pump?

 

Q1: no way as that is a violation of not only common sence but of physics.
Q2: Depends on the pump.

 

Yes, I did Dale Clark's rewire mod.

 

You may have been seeing a rich misfire - if you get it REALLY rich, sometimes it will show as a lean spot. 10 extra pounds of fuel pressure really isn't helping .

What FPR are you running?

Dale

 

Aeromotive A1000-6

 

51 psi should be fine but it is in the range that the pressure could overcome the injectors ability to open causing a lean condition. I believe 60psi is considered the max for static (no vac line) fuel pressure. depending on the condition of your injectors etc. 51 could be causing an injector (s) to not open fully or at all in the full boost ranges.