thats odd bc out of the 100+ cars i have installed walbros i have never run into that issue.


and nora, sure you can up your fuel pressure to get more fuel... but at the expense of your injectors over driving and dying. why do you suppose the FMU went out of style like heroin and david lee roth?

the proper way to adjust fuel is through duty cycle. forcing more fuel through is not good. as far as vacuum, the reason for it is that under negative load (vacuum) the fuel pressure is lower. under WOT, the fuel pressure raises. additionally, under boost, the fuel pressure rises 1psi per lb of boost. FMU's totally negate this and burn up injectors.

for example:

45 psi fuel pressure static (no vacuum/no boost)

on factory regulator:

45psi + 15psi boost = 60psi of fuel pressure... cool, no biggie

on just an 8:1 FMU (considered low ratio):

45psi + 15psi boost = 165psi of fuel pressure [45 + (15x8 )]

and there are FMU's that go as high as 14:1!! scary stuff!! this is how turbo kits used to come in the late 90's with an additional fuel pump inline. no ecu controls, no tuning... just rediculous fuel pressure.

but back to original, the jump from 38psi to 45psi at idle will richen the setup, but not to the point that you would have some crazy rich condition. especially if your pressure is beind raised via a vacuum leak. in fact, the vac leak will cause more of a lean condition than the 7psi increase in fuel pressure will cause a rich condition.. if that makes any sense.