I will post a fix for this when I find out for future searches
87 GN. All stock except for TT street chip, test pipe, catback, kn filter and comp valve springs.
A couple months ago I installed brand new parts to get ready to turn the car up:
Walbro pump/sock/hose
Casper HW kit
Fuel filter
Accufab FPR with Marshall fluid filled gauge
Car ran the same. Recently I installed more parts:
Fast XFI
120lb precision injectors
GM flex fuel sensor in the return line
car is now on e85
Problem #1
I cant get the fuel pressure below 50psi static. When i put the vacuum line back on it, it quickly dips to about 48psi, then immediately jumps back to 50psi. If I drive the car for a while, the static fuel pressure drops to 45psi (line on or off does not make a difference. The vacuum source is good.
First thought here is a restriction in the return line. But ....
Problem #2
When I blip the throttle, the fuel pressure drops about 10 psi. This is dead opposite of problem #1. I suspect It is not raising under boost either but i cant see the gauge while driving. I suspect this because I had to add a lot of fuel to the VE table under boost to get the AFRs right.
Why would fuel pressure change after the car warms up? I dont believe it is a faulty gauge because I can see the O2 corrections and it correlates to the fuel pressures shown on the gauge.
If there is a restriction in the return, why is fuel pressure dropping when it should be increasing?
I am looking for any advice to speed up the diagnosis. The flex fuel sensor doesn't appear to be restrictive.
87 GN. All stock except for TT street chip, test pipe, catback, kn filter and comp valve springs.
A couple months ago I installed brand new parts to get ready to turn the car up:
Walbro pump/sock/hose
Casper HW kit
Fuel filter
Accufab FPR with Marshall fluid filled gauge
Car ran the same. Recently I installed more parts:
Fast XFI
120lb precision injectors
GM flex fuel sensor in the return line
car is now on e85
Problem #1
I cant get the fuel pressure below 50psi static. When i put the vacuum line back on it, it quickly dips to about 48psi, then immediately jumps back to 50psi. If I drive the car for a while, the static fuel pressure drops to 45psi (line on or off does not make a difference. The vacuum source is good.
First thought here is a restriction in the return line. But ....
Problem #2
When I blip the throttle, the fuel pressure drops about 10 psi. This is dead opposite of problem #1. I suspect It is not raising under boost either but i cant see the gauge while driving. I suspect this because I had to add a lot of fuel to the VE table under boost to get the AFRs right.
Why would fuel pressure change after the car warms up? I dont believe it is a faulty gauge because I can see the O2 corrections and it correlates to the fuel pressures shown on the gauge.
If there is a restriction in the return, why is fuel pressure dropping when it should be increasing?
I am looking for any advice to speed up the diagnosis. The flex fuel sensor doesn't appear to be restrictive.