chris712vt
15+ Year Contributor
- 524
- 6
- Mar 27, 2006
-
SLC,
Utah
Alright guys, I'm stumped on my "unadjustable" fuel pressure right now. Let me explain my setup, and what I've tried so far.
I think most of my mods are up to date in my profile if you need to reference that, but my fuel system consists of (95 fuel system) a Walbro 255 high-pressure, stock supply lines all the way to the rail, 450cc injectors, 97 fuel rail (eliminated stock fpr) with -4AN outlet, -6AN return line to SFMU, then SFMU's return reduces down to a 1/4" hose and back to the stock return line on the firewall.
I bought the SFMU from a 2GNT member who previously used with with 450s and 16psi, pretty much my setup, so I didn't change anything on it. When I first started the car it didn't idle well, but smoothed out after a minute and a little revving. I checked the fuel pressure and it was 42-45ish psi, with the vacuum line connected.
I tried loosening the fuel pressure screw on top, in fact so loose the screw came out, and the fuel pressure didn't change at all (but it did increase a little when I tightened it all the way down). I unplugged the vacuum line and it didn't change. I put in the little in-line vacuum reducer thing and that didn't make a difference. I tried keeping the bleed valve all the way closed, and fully open, neither made a difference. The fuel pressure just stayed at 40 some psi every time.
I decided, well 40+psi idling under vacuum or static pressure with 450s just means I'm running rich as hell, but it won't hurt the car. So I took it for a quick test drive down the street and back. It pulls hard and feels great once I hit some boost, but I need to figure out how to drop that fuel pressure down. Also, I've noticed when I first start it up after it's been off for a while it sounds like it's running on 3 cylinders, but once it warms up, or I rev it a bit, or I hit a little boost, it goes back to being normal and strong - I assume that's an effect of running so rich and possibly dousing the plugs with fuel on initial startup.
Anyway, here are a couple pictures and two videos (one shows startup and fuel pressure gauge, the other shows the test drive). Anyone have any advice or ideas as to why I can't get the fuel pressure below 40psi? I'd like it to be more like 20.
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I think most of my mods are up to date in my profile if you need to reference that, but my fuel system consists of (95 fuel system) a Walbro 255 high-pressure, stock supply lines all the way to the rail, 450cc injectors, 97 fuel rail (eliminated stock fpr) with -4AN outlet, -6AN return line to SFMU, then SFMU's return reduces down to a 1/4" hose and back to the stock return line on the firewall.
I bought the SFMU from a 2GNT member who previously used with with 450s and 16psi, pretty much my setup, so I didn't change anything on it. When I first started the car it didn't idle well, but smoothed out after a minute and a little revving. I checked the fuel pressure and it was 42-45ish psi, with the vacuum line connected.
I tried loosening the fuel pressure screw on top, in fact so loose the screw came out, and the fuel pressure didn't change at all (but it did increase a little when I tightened it all the way down). I unplugged the vacuum line and it didn't change. I put in the little in-line vacuum reducer thing and that didn't make a difference. I tried keeping the bleed valve all the way closed, and fully open, neither made a difference. The fuel pressure just stayed at 40 some psi every time.
I decided, well 40+psi idling under vacuum or static pressure with 450s just means I'm running rich as hell, but it won't hurt the car. So I took it for a quick test drive down the street and back. It pulls hard and feels great once I hit some boost, but I need to figure out how to drop that fuel pressure down. Also, I've noticed when I first start it up after it's been off for a while it sounds like it's running on 3 cylinders, but once it warms up, or I rev it a bit, or I hit a little boost, it goes back to being normal and strong - I assume that's an effect of running so rich and possibly dousing the plugs with fuel on initial startup.
Anyway, here are a couple pictures and two videos (one shows startup and fuel pressure gauge, the other shows the test drive). Anyone have any advice or ideas as to why I can't get the fuel pressure below 40psi? I'd like it to be more like 20.
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