Fuel pressure ?

racerbrad1 · Jul 10, 2007

My 96 has some frustrating problems.I replaced the fpr with a new kirban because the old regulator wouldn't move when vacuum was applied and when i piched the return the pressure sot up about 30 lbs. within seconds.
Since Ive replaced the regulator the pressure jumps about 6 lbs. with vacuum attached.

my main question is even with the new regulator when i pinch the return the pressure still jumps about 30 lbs is this normal is it possible one of the pumps is bad it has a in-tank and a external walbro pump i can hear both pumps running but maybe one of them is weak?
the car has a steady miss and when floored it hesitates real bad.
Ive replaced

2 sensor,wires,plugs,tps,and Ive cleaned the mass air.
I would greatly appreciate any help as i cant really enjoy the car with it running like this.
4.6 bored and stroked to 5.0
d1sc
comp cams stage 3 cams
ported pi heads
60 lb. injectors

9psi 98 · Jul 10, 2007

You may want to check your inline fuel filter, something is making a lot of restriction somewhere. With that setup, getting pressure shouldn't be a problem for you. I personally haven't had a fuel pump go weak on me, nor have I heard of it. They usually run 100% or not at all. I'm able to peg my fuel pressure gauge to 60psi with just a 255lph in-tank pump. I'd save it as a last resort, but checking your in tank pump's filter may be the problem. Start from the tank and work your way back to the fuel rails, you'll run into a point where there is a huge drop in pressure. Look upstream from there for the problem. Best of luck.

racerbrad1 · Jul 10, 2007

thanks for the advice I'm going to crawl under the car and check everything.I replaced the fuel filter about 2 weeks ago,maybe the fuel line is kinked ill have to check it out.The place where i got it dynoed said it could possibly be one of the pumps because depending on which one it is it could be trying to draw or push through the bad pump,i thought pumps either worked or they didn't.
What baffles me is how much the pressure still jumps when i squeeze the return line.
I'm going to check out the lines and ill report back.

9psi 98 · Jul 10, 2007

The more I think about it, if you're squeezing the return line and the pressure is jumping up 30psi maybe it's the return that's the problem. There has to be some sort of "thing" in the return that allows the pressure to build. Compare it to a garden hose. You're getting plenty of pressure from the house, but there isn't too much pressure in the hose until you kink it (like squeezing your return line) or put a nozzle on the end to slow it down. Have you modified your fuel system at all on the return side? If you've got a free flowing system that just pumps fuel from the tank through your rail and back to the tank there's no way it can build pressure no matter how much your pumps can push.

racerbrad1 · Jul 10, 2007

Okay i crawled underneath and the fuel lines look good,i went and got a long piece of rubber hose and put my gauge in the car so i could see what it was doing.

Just cruising it has 40psi and when i floor it it has 50psi,

I pinched the return line again and it jumps up to 50,if i pinch it totally shut it jumps up to 80.
I'm wondering if i have some other problem it sounds good at idle but it has no power and hesitates bad when i floor it,I'm going to try spraying it with carb cleaner and see if the idle picks up maybe it has a vacuum leak but its showing 15psi on my gauge.

i appreciate any suggestions because I'm really running out of ideas.

9psi 98 · Jul 10, 2007

Well 38psi is what it comes from the factory at and cruising at 40psi is normal, 50psi at WOT is very common. I'm running 40psi at idle just to max out my 30# injectors, 40psi while I'm cruising, and about 50psi at WOT. I don't honestly think that fuel pressure is your problem, even with the 60# injectors you have. How many pounds of boost are you running and what is your spark plug gap? I had a similar problem that I was dealing with in my car. It would run and idle fine, but WOT sputtered and ran like crap. At over 5k rpm the car would fall on its face and lose power. I had my plug gap at .034 and a guy that builds turbo cars in my area told me that my 9psi of boost was actually blowing my spark out with a gap that big. I took them down to .022 and it runs perfect now. When did it start doing all of this anyway? You didn't by any chance recently do a spark plug job?

racerbrad1 · Jul 10, 2007

I did recently replace the plugs there gapped at .032 which is what they were gapped at when i had it dynoed.
I'm running 11lbs of boost.
It dynoed at 455whp at 5800 (the mass air was maxed out)
I have a spare set of coils and wires i can try to see if that helps.

I'm also going to test for vacuum leaks,i have a reichard racing intake and its kind of tough to see the gaskets but ill try,
Its also very difficult to hear anything with the whistling of the supercharger so ill try some carb cleaner.
My check engine light was on (no mils)so i unhooked the ground to clear that to see if that will make a difference.
That problem started almost immediately after i got the car home and Ive been messing with it ever since on the dyno it would run terrible to the o2 warmed up so i replaced that also,
For the past month this thing has been driving me crazy i sure hope i can get this thing resolved.