Fuel Pressure not keeping up with boost

[jamnut]

I'm running 20 PSI of boost & when I get on it the pressure goes up to about 43 PSI then falls back off to about 41 PSI. My base pressure with the line off is 41 psi & with the line on is about 36 PSI. Shouldn't I see at least 55 PSI under boost?

Right now my fuel system consists of.

Accufab AFPR
Walbro 255
I have an un installed hot wire kit.

I'm thinking that I might have a bad AFPR?? Or maybe I need to install my hotwire kit??

 

[Raist103]

Re: Fuel Pressure not keeping up with boost

sounds like a dieing pump or a clogged filter

 

[turbodig]

Re: Fuel Pressure not keeping up with boost

I'm running 20 PSI of boost & when I get on it the pressure goes up to about 43 PSI then falls back off to about 41 PSI. My base pressure with the line off is 41 psi & with the line on is about 36 PSI. Shouldn't I see at least 55 PSI under boost?

Right now my fuel system consists of.

Accufab AFPR
Walbro 255
I have an un installed hot wire kit.

I'm thinking that I might have a bad AFPR?? Or maybe I need to install my hotwire kit??

Bad pump, filter or wiring.

The FPR is less likely to be bad. Leak in the pressure line to the FPR?


41 base + 20 psi = 61. You're missing a lot of pressure.

 

[dgoodhue]

Re: Fuel Pressure not keeping up with boost

If I had to guess its the AFPR. If you have a Base FP of 41psi you should see 31-32psi at idle with 18-20" of Vacuum and 61psi with 20psi of boost.

 

[CLONE]

Re: Fuel Pressure not keeping up with boost

I'm guessing the vacuum/pressure line going to the afpr is bad or possibly (but not likely) a bad AFPR.

 

[dgoodhue]

Re: Fuel Pressure not keeping up with boost

I'm guessing the vacuum/pressure line going to the afpr is bad

Yeah I like that diagnosis better than mine...

 

[CLONE]

Re: Fuel Pressure not keeping up with boost

Yeah I like that diagnosis better than mine...

I think I've only witnessed one bad AFPR in my time (not including modified stockers). They are stupid simple and just don't seem to have many problems. But for one reason or another it seems the AFPR is not functioning properly on this truck. If it was just missing fuel pressure under boost I'd lean towards pump/filter/voltage.

We are probably both wrong Dave, but you and I seem to be thinking along the same lines.

 

[Mtn Z]

Re: Fuel Pressure not keeping up with boost

My AFPR that I bought was bad from the get go. There was no adjustment and the adjusting screw was very easy to turn. It basically wasn't adjusting anything. All I was getting was 20psi with the vacuum line off. My point is that even though it is not likely to be the AFPR, anything is possible.

 

[TYTILIDIE]

Re: Fuel Pressure not keeping up with boost

If your VAC line was bad, you would run super rich at idle and super lean up top. It usually pretty obvius. Your FP will barely move as youre driving.

 

[TYTILIDIE]

Re: Fuel Pressure not keeping up with boost

Ive experienced this same thing, it could very well be your VAC line. If its not, change your pump and filter out. And make no mistake about it, hte Walbros DO go bad.

 

[ghettosled]

Re: Fuel Pressure not keeping up with boost

pretty easy to check... with the fuel pump running turn the set screw clockwise to increase pressure and watch your gauge.. if it does not rise to 60+ psi then its the pump/filter. if it does, then check your vacuum line to the afpr... if you have a way of applying shop air then you can bench test it with the base fp and apply 20psi shop air to the afpr and hope it raises 20psi above your base. if it doesnt and your vacuum line is not leaking then check into the regulator.

fyi, you can also pinch the return line (the rubber sections) with some pliers and watch the pressure jump up due to the restriction.. basically the same thing the fpr does.

 

[jamnut]

Re: Fuel Pressure not keeping up with boost

I'm going to end up going back through my entire fuel system again. I pulled the vacuum line & adjusted the AFPR all the way to 60psi & it held, but the truck kept stalling at that pressure. I have a spare walbro from my LS1 car, I'm going to pull the tank on the sy, swap pumps & re-do lines in the pump hanger, change the filter & finally install my hotwire kit. This should be very cheap since I already have the parts, if this doesn't work, I'll swap out my AFPR. If that don't work I'll sump the tank & go with a full external fuel system since the truck will eventually be built into a low 10 or high 9 second build once my Regal is where I want it to be.

It's an odd situation, I can get into boost & the pressure will jump to around 45-50 psi then drop off to 41 psi or so, then when it goes into 3rd gear all of the sudden my fp rises back up to around 50psi. But at 18-19 psi of boost I should be seeing 57 psi or so.

There are so many things it could be including my FP gauge, it's an electronic Auto Meter not a cheap part. But it shows rock solid pressure while not in boost so I'm thinking my gauge is good.