I noticed my fuel pump making funny noises and figured my pre-pump filter must be clogged. Sounds like the pump is cutting on and off. I figured I'd change it when I swapped out the riffraff gen 1 frx for the gen 2. After the swap, I stuck a gauge on it to determine what was happening to the fuel pressure with this noise. Turns out the pressure spikes up to about 95 psi, then the fuel pump cuts off till pressure drops to around 60 psi and then repeats this process continuously.

So that makes 2 different FRX and 2 different springs in the FPR with the same problem. I even blew out the return line to the tank with compressed air (fuel cap removed) to make sure there was no restriction there. The only constant is the frx so that means it's Clay's fault, right? So I made a block off plate and got a cap and removed Clay's FPR housing but left the lines to the heads attached because the one on the passenger side is such a pain to get at. With that removed and blocked off, I basically just have a fuel crossover and I stuck my factory FPR back on and borrowed the stock spring from Barry. Looks like it's not Clay's fault because with the stock FPR I'm still hitting 95 psi at the bowl.

What could be the cause of my high fuel pressure? I blew out the return line again today using 120 psi of compressed air (fuel cap removed) and there were no restrictions I could hear. The only thing I've noticed that is wrong on my fuel bowl is there is a metal sleeve that the FPR spring and plastic bushing fits in on the bowl. Most of the time this sleeve is stuck to the bowl, but mine is loose and will fall out if you remove the bowl and aren't paying attention (learned this the hard way).

Could this be the problem or do you think I've got an issue with my return line, or what else am I missing? The sleeve piece I'm talking about is in the top left corner of this picture


I guess it's called the fuel poppet guide? Where does the rubber poppet seat go? Did I loose a piece somewhere?

 

poppet sleeve slips over the end of the poppet valve. tapered end pointing in (upstream), towards the bowl.

 

Thanks. Then yea, that's there in the right spot.

 

you are getting the spring seated correctly in the little step down inside the FPR body right. i know, it's a pain, b/c you can't really see it in the seat. and by the time you get the FPR body back on, it can slip. if the spring gets hung up on the edge of the step down, pressure will be way big.

 

Chris, Can you connect a short piece of hose to the return lines to flow the fuel into a container, that would bypass the return line just to see if there is a restriction. Just a thought.

 

Yes the spring is seated correctly. I even pulled the fuel bowl and assembled the FPR so I could verify the spring was correct looking at it from the inside of the bowl.

Good idea Bob. A 3/8" compression fitting will thread onto the return line, so I'll pick up some clear tubing and use a compression fitting to make me a dump line to see if that makes any difference.

 

Does the poppet valve move freely inside the sleeve. If you push it does it seem to stick. If it is original it may have worn enough so that when the spring pushes one way and the fuel pressure the other it could be getting cocked. Best I can come up with.

 

Everything felt fine. I guess I should order some extra fuel sleeves so I can maybe try swapping parts off the wife's truck onto mine to rule that kind of stuff out.

 

X2 with what Robin said. Sorry Chris I don't know but I am sure it will get figured out soon. I will be watching.

 

Check the poppet valve for wear issues. I found a very slight groove worn in the old poppet valve where it always slid on the bottom of the sleeve and the special poppet valve seal was very deteriorated. I didn't have your sypmtoms but installed an FPR rebuild kit when I couldn't get any of the parts separately.

 

Chris,
Did you install the FPR rebuild kit from Guzzle? When you had the FPR apart, did you try blowing through the little hole in the original poppet valve? If so, did you get air to move in both directions or only one?

In the picture attached...you will see a tiny little hole on the lower pic. That's the one I am talking about.

 

Greg, the only place I blew air was down the return line back into the fuel tank. I did not inspect the poppet valve or seal for wear marks because I did not think it would cause the pressure to spike like that.

I guess I'll take it back apart again Friday or Saturday and inspect the pieces closer for signs of wear. I had just figured worn parts would lead to low pressure, not high pressure.

 

Double post

 

Nice pics Greg.

That bottom pic shows the scoring I had on my poppet valve. It doesn't rotate so it just slides back and forth and wears at the bottom.

Also, the deformed seal looks like it's on backwards. The bevelled edge should face the other way so that it fits inside the the poppet valve sleeve.

Edit: I'm thinking the PO did or had FPR rebuilt and got the seal on wrong and that is how it got deformed. Plus the groove in my poppet valve was wider and deeper with half the miles you have.

 

I have always been curious now much fuel is returned to the tank so it will be real interesting to see what you find if you try bypassing the return line. If nothing comes out or the flow is minimal then the poppet valve might be sticking in the poppet guide. The difference between fully closed and fully open is .040", so the valve doesn't move very much at all.

Playing with my old parts, I can get the seal to stick to the poppet guide while the poppet slides in and out. If this were to happen on the vehicle then the seal would severely restrict the return fuel and result in increased pressure in the bowl. I wonder how plausible this is?

Another thing I thought about but later discounted is the idea that the poppet guide got stuck to the valve and moved in and out with the valve so no fuel was being bypassed. I now realize that can't happen because the housing holds the guide in place and it can't move in or out. There is an o-ring seal or seat on the bottom of the poppet guide and my original was rectangle cut in cross section where the replacement o-ring in the rebuild kit was round in cross section and I could not get it installed no matter how hard I tried. So, I had to re-use the original seal on my new poppet guide.

After I got it all back together, my fuel pressure was still around 95 ish so I drove around like that for a couple of weeks until I could double check my gauges. In my case the solution was a new sending unit from ISSPRO and my pressure is back to normal (around 65 psi-ish). Sounds like you have a different issue though....

At any rate, my question about the hole in the poppet valve stems from the fact that I later noticed the hole on my original part and I wondered what that was for. I wondered if it was a bleed orifice so I tried blowing through it and I could not blow downstream but I could blow upstream. So, it appears to be a check valve of some sort but I can't figure out how it works or why. I wish I would have noticed that hole when I installed the rebuild kit so I could test the new poppet but I missed the boat on that one.

Are you able to monitor your fuel pressure while driving? If so, what is your pressure at WOT under load? If it drops from 95 to 60 ish then I would suspect a sticking FPR valve. Those were my symptoms for a while and then eventually my fuel pressure would remain at 100 psi under all conditions so I think that was when my sending unit failed. I am not sure if high pressure can damage a sending unit but it kinda appears that way in my case.

Hopefully some of this info will help.