I'm begining to wonder if I'm nuts with this fuel pressure problem...

Here the sob story...

I have a walbro 392, at WOT I pull the pressure from 30+ PSI to 0. I hold a solid 30+ PSI until I stand on it. I can be at 3/4 throttle and see no drop in pressure. Once I let off, the FP shoots back to 30 PSI, it is not laggy.
I have replaced the lines from the out side of the pump, new bypass. I have 3/8ths line from the tank to the ff canister.

I am about to pull my tank to see if I am having problems in there, but I cannot imagine what it could be. This happens when my tank is full or empty.

I pull my pre filter and fuel runs through it freely, it's not clogged. I have changed it a few times... no love.

I am wondering if I am actually demanding more than the pump can supply, but I know guys with trucks that are modded more than mine, and they run the 392 with no problems.

I have flow tested the pump, I am getting a gallon of fuel in about 52 seconds.

So, do I need a pump that can flow more volume, or do ya think that there's a line problem? I don't want to drop the tank, that's a pain in the rear...

Thanks, DTR!

 

I would think if you had huge injectors this could be a problem. I don't see what you have but, as you said... I have a few more mods and have never lost more than a couple psi in pressure on my single walbro. I run at 12psi and only sometimes I'll see it drop to 10. I do have duals but, they don't use the fuel. My, around 100hp injectors use a bit of fuel but, not enough that the walbro can't hang.

Did you do a big line kit with the walbro ? sorry, not much help I know.... IMO, I don't think you're using enough fuel to drop your psi that much so, I don't think it's the pump.

 

Thanks, Ty. Yeah, I have the big line kit. Never had this problem when I was running the stock fuel pump in series... Stock injectors.

12 psi? WOW! That's all? I know it's more of a volume thing than a pressure thing...
Where do you take your reading at? I've seen your set up, it's nice.
Triton's set up...

 

duals don't need a lot of psi. The Bosch CP3 doesn't really even need a lift pump as it works on suction. I suppose a little psi helps things along. I found when running my truck stock... I only needed 20 to 22 psi out of the walbro for it to run smoothly. I never saw it anywhere close to zero but, it did drop a few psi. The pump is one of the first things I did.

I take the FP reading off the OEM filter lid.

It could be a voltage thing. Do you have a good ground at the pump ? Don't know that it would help but, it's easy enough to do.... try using some lower psi shims in the pressure regulator. 20psi should be fine. Here's some spec on a walbro...

 

Tee a vacuum gauge into the intake line just in front of the pump. Run it to someplace an observer in the cab can see it and do your WOT run. The gauge will tell you if you have some sort of restriction on the intake side of the pump.

 

That's a good point, Treefarm.

Ty, if I understand what you are saying... it will flow a higher GPH at a lower PSI... but If I understand the pump right, it's flowing at it's max setting all the time, (which is only like 15% of the pumps capacity) but the bypass says how much pressure that you have. What I'm getting from this, if the truck is demanding more fuel, less fuel goes throught the bypass. If the FP is less than what you have the bypass set at, them there should be no fuel going through the bypass at all.

I'm gonna go check the wires, change the FF again...

I read my FP where the adapter from the stock LP bolts onto the ff canister.

Hey, Ty, where did you get that setup? I like the SS braided line. How far does that run? Just to the filter, or all the way?

Thanks, guys...

mad

 

Try reading you're fuel pressure at different points to find where it drops.

 

I know where it's Droppin!

Maybe I should read it at my ff lid again... see what that says. If not, I gotta start taking readings else where.

 

I don't know about the less pressure the more the flow but, according to the pump specs... it flows more with higher voltage put to it. Don't know how this works though... maybe the ECM sends lower or higher voltage from what the TPS tell it ???

If you have a older SS filter lid, FYI... if you didn't already know... the new filters won't let fuel by it to get a reading. You have to notch the top of the filter to let fuel by. I believe their newer lids have been machined a bit more to avoid this problem.

If you have you regulator set at 30psi... you have a ton of fuel returning to the tank. I think Richard sends out the pumps with a 22psi shim already in place cause that's what he and others have found to be a optimal pressure on a stock set up. It probably only takes a few psi to run the truck so, all the rest is being returned. At WOT yes, less will go back but, to use 30psi I'd think you'd have to be running some massive injectors

 

Ya, I didn't think that I would be using all the fuel that the pump could give me...

Ya, I'm running it dry from 30 PSI...
I'm about to go play with it, I'll post results...

 

Not knocking Richard's design at all here, but that checkvalve return setup isn't the best way to run things, imho.

I was one of the first Walbro guys way back when and I tried many different setups starting with a little bypass line from the cp3 feed looped to the return side of the cp3. Then I had a custom made swagelok checkvalve made. Everything I did worked to some extent but there was always a drop at wot.

Now I run an Aeromotive universal bypass valve. Whatever I set it at, it stays there and doesn't move from idle to wot. Obviously this is the ideal setup if you're worried about consistent pressure at the cp3. Thinking about it, I'd of saved a ton of money and time if I'd have just gone this route from the beginning... Live and lern I guess.

 

A vacuum gauge on the input to a lift pump tells you the condition of things downstream. If you pull a high vacuum, it is because the fuel is being restricted by something. They are sometimes installed permanently to tell you when to change the filter between the tank and the pump. Racor even sells one that mounts directly on one of their filters. It can also be remotely mounted. I had one installed on a diesel powered boat of mine.

In your case, it would tell you if the problem was in the tank or the lines between the tank and the pump.

 

Raserfrazzer... I didn't get to it this afternoon. I'm gonna check my voltage, reduce the pressure to about 20 psi, and make sure that I do not have any leaks. I've always had a little seep around the pump, but not a drip....

Ok, it's time for a beer...

 

Based on your measurement of GPH, you are around 60gph. AIrdog and FASS start at 95/100 GPH and generally run around 16-18 psi. Any decent positive pressure is good for the CP3. Hard to say for sure, but it sounds like a volume issue to me.

 

Yeah, volume...

Today, I went WOT with my edge on 3 and the MP-8 on 50%, pulled it down to about 25... when I turn it up, tho...

Ty, If your dual CP3's are pulling a a vacuum, then it's helping the pump... ???