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Fuel pressure reads low

T

Timgoheen

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I got this blazer running that was sitting for years. It has a holley 600cfm dual inlet carburetor. I put a new spectre guage on the fuel rail. I have replaced the fuel tank and sending unit. I have installed a brand new Carter P4070 pump which is getting a full 12v on its own circuit, with dual relays. I have changed the filter twice now. I have blown air through the steel lines and replaced the rubber sections. It seems to run ok. Not great, but ok. The guage sometimes reads just over 2psi. Most of the time it reads 0.
Any ideas ? Should I relace the gauge again ?
 
My money says the pump sucks. By far, the majority of “inexpensive” pumps are junk. Combine cheap quality with the fact that most aren’t plumbed in a way that keeps them primed (they are pushers, not pullers) they die an early death because they have repetitive dry starts.
 
nvrenuf said:
My money says the pump sucks. By far, the majority of “inexpensive” pumps are junk. Combine cheap quality with the fact that most aren’t plumbed in a way that keeps them primed (they are pushers, not pullers) they die an early death because they have repetitive dry starts.
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I have it mounted on the tank shield, front side as low as possible without hanging down past the shield. From what I have read, this is supposed to be a really good pump.
 
External pumps still have to draw the fuel out of the tank no matter where they’re mounted. Unless you’re using a tank/cell with fittings on a sump the pump has to pull fuel up the draw stew on the sending unit before it goes downhill to the pump, gravity dictates that section of fuel is always dry on start up.

I’m not hatin on you, just talking about the downfalls of external pumps. Even very expensive high end Holley (etc) pumps will eventually die because of being run dry repeatedly.

All that said, you can “borrow” a fuel pressure gauge kit from parts store loaner tool programs, maybe get another gauge and tap in to the line at the pump and see if the pressure agrees with your other gauge. If the pressure is low at the pump it’s got to be that since you’ve cleared the lines.

Does the pump have a warranty? Maybe check the pressure on the current pump then swap it and compare to see if there an improvement.
 
i have the Holley red label mounted similar to you it runs 6psi all day every day. Also it runs through a regulator with a return to tank. Last pump I ran dead head and it failed early, 6 months, but was Edelbrock rotary pump.

possibly the gauge is misreading ?
 
It's deadheaded. At this point, I'm pretty frustrated with the fuel system. I'm not sure which route to take. But I will try a different guage, and I will be creating an acces door.
 
The only luck I’ve ever had with the old carbureted systems was using a stock(read: mechanical pump, mounted on the front side of the engine block)
I’ve had some fail, but, over all, they’ve performed satisfactorily.
I always went with good brand name, also.
 
Since you’re looking at that rabbit hole….

I have a 91 Blazer and I’m using the original TBI tank and internal pump on a carbureted 454 with return style regulator. Knock on wood, this set up has been super dependable.
 
So, I finally have fuel pressure after replacing the gauge, then going to the Holley blue fuel pump and regulator and finally today replacing the last bit of original hose, which seemed to be the problem.
Now I have too much pressure. I regulate it down to 5.5 and it keeps shooting up to 11 and slowly backing down then shooting up again.
Too much pump now ? Any ideas ?
 
What regulator are you using? Are you sure this pump and regulator are designed for deadhead?
 
Yes, deadhead is one of the setups in the instructions. The regulator is the holley one that they pair with the pump in the kit.
 
I once had a speed shop owner tell me that the base Holley regulator that came with the blue pump were fine, “we put 2 inline and they work great”. :eek1:

I run a factory TBI pump with Holley billet return style regulator and the pressure is rock solid at 7 psi, it drops maybe a 1/4 of 1 psi at WOT.
 
blue pump is good for almost 30psi, red pump is less than 9. I use red with Holley regulator and return to tank, rock solid 6 psi on the cheap Summit gauge
 
My 77 came with a mechanical pump that had a return to to tank, with a 1/4 id line back to tank factory. Holley part #12-881 is the regulator I am using.
 
So, I chand it to the red pump with the holley 803bp regulator going back to the tank. I get 7psi now, but still cannot get any adjustment out of the regulator- screw completely out and no change. The only thing that I can think it is now is a restriction on the return line. The return line is all new -6 to about a foot of 3/8 rubber hose to the 3rd pipe coming out of the sending unit. Is that pipe the correct one ?
 
One is ½" to fill vent. Another ⅜" feed. The 3rd is either vent to evap canister 5/16ths or a fuel return to tank ¼".
I believe you'll have 4 connections with the return.

The 5/16" should be adequate, I am using the ¼" and gauge reads 6psi and the regulator screw has no effect.
These inexpensive 3/4" gauges are probably not that accurate.
How does it run? Is carb dribbling fuel in the venturis?
 
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