Just installed a holley blue, and the fuel pressure is erratic, 14 psi at idle and fluctuates during cruising or WOT anywhere from 9 to 12 psi. removed stock LP and plumbed Holley to fuel cannister with 1/2 inch line. i used the wire harness from the stock LP to run the Holley. I'm using a electric Autometer fuel pressure gauge that worked great with the stock lift pump, but reading erratic with the holley. any help would be greatly appreciated!

 

You might want to check all of the electrical connections on the pump and for the gauge. Also check to make sure that you dont have any leaks.

 

You may need a relay between the stock pump harness and the Holley. The Holley pulls more juice than the stock and I have read on here that the stock pump had a variable voltage supply. I have a relay between and my pressure only seems to vary by throttle and fuel viscosity.

 

Also, pull the bypass plunger out and LIGHTLY rub it down with VERY FINE sandpaper or emery cloth and also rub the bore itself down. Sometimes they got hung up a little bit.

 

What kind of relay is used? part number? and where can it be found, I think I have read the the stock pump used pulse wave modulation? So the erratic needle movement would be from the the pulse from 0 - 12 volts...

 

Just go to radio shack or o'reilly's and pick up a 30 amp relay. Their cheap. Run a wire from the battery to the relay, a wire from the relay to the positive on the pump, a ground from the relay to the frame, and then use the factory lift pump power wire to trigger the relay. I've been doing this for 2 years now and it's working great. I have 15 at idle, 14 cruising, and 11 at WOT with 100+hp injectors and a comp in EZ mode.

 

BigBlue
Are you using the holley blue also?

 

Yup. Been using it for 2 years now and it's still holding 15 at idle and 11-12 at Wot with 100+hp injectors and a comp in EZ mode.

 

Installed the relay, and I still have an erratic needle bounce. I'm going to try to clean the bypass plunger and bore next.. Any other ideas? I noticed the votage varies from about 14.47 to 13.07 when the truck is running. Could this voltage variation causing the pump pressure variation...

 

I was hoping you were going to have this fixed by now but as you dont I'll tell ya what I did to fix mine.

I did the spring stretch/ compress deal ran new wires to a 50amp realy, ran all new hoses.

Then.. Ready for this?

I installed a F.A.S.S and the pulsating went away.

Seriously I went through three Holleys and all the above and decided the VP was WAY to expensive to risk it.

dan

 

FYI,

I run my holley blue off the stock lift pump power wire, and yes my stock lift pump is sitll hooked up. Relays are nice, but no need for one. Been running 100k miles like this.

IIRC the lift pump is run off the computer, which has the power wire internally limited to 5 amps, no fuse involved.

 

Bad autometer sender?

Do you use a snubber before the sender?

Autometer tech support can discuss both with you.

 

Thank you I will try autometer tech support.

 

No i did not use a snubber before the sending unit. Where can i can get one? should i try a needle valve?

 

"which has the power wire internally limited to 5 amps, no fuse involved."

I'm not sure about that.

And if that is the case, there isn't enough current to run both the Holly (3A+) and your stock lift pump.