*****Problem with dropping fuel pressure. Help*****

[Project69]

Brand new Holley electric fuel pump, pressure at idle is around 5.5-6.5psi at the carb, then after a drive and things get warmed up it drops to ~2psi. I insulated the lines that run close to any exhaust and still the same result. Is the drop to 2psi normal on a Holley 650cfm carb? Engine is a 383 from Blueprint engines.

[Ron Sutton]

Do you have a pressure regulator? If yes, which brand & model?

What brand, model & type is the pressure gauge? Liquid filled?

Is the fuel pressure gauge in the engine compartment ? ... or ?

[Project69]

no regulator, the fuel pump is for carb motors so puts out a max of like 7-8psi. The pump is mounted in the rear and its a Mr gasket fuel pressure gauge mounted on the fuel rail. It's not a liquid filled gauge.

[Ron Sutton]

Does the engine running characteristics change when the pressure gauge reads lower?

I ask this, because ... either you have a gauge that is acting up (common) ... or you have a new electric fuel pump failing but still working (not so common).

I suspect the gauge. Can you check it with another fuel pressure gauge?

[Project69]

Engine runs fine once it's warmed up even though it reads low. I'll have to get another gauge to test it. I had the same symptoms with the old pump I replaced this one with.

[Ron Sutton]

The engine won't run good with only 2 psi as you rev through the power band. It will go lean. So I think you have a faulty gauge.

[Project69]

Thanks, what's a good liquid filled gauge that mounts on the carb fuel rail? I don't want to get another Mr gasket.

[Ron Sutton]

Don't get liquid filled. They have more problems. Not sure who we get ours from.

[sam 74]

one other thing to look at is the tank, when i had a holley red pump (7 psi) with the factory tank it would drop pressure as you drive and turn especially when the level is low, the holley pumps are pushers more then pullers so they don't really perform as well as they could having to suck the fuel out of the tank. when i swapped to a sumped fuel cell the problem went away, and i also ran a return into an inlet on my filter before the pump to add a little pressure before the pump so it doesn't work as hard to pump up to 14 psi.

[MrQuick]

also what filter are you using and how a
old are the hoses?

[cornfedbill]

Do you have a filter before the pump? If so, could it be dirty?

[Flintstones]

I had a similar problem with my car many moons ago.
I had the factory in-tank fuel pump (carbed v8) going to Twin fuel filters (running parallel) with Holley blue external pump from memory (near the tank)
Upfront I had a holley regulator to bring pressure down to 6.5psi going into upgraded mechanical pump feeding Rochester 750cfm.

I had a fuel pressure gauge sitting on the bonnet and a "T" piece tapped in just before the carb so I could see what was going on.
I did multiple runs on a private track and if i tried to by pass any one of those pumps I ended up with zero pressure.

In the end with all 3 pumps running it dropped to about 4.5 PSI. It didn't make any sense why there was still was a pressure drop....

I didn't have any engine issues.
The only thing I didn't do was check the exhaust emissions to see if it was running lean under load

[Project69]

Turns out it was the fuel gauge like Ron said.