Crazy fuel issue that’s got me stumped…

[450bench]

…fairly new Holley red electric pump mounted in the back. Pressure at idle is about 6. Holley 870 carb.
Changed my plugs and wires and while I’m setting the idle mixture I notice fuel pressure down to around 3. Never noticed that before but it could why suddenly I’m running super lean. Plugs are like they’ve never been run. A lot of hesitation suddenly.
The guy I got the car from wires the pump to where it comes on when the engine is running, which I thought was weird. Cut it off and cranked it again. Pressure a 6.
I went under the car to see if the pump was hot to the touch and it was fairly warm but not outrageously hot.
Could it be a voltage thing? Bad regulator? Crappy pump? I’m stumped. Anyone ever experience this?

 

[muscl car]

…fairly new Holley red electric pump mounted in the back. Pressure at idle is about 6. Holley 870 carb.
Changed my plugs and wires and while I’m setting the idle mixture I notice fuel pressure down to around 3. Never noticed that before but it could why suddenly I’m running super lean. Plugs are like they’ve never been run. A lot of hesitation suddenly.
The guy I got the car from wires the pump to where it comes on when the engine is running, which I thought was weird. Cut it off and cranked it again. Pressure a 6.
I went under the car to see if the pump was hot to the touch and it was fairly warm but not outrageously hot.
Could it be a voltage thing? Bad regulator? Crappy pump? I’m stumped. Anyone ever experience this?

Are you running those small inline fuel press guages ???? , those have been found to be very inaccurate

Are running a fuel pump relay to make sure the pump is getting full power ???

 

[450bench]

Gauge is on my fuel log by the carb.

I haven’t changed the wiring. The guy has it run to the fuse box and it comes on when the engine is actually running. I don’t like that.

 

[450bench]

Apparently the guy who had the car before me wired the pump to come on when the car is cranked and running. He must have run it through the fuse box. What spade would he have used? Ign spade?

 

[xten]

It's weird that the pump doesn't come on in the "ON" position. Does the hot wire have a relay as Chuck mentioned? That's what helped my problem. The yellow/orange light for low fuel pressure in my nitrous controller used to come on at high RPM before I put the relay on. Also I've had those gauges not read right when warm.

 

[Ihada70Z28B4]

He could have wired it through an oil pressure switch, so that the pump shuts down with the engine in case of an accident.

 

[Ratty_81]

I just went thru this recently, but my fuel pressure would only drop during hard accel, freeway on ramps. "Spirited driving" usually, but sometimes just cruising on the highway.
Pulled my hair out checking the fuel filter, changing pumps, etc. I disconnected the fuel line at the carb to drain the tank and when I turned on the pump, it barely trickled out. Turns out my Earls sintered bronze filter was full of non visible crap causing a restriction. Threw in a plastic see thru unit and it ran like a champ.

 

[450bench]

Yeah those brass filters are bad news. The stock one in holleys are a great example of how you can starve an engine.

I may have fixed my issue. When I installed the pump, it appears my hot wire connectors was barely connected. Literally.
I took it out and spliced in a better wire with much better male/female ends, then wrapped them in small rubber line to protect them.
Drove the car tonight and you can notice immediately that it runs like I put a new motor in it. Now the plugs are nice and tan and acceleration apppears to be great.
Hope so at least.

 

[Grumpy 427]

Those holley pumps are garbage period. Go back to a 120 GPl mechanical pump and enjoy.

 

[1980RS]

Had a Holley blue pump do that in the late 80's. Never did figure out why the damn thing would loose pressure. What fixed it for me? a new Mallory Comp 140 pump, ran it on the car for 30 years until I put a Comp 250 pump on the car. Never had a lick of trouble with Mallory stuff. Most Holley electric pumps are junk IMO, they either leak or fail.