Steady 5.5psi fuel pressure drops when warmed up

[elbpony]

Good day everybody

So I have a 12-803 holley regulator between fuel filter and the edelbrock 1400. When started and cold at idle the manometer shows 5,5 and a very steady needle. It is a liquid filled gauge btw.

The warmer the engine gets, the more drops pressure. A test drive yesterday showed as low as 3 psi and a very jumpy nervous needle.
Back under the hood this morning, engine cold, i see 5,5 psi and a steady needle. Warming up just sitting in the drive way I could see the needle again lowering and getting nervous again.
When fully warmed up adjusting the regulator screw changes nothing.

Fuel filter is fine and I have no leaks

Is there another assumption than my fuel pump getting weak and old?

 

[Ricko1966]

Good day everybody

So I have a 12-803 holley regulator between fuel filter and the edelbrock 1400. When started and cold at idle the manometer shows 5,5 and a very steady needle. It is a liquid filled gauge btw.

The warmer the engine gets, the more drops pressure. A test drive yesterday showed as low as 3 psi and a very jumpy nervous needle.
Back under the hood this morning, engine cold, i see 5,5 psi and a steady needle. Warming up just sitting in the drive way I could see the needle again lowering and getting nervous again.
When fully warmed up adjusting the regulator screw changes nothing.

Fuel filter is fine and I have no leaks

Is there another assumption than my fuel pump getting weak and old?

Idk, but possibly the fuel pump sock is picking up trash partially blocking the inlet. When you turn the truck off,the pumps not making vacuum anymore the debris falls off and the pump picks up unrestricted again. Rerout your fuel pump inlet to an external gas can see if your problem goes away. Also possible the tank isn't venting creating a vaccum in the tank making it hard for the pump to draw fuel,run the truck without a gas cap,see if the problem goes away.

 

[elbpony]

Idk, but possibly the fuel pump sock is picking up trash partially blocking the inlet. When you turn the truck off,the pumps not making vacuum anymore the debris falls off and the pump picks up unrestricted again. Rerout your fuel pump inlet to an external gas can see if your problem goes away. Also possible the tank isn't venting creating a vaccum in the tank making it hard for the pump to draw fuel,run the truck without a gas cap,see if the problem goes away.

Debris, yeah good point. I ruled that out because the filter is clean. I will keep it in mind.

Gas cap, that is quick check. Thanks for the hint.
That theory matches the time related correlation of the problem needing a warm engine to pop up.

 

[elbpony]

Gas cap isn't it...

 

[Rustisbest]

I've always heard the liquid filled gauges read lower and lower as they heat up. How's it run?

 

[elbpony]

I've always heard the liquid filled gauges read lower and lower as they heat up. How's it run?

Runs perfect. But that doesn't support faith.
On the other hand, i run edelbrock carbs on stock fuel pumps for years without gauge or regulator. And never a problem...

Change for a better sometimes changes a running system and that we all know we shall not to mess with...

 

[idahovette]

Some times ignorance is bliss?

 

[xm20k]

You may not need a regulator on a mechanical pump depending on its flow rate.

I don't run a regulator on a 80GPH mechanical pump and feed dual 500s with 6psi.

 

[Grit dog]

You didn’t even say electric or mechanical pump or what kind of electric pump. Left out the most important part of the discussion.
However guessing this is not a high power motor so regardless, if it runs fine you’re not starving it.

 

[elbpony]

True, missed out on some details. It is a mechanical Pump. Besides the changed carb and the stripped out emissions stuff, it is a pretty stock original motor.

Reason for the regulator is that the carb asks for 5 to 6 psi. It was said and written that the stock pump delivers too much pressure and I thought it were good to handle it right.

The manometer showed 10 w/o regulator.

 

[elbpony]

You may not need a regulator on a mechanical pump depending on its flow rate.

I don't run a regulator on a 80GPH mechanical pump and feed dual 500s with 6psi.

The manometer displas 10psi w/o regulator. At least on paper it is too much.

 

[xm20k]

I doubt a stock pump is making that much pressure my aftermarket Holly claims 8 I get 6 on the inline gage feeding 2 4s on a tunnel ram idling at 1k rpm.

That's not running just residual after shutting it off.

You must be registered for see images attach

 

[elbpony]

Could be, a gauge probably has tolerances, too. Question is still why the pressure drops when warming up.

Probably will keep it as it is and see where it takes me

 

[Rustisbest]

Fuel Pressure Gauges: Liquid Filled vs. Dry | Verocious Motorsports

Aeromotive Guidelines for Fuel Pressure Gauges. Problem and solution for Liquid Filled versus Dry.

www.verociousmotorsports.com

You must be registered for see images attach

 

[xm20k]

Could be, a gauge probably has tolerances, too. Question is still why the pressure drops when warming up.

Probably will keep it as it is and see where it takes me

Probably heating up the fuel which thins thus less pressure.