Fuel presssure drop

[brickyard69]

I have a 1969 Camaro with all new tank, lines, motor, pump, and carb.

The car ran fine (100 miles) until recently.

Now it will start fine with 7 psi fuel pressure. After a 10 minute drive the car will start to die and have fuel pressure between 0-3 psi.

I tried swapping pumps and it still does it. The pump I swapped was used and I assumed it was good, but it may not be.

I removed the line from the tank to pump and notices that fuel trickled out (not poured).

I removed the tank to ensure that the "sock" was clean and there were no obstructions. There were non as everything is new.

I put my finger over the inlet hose from the pump. Should there be suction? There was none.

Any suggestions?

[HILROD]

What kind of pump, and where is it mounted?

[68Formula]

Real quick, sounds like you might have a heat soak issue. Make sure all the lines are away from heat sources as much as possible. Maybe even try insulating the line.

[brickyard69]

That is exactly how it acts.

Or like it does not have enough fuel in the tank.

I was expecting to see the sock messed up, but it is as clean as can be.

I did hook up a vacume pump to the engine compartment side of the steel fuel line. I would think that I would get a steady dtream. Instead it is about half that.

[brickyard69]

It is a Carter mechanical pump.

[brickyard69]

The more I read, it sounds like vapor lock.

The strange thing is, is that it is only 50 degrees out. Also the only line close to the exhaust is the rubber one that connects the tank to the body line.

How should I test this?

Should I install an inline electric pump?

[68Formula]

I once had the problem because the line was too close to the valve cover. Fixed it using a swivel connecting at the carb inlet and bending the metal portion up so the flexible hose was even with the carb inlet.

You can test it using an insulating sleeve or temporarily routing it away from the exhaust and heads (zip ties?).

If the problem is repeatable at idle, you could get the engine warm, and then hook the pump inlet to an external tank (TANK OUTSIDE AND AWAY FROM ANYTHING YOU DON'T WANT TO CATCH ON FIRE). At least then you know if the tank is contributing.

[Tech @ BG]

It can be a problem with your vent. Make sure the vent is open on your tank, if you don't get air into the tank fast enough to replace the fuel as it's drawn out you will get a vacuum in the tank making it extremely hard to draw fuel out.

[brickyard69]

It is a new tank and cap.

I have tried to run it with the cap off and not much difference.

It is hard to duplicate, bacause it does not happen until the car runs and if I take it out then I am stuck.

I did notice that the pre-bent fuel line runs real close (i inch) tio the header.

I have insulated it and I will try that out for now.

I'll let you all know if vapor lock was the problem.

Thank you for all the advise.

[MonzaRacer]

does the cap say "vented" or "non-vented". I would say its not venting.

[brickyard69]

The problem WAS vapor lock.

The 1969 standard pre-bent fuel line that runs along the sub-frame was only one inch away from the header pipe.

I relocated it and covered it in heat shild material and it seams fine now.

I am doing an all day track event this week, so we shall see.

[68Formula]

The problem WAS vapor lock.

The 1969 standard pre-bent fuel line that runs along the sub-frame was only one inch away from the header pipe.

I relocated it and covered it in heat shild material and it seams fine now.

I am doing an all day track event this week, so we shall see.

Thanks for the feedback. Always nice to hear the end result. Have fun at the track.

[brickyard69]

Car was fine at the track but when I got home I went for a ride.

I problem happened AGAIN when I idle for a long time.

The fuel pump feels very hot, but that should not be an issue as many cars run headers and a mechanical pump.

I am thinking of converting to an electical pump, just to try that.

Any other suggestions?

[Steve68]

Check into pumps, you don't want a holly Blue pump on there if you like it quiet! there screamers!

[brickyard69]

I need to determine if it is before or after the pump at this time.

I plan on using a heat spacer on the pump, relocating and covering all my fuel lines in heat wrap, and putting a plate under the carb.

I still think it is before the pump, but no lines are close to a heat soarce. The pump itself seams to get very hot, so I will use the heat spacer.

Any other suggestions?

[brickyard69]

I have issolated the problem to the mechanical fuel pump getting to hot.

If I let it idle and get real hot the fuel pressure will drop to zero and the engine will die. If I wait till it gets low and pour some water on the pump the pressure will shoot right back to 6psi.

I have two pumps and they both do it.

I can either try one of those BG heat spacers between the pump and the block or go to an electric.

I have a new Holley Red pump so I may go that route.

Where do you mount it to get it below the tank on a 69 Camaro?
It seams almost impossible to do so.

[Rick Dorion]

What pump? I have had two carters and not seen this issue. My fuel line also runs close to a header pipe.

[brickyard69]

I have tried a Carter and a Holley and they both do it.

[Azzkikrcuda]

This is a good post, my buddies camero is doing the exact same thing.

[gordonquixote]

This is a good post, my buddies camero is doing the exact same thing.

Mine too - right now.....

I have a '71 Camaro with a 396 and a new Holley mechanical 120 gpm pump with new lines and new fuel filter.

I fire it up and I have 6-7 psi when it's cold, I go out and drive it and come back and the fuel filter is empty and I have no pressure on the fuel pressure gauge. The car runs but won't idle.

I am running out of ideas myself.