Fuel pressure

[alextucker]

I recently fitted a pressure gauge when putting in new braided fuel lines from the pump to the carb and mounted the larger style fuel filter. I know I should be getting 5-6psi when running which I am but should this pressure bounce up and down and totally die after the engine has been off for a few minutes?

 

[hashmaker]

I don't think it should bounce as the pump strokes, it is doing what it should in maintaining pressure. As for bleeding off if the fuel has gone past the pump then it is on the pressure side, no longer on the suction side. So if it bleeds off it would have to go back thru the pump or on thru the carb which of course would flood the engine. It might drop off a little over night but holding some pressure is good.

 

[Mopars & Missiles]

Yes, it will bounce. It is a diaphragm pump, not a constant pressure pump. It pumps in "pulses". It will normally bounce about a half psi at idle, maybe slightly more. At higher engine speeds, the pressure should become a bit more constant since the pulses are faster, closer together. The pressure should hold for a little while once you shut the engine off. There supposedly is a check valve in the pump that prevents fuel backflow, although it will leak back slowly after a few minutes with the engine off. Some leak back faster than others.

Sounds like your pump is working just fine to me.

 

[khryslerkid]

Carter M6903

 

[Mopars & Missiles]

Carter M6903

Perfect demonstration, thanks Kid!

 

[alextucker]

Excellent so it's performing properly, although not as neat looking as the Kids, I thought I might have a leak since the pressure dies off when it's not running for 30 mins or so. Good to know this is normal. Another lesson learned, feckin love this forum.

 

[Fran Blacker]

The seals in fuel pump would have to be perfect to seal the pressure. Gas will find the smallest imperfection. They are only rubber flapper valves.