Is my fuel pump bad if pressure drops quickly after shut off?

[WH23G3G]

I started my 73 Charger 400-4bbl today. Over the winter months I added the Edelbrock insulator gasket a new fuel filter, and a new silicone hose from the pump to the carb. I had to remove the carb to install the insulator gasket's extended studs and I haven't even started the car since Thanksgiving when we drove it around and it stalled out. So today it started up with very little effort at all, two pumps of the gas pedal and a couple turns and it fired right up and stayed running. Although it was pretty mild tonight when I started it. I only let it run for about 5 mins or so but I checked my inline fuel pressure gauge while it was running. It was at 7psi. After I shut it down I noticed the gauge started to drop quicker than on my 65 Valiant Slant Six in which I have installed the same fuel pressure gauge, whereas it stays at 5-6psi and does not go down quick after I shut it off. I remember reading somewhere that if the fuel pressure drops quick after shutting it off it may have a leaky outlet valve or something? Could that have contributed to why it was running so bad and stalled out when we drove it over Thanksgiving and when I drove it last summer and it stalled out without warning in the summer heat? I have a new fuel pump but didn't install yet because I wanted to check the pressure which is good but I know it dropping pressure quick after shut off might be bad. Or did I not even let it run long enough for this to mean anything?

[A383Wing]

could have leaky needle & seat in the carb also

look for fuel drips in the carb after shut off

[moparsr2fast]

 7 psi is a bit on the high side, although I couldn't say if that has any bearing on the quick fuel pressure drop or not. 

[John_Kunkel]

The valves in most mechanical pumps are metal-to-metal (no rubber seals) so I wouldn't expect them top hold pressure for very long after shutdown.

[WH23G3G]

I checked the 73 factory Chrysler shop manual and it does indeed say that if the pressure drops quickly down to zero after shutdown suspect a leaky fuel pump outlet valve. Also I checked the specs on the 400 and 440 it said fuel pump pressure should be between 3.5-5psi. Mine was at 7psi. I checked the new fuel pump I have here that I haven't installed yet, it's an Airtex 6415 which has a max fuel pressure of 5.5psi. I don't know what pump I put on when I had the motor out to rebuild years ago, probably the same. I might have the same guy that helped me on my Valiant come over this weekend and take my Charger for a drive and see if it shuts off when it gets hot or if there is any problems right away when we take off. Now from the filter to the Edelbrock carb I'm running a 3/8 silicone hose and the inline fuel pressure gauge I have is right before the carb fitting. Will that make a difference in the high pressure? So 7psi is a little high for the 400 and the low-performance 440. The 440 HP had a spec of 7psi according to the Chrysler shop manual. Hey what about those factory 440 vapor separators at the pump, do they help with vapor lock? Could one be installed on my 400? Where does the bracket mount to?

[ZekesGarage]

It seems the Edelbrock carbs are a bit picky about fuel pressure, and 7psi seems too much for them, it will blow past the needle valve and potentially flood the engine. I do know Edelbrock makes a specific fuel pump for their carbs that are about 5-6 psi.

Coming from the GM side of the house, most Quadrajets and Holleys seem to run fine forever at 7psi, and the size of the engine doesn't have any real bearing on pump pressure, only how much flow it needs depending on load.

When the car stalls, does it start back up quickly, or do you have to turn it over a lot to clear the engine like it's flooded? If it seems to be flooded, you do need to take a look at your idle mixture, and if it's not too rich the pressure might be causing the needle valve to unseat and flooding it. Consider putting a lower PSI pump, or regulator on it to keep it in the 5psi range for that carb.


Good luck with it

Shawn