Mechanical and electrical fuel pump question

[mopar440cu]

I have a 1979 CJ5 AMC 304 with a mechanical fuel pump and my fuel pressure reading is really erratic and low. The reading goes between 2-3 @ idle speed. The pump was purchased last year, but it would not surprise me if it went bad. So, since it was giving me fits trying to start and low pressure, I decided to place a in-line electrical fuel pump close to the fuel tank and run it from a switch on my dash. Well after all was hooked up, filter changed, I let the pump run for a few seconds, shut the pump off, then attempted to start it. It still took too long starting it, plus the reading never changed 2-3 @idle. My next step was to keep it running and switch on the electric fuel pump and see how she ran and what the gauge said. Well, too me surprise, the engine RPM raised up a little and the reading was right around 5-5.5. Weird?? My question to yall is can I run both the mechanical and electrical together or should I do just one? I understand there is a debate over which to use, but that can of worms I don't want to open at this point!

 

[Torxhead]

You could have an issue with the fuel tank vent system not breathing correctly or possibly cracks in the outlet line from the fuel pump. With a AMC 304 , a mechanical pump should be just fine by itself. Properly setting up an exterior electrical pump is a bit complicated as the fuel must be siphoned to the pump requiring the pump to be placed at the lowest position possible or the pump can be placed as close to the tank as it can. Again a properly vented fuel tank is required. When either of these types of pumps run with a less than optimal amount of fuel in them it can damage it.

 

[caveman]

Yes. You can run both at the same time.

 

[Lumpy Grits]

How does the Jeep run?
2-3 psi at idle ain't bad for a mech pump.
Are you using the OEM type fuel filter with the fuel return line built in?
When was the last time this fuel filter was changed? Where are you measuring the fuel line psi?
LG

 

[mopar440cu]

Pardon for not getting back quicker but, I am not getting notification of any responses from this site. Strange? Anyway I decided since I had an extra Holley Red electric fuel pump and regulator here in the barn from another build, I would cut through the chase and add that instead of having a Carter pump near the tank and a mechanical fuel pump. I just put the red wear the Carter was, basically, eliminated the mechanical and have NO issues. "Knock on Wood" as they say.

 

[Lumpy Grits]

THX-BTW: Ck you SPAM file for the notices.
LG