Long story, I had my 79 sitting in the driveway for about a year while I fixed up my old house prior to it sale. The house finally sold and one of the last things I had to do was move the car from the old house to the new house. A short 25 minute drive which ended about a mile up the road when the car engine kept dying on me when I tried to get up to speed. I felt like a bad fuel pump. So I wasn't going to chance it and I called AAA.

Well I brought a new fuel pump and changed it out a few weeks back. (mistake one) Test drive, same problem, over 25 mph and the engine dies. So I read the posts here and see the suggestions of possible ignition problem. I check the ignition out and the coil is not measuring within specs. It looks ok though. Well I replace the coil (second mistake). Test drive same problem.

So now I suspect the carb, stock quadrajet. I took it apart and everything look fine inside. Cleaned it out put it back on, test drive same problem. Ok, now what. So I see the posts on the sock in the gas tank. I pull the float and sock out of the tank. The sock looks ok, but I am not taking a chance. Off it went. Installed everything back. Test drive. Same problem.

Ok so now I am suspecting the fuel since the car was sitting and I can't remember when I filled it up last. So I drained the gas tank, put in dry gas, high octane gas and some STP. Test drive same problem!

So now I decide to test the fuel pressure. Which I should have done before I brought the pump in the first place. First I tried to just put it in line with the carb and saw it jump up a couple of times but most no pressure. Then I read a post on line that says you need to block the return line to get the real pressure. So I blocked the over-pressure line from the fuel pump back to the tank and guess what. The engine runs great.

Does anyone know why? the car has always had a stock fuel pump with a return line. I understand a lot of cars don't use a return line. Is it ok to run the pump like this or will it wear it out faster? My shop manual says it was installed mostly for preventing vapor lock by keep cooler fuek from the tank flowing to the carb.

 

Clogged in fuel filter, needs the added pressure to get the fuel through?

 

Same thing happened to me when my father-in-law poured old gas from a steel can (complete with rust particles) in my truck.
Clogged the filter but good.

 

I put a new one in when I replaced the fuel pump

 

did you replace both of them? the main filter, and the in carb one.

 

yes, did you replace the one in the carb, where the fuel line screws in?

 

Yes, I replaced the fuel filter in the carb and removed the filter in the tank. Since the car drives fine now it can't have anything to do with the filters. The only thing different is I plugged the return line from the fuel pump to the fuel tank.

 

Possible partial clog in the fuel line from the tank. Proper float level set in the carb, kink in the rubber fuel supply line at the pump?

 

im willing to bet theres still crap in the fuel line. check your filters again.

another good thing to do is pull the fuel line off the carb and shove the hose down a clear 2 liter bottle. crank the car over a couple times and check the gas in the bottle for contaminants.

i went through all this crap with my 69 over the last 3 years. couldnt get it over 25 with out it dieing, ran like crap, so on and so forth.

in short, my gas tank rotted out, plugged up the sock, sucked rust through the main lines (which were also heavily rusted) got crap stuck in the fuel pump, both filters, and carb.

i replaced the tank, sending unit, main lines, filters several times, and carb. a couple weeks after this i had to change the filters again because of all the loose crap that was still floating around in the system and plugged the filters. it took a couple hundred miles to get it all out of its system.

 

Check the S shaped fuel line that runs from the metal line on the frame to the pump. If it's kinked at all you won't get good fuel flow or if it's to soft the pump may be sucking it closed when you step on the gas.