car stalling

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mattmatthew

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some background info:

slant 6, carter bbd carb

recently changed fuel pump (diaphragm was broken on old unit and leaking fuel into the motor). changed out flex line between hard line and pump. also changed the oil (it was thinned out with fuel).

recently cleaned carb, and when putting back the top half accidentally pinched the accelerator pump neoprene cup. because of that, stalls when pedal is floored, but was running fine at idle, normal speed, etc.

yesterday i was driving it on the freeway, and it was running fine, suddenly the power cut out. it did that 3 times, traveled about 500 ft. the fuel filter would fill up with gas, and the car would run for a little while. but then the fuel would visibly drain out of the filter, and the motor would shut off.

checked the fuel pump (and the new flex line) for leaks... none. could it be leaking out the back, near the tank?
 
- Cracked rubber line from the tank to the main hard line, allowing air to be drawn in
- Plugged fuel sock in the tank due to crud in the tank
- Bad new fuel pump
 
i cranked the motor and got the fuel to pump into a bottle. but, when i let off the ignition, the rubber hose sucked the fuel back down the line towards the pump. pretty quickly too, i might add.

i rechecked the connections at the fuel pump. additionally, i checked along the hard line aft of the pump as well as the flex line to the tank. no leaks or drips anywhere.

when the car is being cranked, the pump seems to be pretty strong. i get a good amount of fuel coming thru the line.

my mechanic friend explained there's a check valve inside the fuel pump that ensures fuel flow in only a single direction.

if the check valve is working properly... my reasoning is that even if there's a problem aft of the pump, the one-way valve should prevent fuel from going back down the line, and fuel should remain in the line even if the car is not running, and the filter should subsequently remain full.

do you think the check valve in the fuel pump is the culprit? i'm going to have napa swap the pump tomorrow. but i want to hear your ideas as well.
 
actually i'm wondering if there might be multiple issues. clog at the sock in the tank as well as a bad check valve.
 
i cranked the motor and got the fuel to pump into a bottle. but, when i let off the ignition, the rubber hose sucked the fuel back down the line towards the pump. pretty quickly too, i might add.
Click to expand...

Just for giggles, remove your gas cap and try that again.
 
oh yeah, i did remove the gas cap. same result. a little slower, but it still sucked the gas right out of the bottle.

what's the theory behind that?
 
Your mechanic friend is 100% right; there are check valves at the inlet and at the outlet. Sounds like both are stuck open for the fuel to be sucked back. (In particular, you can test the outlet vavle with it hooked to the carb; pressure ought to stay in the line between the pump outlet for quite a while after the engine stops turning if the needle valve and outlet valve are good.)

And possibly the pump diaphragm is busted and the fuel is draining back into the crankcase. Probably not, but smell the oil on the dipstick to be sure it does not smell like gas.

BTW with the pump output line into an open container, it ought to pump out a pint or more in about 45-60 seconds at cranking speeds. Most can do this and more.

Either way, replace the pump. It could be a faulty pump. Also, you could have crud in the fuel tank that was sucked into the pump and is mucking up the inlet and outlet valves. You might want to put a clear filter inline before the pump for a while and see if it accumulates some crud; if you do have crud in the tank, it may clog this filter but at least you won't mess up the new pump.

Blow by mouth back into the main line to the tank with the gas cap off. It wil have some resistance, but you ought to be able to blow back into the tank. A lot of back pressure indicates the sock is plugging up and you have crud in the tank. Nothing to do at that point except pull the ank and inspect and clean and replace/recoat inside if you find a rust.
 
i asked my friend this same question, but wondering if it would be prudent to add check valves into the line itself? that way if the valves fail on the pump, i'll at least have a backup (you know the quality of auto parts these days). say, one before the pump, one after. or is that overkill?
 
also i took off the cap and blew into the line. sure enough, the fuel blew right past the fuel pump and back down the line. it wasn't even super hard to blow either.
 
mattmatthew said:
also i took off the cap and blew into the line. sure enough, the fuel blew right past the fuel pump and back down the line. it wasn't even super hard to blow either.
Click to expand...
Wow that IS bad. I meant for you to blow back into the line leading INTO the pump but you went further.

Your fuel tank sock could be off of the fuel pickup and you may still be drwaing crud in from the tank so keep that in mind. Look carefully into the pump and lines when you take it off.

No, don't put check valves in the lines. Just another part(s) to fail or cause problems. Let the fule pump valves do it. They are normally very reliable.

I just was helping a guy who had a bad Airtex fuel pump and so maybe they have a batch of bad pumps out there. His outlet valve was bad, as evidenced by an immediate drop in fuel pressure to the carb when he shut the engine off. (But he also found a a batch of crud in the pump so it might have been self inflcited.) Perhaps take it back to NAPA, let them know your problem, get your money back, and get one eleswhere that is not an Airtex. NAPA stuff is normally OK, but they don't make the pumps...... I just don't know what is better or worse. Maybe others can share info on that.

BTW, what year/model of car/truck?
 
it's a 1965 plymouth valiant, 225.

and i believe it's a pump manufactured by carter for napa. model M60577. label says made in the USA, but these days that usually means assembled by some dude in the USA with parts made in China and god knows where else.
 
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