Having fuel delivery issues

[GMCGrim]

My second new fuel pump is not drawing fuel from the tank. The truck runs just fine pulling gas from a gas can on the floor. I bought the second new pump thinking the first one was bad.

So let's start from the beginning, new gas tank,new sending unit, new short pieces of 3/8 fuel line and rebuilt carb. I have read everything i could find on the subject of fuel pump problems. The lines to the pump are not plugged (I've
checked three times).

So now I am at the point of considering an electric pump or a high quality aftermarket mechanical from Summit or Jegs.

Oh by the way I have done all of this with the gas cap on and off and it doesn't seem to matter. Are the aftermarket pumps any better than the local parts store versions that cost 18-25 dollars.

[jakewalter]

If your truck runs fine from a gas can on the floor and you’re using a mechanical pump.
Do you have an inline filter? Some filters have a check valve. Could the filter be on backward? Have you checked the line from the sending unit to the pump for obstruction? Post a picture of the sending unit. I’m just shooting in the dark.
Jake

[GMCGrim]

Originally Posted by jakewalter

If your truck runs fine from a gas can on the floor and you’re using a mechanical pump.
Do you have an inline filter? Some filters have a check valve. Could the filter be on backward? Have you checked the line from the sending unit to the pump for obstruction? Post a picture of the sending unit. I’m just shooting in the dark.
Jake

No inline filter. The only filter is the one in the carb. The sending unit is in the tank and it is new and not plugged. The tank is also new and the lines to the pump are not plugged.

I am thinking that the pump does not have enough suction to pull the gas from the tank.

[hamjet]

If you remove the fuel line at the pump from the tank line it should run on the floor. if not, the problem is towards the tank..

[GMCGrim]

Originally Posted by hamjet

If you remove the fuel line at the pump from the tank line it should run on the floor. if not, the problem is towards the tank..

My lines from the tank to the pump are open without any obstructions. Everything in the system that is threaded has sealer on the threads so there no way for the pump to suck air and not gas. I am at my wits end with this. All I have left is a windshield and a front bumper then my project is finished.

[geezer#99]

Originally Posted by GMCGrim

My lines from the tank to the pump are open without any obstructions. Everything in the system that is threaded has sealer on the threads so there no way for the pump to suck air and not gas. I am at my wits end with this. All I have left is a windshield and a front bumper then my project is finished.

We assume the threaded connections are pipe thread and not flare fittings that are sealed.

[GMCGrim]

Originally Posted by geezer#99

We assume the threaded connections are pipe thread and not flare fittings that are sealed.

The connections are flare fittings but I put a dab of sealer on the threads that holds the flare in. At this point i am not leaving anything to chance as far as sucking air is concerned.

[geezer#99]

Originally Posted by GMCGrim

The connections are flare fittings but I put a dab of sealer on the threads that holds the flare in. At this point i am not leaving anything to chance as far as sucking air is concerned.

Any sealant of any kind on flare fitting threads can create a leak or a place for air to get in!

[midniteblues]

i had too "bleed" the fuel line on the kids truck.

disconnect the infeed line at the pump and direct it into a bucket.
then use a air gun/nozzle and your hand too seal it and blow air into the gas tank "slowly". fuel should start flowing out of the line at the pump.


is pretty crazy but this also works in reverse. blow the air into the disconnected fuel line at the pump. just be ready cause the gas will come out as soon as you let off the trigger.

either way reconnect at the fuel pump and give the engine a few cranks too see if your getting fuel through the carb yet but.....

after doing all this it still may be nessacary too disconnect the fuel line at the carb and crank the engine till gas comes out that line also. "although i never had too do this part."

[GMCGrim]

Originally Posted by midniteblues

i had too "bleed" the fuel line on the kids truck.

disconnect the infeed line at the pump and direct it into a bucket.
then use a air gun/nozzle and your hand too seal it and blow air into the gas tank "slowly". fuel should start flowing out of the line at the pump.


is pretty crazy but this also works in reverse. blow the air into the disconnected fuel line at the pump. just be ready cause the gas will come out as soon as you let off the trigger.

either way reconnect at the fuel pump and give the engine a few cranks too see if your getting fuel through the carb yet but.....

after doing all this it still may be nessacary too disconnect the fuel line at the carb and crank the engine till gas comes out that line also. "although i never had too do this part."

Thanks, that is probably the only thing i haven't tried yet. I always thought the fuel pump would have enough suction to pull the gas from the tank but I guess it is not so. I will keep at it.

[midniteblues]

Originally Posted by GMCGrim

Thanks, that is probably the only thing i haven't tried yet. I always thought the fuel pump would have enough suction to pull the gas from the tank but I guess it is not so. I will keep at it.

i always thought so too.
when i did the kids truck i had the same problem your having.
after cleaning the tank removeing the sock filter cleaning the sending unit tube and installed a new pump and lines still couldnt get any fuel too the pump no matter how long i cranked it.

i disconected the in feed at the pump too see what was up and it was dry after all that cranking
i thought perhaps some how its still clogged so i blew air into the dissconected line and guess what happened i got doused with gas

on my truck i did it into the gas tank even before trying too crank it over "just because i didnt need the issue again" just be carefull cause the tank can/will expand if you create a good seal.

i never had too do this on any other vehicles

[mike16]

I replaced my origonal pump after forty years of survice. lots of rust in the tank and aged rubber lines requires a complete fuel system r&r so as a precaution I replaced the pump too. the first replacement pump worked great for 8 months and then died, I think because it was pumping alot of rust and dibris. the next pump lasted less than two months and caused me problems with fuel pressure. defineitly debris related when I fount the carcass of a dead bee on the carb side of the exit fuel diaphagm. after finally getty the gas tank debris issue sorted out this third pump has lasted over 3 years.

another thing I discovered was that when you discover and resolve fuel problems like junk in the fuel systen dont presume the problem is solved. all that debris in the fuel system is still causing problems unless you go through and clean the entire system again. eventually the debris problem goes away but not without the expense of time , fuel filters and alot of embarrassing down time in busy intersections during rush hour.

dont put high pressure air from the fuel tank to the carb. it will blow out gaskets in your carb and may collapse your floats

for all the time it takes to inspect your fuel system its takes very little additional time and effort to actualy replace all the lines you are inspectin.

if you have rust and debris in the tank, it is better and cheaper to just replace the tank and float system together once and for all

[midniteblues]

awesome... i'm happy it worked for ya