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

[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..

[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

[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.

[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.

[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 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.

[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.

[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]

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

[GMCGrim]

Originally Posted by midniteblues

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

Thanks, Midniteblues I will blow some air into the tank sometime this week
and see what happens.I hope that will put an end to this and the truck will stay running. Like I said earlier I was at the point of going with an electric pump.

[SonnyBoy]

I'am having many of the same issues with my 68 ( stepside )
I just got it on the road in July and working out the little bugs you always have with a new motor. Everything works great except for intermittent fuel problem. I have a new Jegs mechanical fuel pump 110gph . Fresh 454 just back from Cope Bros.Racing . Curious to here how you get your fuel issues resolved .
I have replaced everything but the tank. ( New vented Stant locking cap,sending unit, 3/8 aluminum fuel line from tank to fuel pump.all new 3/8 rubber hoses. )
I had one of those Mr.Gasket clear view in line filters, it worked great. I couldn't see much in the way of debris . I did notice bubbles would appear in the filter every so often . I talked to some of the local speed shop guys about the bubbles, they said it was normal to see a little of that. I have just replaced the Mr.Gasket clear view in line with a billet alum. Edelbrock in line . I was told by the local Total Performance shop the glass filters cost him a fire ... not worth the risk.
Before firing it up I filled the tank with New Gas ( 92 octane ). I have only run about 4-5 gallons thru the new motor , have been ramp trucked home once .
Embarrassing !!
I am going to install another fuel pump tomorrow. This time just a stock Big Block factory fuel pump and see if its not the Jegs Pump. I talked to one of the local mechanics and his buddy had a problem with his Jegs pump on his boat , they replaced it with another Jegs and it was a bad pump .. Who knows .

[clemsonteg]

Originally Posted by SonnyBoy

I'am having many of the same issues with my 68 ( stepside )
I just got it on the road in July and working out the little bugs you always have with a new motor. Everything works great except for intermittent fuel problem. I have a new Jegs mechanical fuel pump 110gph . Fresh 454 just back from Cope Bros.Racing . Curious to here how you get your fuel issues resolved .
I have replaced everything but the tank. ( New vented Stant locking cap,sending unit, 3/8 aluminum fuel line from tank to fuel pump.all new 3/8 rubber hoses. )
I had one of those Mr.Gasket clear view in line filters, it worked great. I couldn't see much in the way of debris . I did notice bubbles would appear in the filter every so often . I talked to some of the local speed shop guys about the bubbles, they said it was normal to see a little of that. I have just replaced the Mr.Gasket clear view in line with a billet alum. Edelbrock in line . I was told by the local Total Performance shop the glass filters cost him a fire ... not worth the risk.
Before firing it up I filled the tank with New Gas ( 92 octane ). I have only run about 4-5 gallons thru the new motor , have been ramp trucked home once .
Embarrassing !!
I am going to install another fuel pump tomorrow. This time just a stock Big Block factory fuel pump and see if its not the Jegs Pump. I talked to one of the local mechanics and his buddy had a problem with his Jegs pump on his boat , they replaced it with another Jegs and it was a bad pump .. Who knows .

I would think bubbles in the filter before the pump would indicate an air leak. Have you checked all your connections to make sure it isn't pulling air somewhere?

[SonnyBoy]

I have my in - line filter after the fuel pump and before the carb.
I really wondered why you would see any bubbles at all. It doesn't like, blow bubbles or anything like that . It just has a bubble in there after you start it, then it dissipates to a very small bubble while running. After it has " acted up " and I'am sitting on the shoulder of the road, I have popped the hood and found the old Clear View filter was EMPTY . It may be the fuel pump. Seems unlikely to me,
after it has " acted up ". sometimes it will have a shot or two of gas get thru , just enough to give you hope that it healed itself only to shut down again. After it sits awhile it will have gas reappear in the filter and start again. I thought it may be "vapor lock", but it didn't have any issues like this before . I haven't changed any of the fuel line routing . Puzzling .
I have noticed, when I still had the Mr.Gasket clear view in-line filter installed, the fuel filter would be full when shut off or nearly full with maybe a small air bubble in view. I would check it in the morning and sometimes it would be full ,
other times you could actually see it emptying back into the fuel pump.
I'll throw a new stock pump on in the morning and see if that was it , keep you posted.

[GMCGrim]

Originally Posted by clemsonteg

I would think bubbles in the filter before the pump would indicate an air leak. Have you checked all your connections to make sure it isn't pulling air somewhere?

I think I got everything worked out today. I blew air into the gas tank while holding my hand over the opening. The line that feeds the fuel pump was disconnected. When gas started pouring out I reconnected the line to the pump
and bingo withe air out the line I was in business.

I even took a trip around the block to see how it would run and everything seems to be ok now. I even let it sit for a few hours to see if it would restart without putting some gas in the carb and it started right up.

I will have say these trucks are a special breed, I have never had to do this with any other vehicle i have owned. Thanks Midniteblues for the tip about blowing air into the tank. I would also like to thank everyone who responded
to my post.

[midniteblues]

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