Howdy y'all...interesting problem here. I'm pretty sure this is a somewhat common problem, but unfortunately the search does not seem to return anything, so I do apologize. I can't add more than half a gallon without the pump shutting off. If I try to hold the trigger steady very lightly, it sprays everywhere after half a gallon (as expected given this condition). I've tried three different gas stations and I know it's the truck. This started today, with no previous symptoms. My gas gauge is not functional, but based on my last fillup and the miles driven since then, I should have been at approximately half a tank (I keep a notepad). This is a '79 with a single rear 19-gallon tank.

I pulled off the filler and vent hose to inspect everything. Everything is clear inside. There isn't a single obstruction in the metal filler and vent tubes on the bed, or the rubber hoses attached to the tank. As far as I can tell, there is no obstruction anywhere from the gas cap down into the tank, and back out through the vent. I can stick a coat hanger down there no problem. The hoses are a little old, but don't seem collapsed. The small metal door that the pump nozzle pushes open works fine. The only other symptom I can really identify is that there seems to be a burping sound as it tries to fill up, which makes me suspect the vent hose but I can't find anything wrong with it.

I'm really stumped here as I can't find a problem after a thorough inspection, so I'm throwing myself at the mercy of the truck gods. Since this seems to be a common problem, does anyone have any suggestions?

 

That IS an interesting one! Certainly sounds like it's not venting. Never had this happen myself. Have you tried putting air down the vent line to see if it comes out the filler. Or the other way around? That would prove the vent line clear or not, without getting gas everywhere. Can't think of anything else. Came on suddenly huh? wierd. (you're certain the tank isn't full, Right?)

 

It sounds like you are on the right track. Maybe if you disconnect the vent hose at the tank and see if it will fill up. My wifes 05 mustang does this constantly. I have to do foreplay to get it to swallow. Wish I could help more.

 

Is your vent hose taped to the filler hose? I had a problem somewhat similiar but not as bad as you are describing. Someone suggested taping the hoses and it seemed to help.

 

Some of these trucks did this when they were brand new as well. I was a gas pump jockey when these trucks were new. On some of them you had to twist the pump handle almost upside down to keep it from shutting itself off. You couldn't pull the handle out too far or it would shut off because of the evap emissions sleeve over the nozzle. I realize your 79 has a gas door, but you might try twisting the nozzle around right and left to see if it helps. Sorry I don't have the magic answer for you.

 

Guys, thanks so much for the helpful tips. While I am confident that the tank was not full at the time, I have to agree that it does sound like a venting issue. Sean - I really like your idea about taping the hoses together. They are supposed to be like this from the factory, yet my tape is dangling and the hoses are no longer held together. I will try this tomorrow.

My current plan is to drive it for a little while longer and try one more time this week. I will see if rotating the handle has any effect on mine. If the problem persists, I will drop the tank and inspect the inside with a flashlight. I need to replace the sending unit anyway. At that time I will install a new filler hose set as preventative maintanence.

Thanks again guys; I'll post back the results.
Jeff

 

I'm curious about the " taping the hoses together " thing. How does this help? By keeping them together so that they support each other and don't flatten out? Or...?

 

Fmc, here...everything you need to know about solving that pesky issue.

Inspect all the emissions components. One reasons why I don't like '79s, most trucks had the FULL emissions package. More stuff to break.

1) Make sure the gas cap is pressurized type, not vented.

2) 90% of the evap. lines are steel fastened on the passenger side of the frame rail. Inspect to make sure nothing has rusted, kinked, or developed a hole or two.

3) Make sure the evap. canister is functional & free flowing.

4) Inspect all rubber hoses of the emissions system.

5) Pour some gas down the filler neck with a gas can, then immediately look down to the filler/vent hoses. What you can't see doesn't mean it's good.

The vent hose must be taped to the main filler hose like white on rice otherwise you will have issues filling it up. There are two places where it's supposed to be taped; one right before the frame, one right after the frame. Friction tape does a good job.

I never had issues filling up all of my dentsides. This stupid little filler hose/vent thing really make or break the filling experience.

P.S. if you need to replace the filler hoses, fix the nonfunctional gauge at the same time!

 

I just replaced the tank (midship), and sending unit in my 77f150. The old filler hoses looked ok, but I put new ones on and it came with the metal bracked that keeps the large hose from rubbing, or going closed, or getting piched as it comes up over the frame. I know you said your tank is in the rear, so I am guessing it would come up over , or near the frame as well.
I guess I am just thinking the large hose is kinked on the bottom, and the gas is not going through as fast as it is coming out of the nozzel, and backing up and shutting the nozzel off.
Starting all of a sudden seems real odd. I got my stuff from Bronco graveyard, who had good prices, and they were real decent to deal with.
Wish I had a better answer for you I know you helped me out tremendously in the past, but I am just thinking out loud. Please let us know how you make out and good luck!!

 

It helps with the venting in proximity is my suspicion. This issue is more prominent on trucks with the full ECP because the tank has no way to vent other than the charcoal canister and the EGR.

 

I don't want to hijack, but my 76 does a similar thing, only I think it is because of the cap on the outside, my dads old 73 did the same as well. Only thing is his truck always did it unless you turn the filler nozzle upside down, mine some gas pumps do work normally while others I have to turn it upside down. His truck was mostly original, but mine isn't, I don't have any emissions stuff on mine anymore, no carbon canisiter, no egr, nothing. Me and my dad, always assumed it was the newer style fuel pumps, having to turn to upside down and taking awhile to fill up the tank slowly is a pain. I'm hoping when I put my 79 bed on there it will make life easier. Other than checking the vent, is there anything else I can do to make it a little better for now until I do the bed swap?

 

It doesn't matter. I never have problems with any fuel pumps, old or new. If the tank(s) isn't venting properly, you will have issues.

I know how they work inside/out, and I never had to do anything (turning the nozzle, go slower, jiggle, etc) to make it go better. I go full blast and it always gulps it down like a hobo and a $6 bottle of whiskey. I fill up at any and all stations without issues, both with the nozzle restrictors and without. Whenever I get a dentside I check the filler hose/vents along with giving the truck a complete tune-up.

 

When you bought a new fuel filler hose at the parts counter, the vent hose came with it and was taped to the fill hose in three places.

If the vent hose isn't taped, it can collapse, making these slow fill fuel tanks...a no fill fuel tank.

You also want to make sure the replacement vent hose is the correct length. If it's too long, it can collapse...taped or not.

btw: The 1973/79 Styleside inside the frame mounted fuel tanks have been notorious since day one for being a slow fill.

 

I have yet to try mine, the new tank is setting there without a drop of gas in it yet, I am still working on the engine. I hope I am flowing nice when the time comes!!

 

Anybody got pix of the tape and locations? I'm having the same issue.