vent line for fuel tank plugged?

[1972BackInBlackC10]

was wondering if the vent line on my truck was plugged if it would cause the truck to die? seems like its losing power and if try to feather the gas pedal or floor it the truck will die either way even if yu just take your foot off the gas, the truck starts fine and runs fine but a soon as you get a certain distance it does this, iv basically replaced everthing there is that could cause this problem nd im about to put in a new fuel tank does anyone think it could be a plugged vent line or possibly mixed up return and feed lines as my friend elimnated the second fuel tank nd possibly hooked them up wrong

[SS Tim]

Just loosen the fuel cap and test drive it. If the system is not venting it would drive similar to what you are describing.
What was the aux tank like? Was it the factory NL2 on the SPID?

[wilkin250r]

Sure sounds fuel related, doesn't it?

Try running with the gas cap off, provided your tank isn't so full it will slosh out. That's a quick, easy method of determining that problem.

How long before it dies? You're not pulling THAT much fuel, I would estimate it would take half an hour or more of steady driving to drop enough pressure in the tank to cause the engine to die. If it's significantly faster than that, I would say your problem is somewhere in the fuel line.

I had a similar problem with a 72, and it turned out to be a kinked fuel line. If the truck sat for hours, enough fuel would leak past the kink to fill up the fuel line, so it started just fine. However, it only took a couple minutes to drain the fuel out of the line, then the truck would die because it couldn't pull any more past the kink.

I finally diagnosed the problem by hooking up a small, inline fuel pressure gauge right before the carb, and I saw the fuel pressure drop, and then found the cause. Have you hooked up a fuel pressure gauge and determined that it truly is fuel-related?

[1972BackInBlackC10]

so if i take the cap off it should drive fine? im not sure whats on the spid the other tank is no good, its an 80 gmc did i post this in the wrong forum?

[1972BackInBlackC10]

nevermind i osted it in the right place lol blonde moment, and it does it right away i get like 2 blocks away and it wants to die, the ling from the pump to carb isnt kinked, so im wondering if maybe my friend mixed up lines when he by passed the second tnk maybe?

[SS Tim]

No, I'm in the wrong model range. How did I get to a square body issue? Oh well. Try the cap but if it is dying that soon it sounds more like a plumbing issue. Check a factory schematic.

[1972BackInBlackC10]

im assuming then its either crossed lines, or my sending unit in the tank maybe, once it does it will start again but as soon as you put it in gear and start driving it pretty much does it again, like i said iv replaced everything but tank, sending unit, fuel lines, i will check the fuel and vent lines, and no clue how you ended up on the square body tim lol

[donut]

Do you have fuel flow? Double check all of your lines, but don't rule out the pump heading south.

[1972BackInBlackC10]

i put a brand new pump on, i think i fund my problem, i crawled under the truck and all my lines are good they arent kinked, but my vent liine has been cut down to 2 inches long and has a bolt shoved in the end of it, i think my friend must have thought it was a carry over fuel line from the second tank and plugged it off, i need to get some line to extend it when i drop the tank to change it and hopefully thats why its been dieing, im thinking thats what it is because on cooler days you can drive it further

[1972BackInBlackC10]

now i just need to figure out how to get the gas tank straps off

[wilkin250r]

You shouldn't need to undo the actual straps themselves, just unbolt the whole thing from the frame rail and drop the tank with straps intact.

Clear the vent line, obviously, but did you ever try running without the gas cap? It's your time and money, but personally I would suggest nailing it down definitively before you go chasing problems. As I said earlier, I diagnosed mine with a small inline pressure gauge, I think I picked up mine for $7.

When I found the fuel pressure drop, I took another $4 in fuel line and hooked the fuel pump pickup line to a gas can right beside me rather than the fuel tank, and that verified the fuel pump was good because it ran perfect.

I'm not trying to insult you, believe me, just trying to help. You've already replaced a fuel pump, probably fuel lines, and whatever else. I think a lot of that could have been avoided if you had spent a little more time on your diagnostics, and I would hate to see you keep making that mistake. There's a possibility this whole issue is heat and spark related, and not fuel. I'd just like to see you nail it down definitively before you go replacing more components.

[1972BackInBlackC10]

no worries m not insulted i should have spent more time on diagnostics, i looked at my tank and someone stuck a bolt in the end of the vent line, who knows that might not even be the problem, and i did find out about the brackets like you mentioned and will be changing the tank regardless because i already bought a new one and i cant return it because i sprayed t with undercoatng and while its out i will change the fuel lines

i guess on the bright side i wont have to replace anything for awhile since i put in all brand new dist cap, rotor, ignition module, took out dist cleaned and checked vac advance and spring weights, solonoid, plugs and wires, carburator, filters, battery, alternator, fuel pump

[jhngardner367]

If it had dual tanks,it could be a faulty switching valve. That's what was causing mine.I by-passed the valve,and no more troubles(I'm only running 1 tank,now).

[WarBeard]

One of my first cars had a bunch of crap floating around in the tank. When I would start it up the suction screen in the tank would clog, the car would die all the stuff would let loose of the screen. I could start it back up and as soon as the screen clogged it would die.

[1972BackInBlackC10]

yea i pulled my tank out, took the sending unit out and its all rusted up, i dumped a lil gas out and it was brown, so im thinking i und my problem