Stranded… could use some ideas.

[Grit dog]

Repeat that with the gas cap removed.

Good call although it seems rather quick for the tank to develop a vacuum. Although if the tank was full it would happen much quicker.

one step further, make it die again and remove gas cap immediately. You’ll hear if the tank is not venting.

 

[Grit dog]

Nope, my blazer has a length of submerged hose inside the tank, towards the sender.

Here is the problem in my Blazer.

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Your blazer is also a TBI with pump in tank. OPs is not. Is there fuel hose in your ‘77 tank?

There is not unless someone Jerry rigged the pickup.

 

[Buickspec6231]

I know its completely different, by my GF's motorcycle had similar symptoms. The gas tank wasn't venting properly. It would run fine until a load was put on it or you rode for a while and then stall. Once it stalled it wouldn't restart for a while, or until you opened the gas cap to check to make sure you weren't empty. Then all of a sudden it would start. 10 minutes of work and a little rubber flapper removed and the bike ran fine again. As suggested by others I'd replace the rubber hoses and leave the gas cap off or loose. It could be why it runs fine off of a 5 gallon can with just a hose shoved in it.

 

[7900_Blazer]

So quick update. Thought we had it fixed, found a section of rubber hose not replaced.., the ends were dry-rotted. Replaced it and initially it seemed to run fine, then after about 3 or 4 miles, it again died in the middle of the street. Rehooked up the gas can in the floorboard and was able to get it back to my brother-in-laws house (son had to fly to Seattle for work).

I pressed it pretty hard using the gas can in the floorboard, but it responded fine, drove probably 25 miles total with the gas can in the floorboard.

Next thing I’m going to do is run rubber fuel line along side the steel line to remove it from the equation.

So far I’ve:
- dropped the tank and inspected the inside of the tank and pickup tube, all ‘looked good’
- added an electric fuel pump but it made no difference so got rid of it and went back to the standard mechanical fuel pump
- replaced various sections of rubber fuel line from tank to fuel pump)
- replaced the carb with one I just had rebuilt by Jett Performance in California (ran fine though with both with gas can in the floorboard)
- replaced fuel pump (runs fine with the gas can)
- removed the fuel filter all together (runs fine with gas can)
- loosened gas cap, runs fine either way with gas can in floorboard)
- once it cools down I’m going to run new fuel line (rubber) from tank to pump.

 

[AKguy]

Sounds like you have the issue surrounded!

 

[Corvette Ed]

This has been an interesting read. Good luck,keep us posted.

 

[Rusty Nail]

Question, is the sending unit inside the tank a solid line? Is there anything inside it that could wear out and collapse or is it a simple solid tube with a sock on it?

Also, the sock on the end of the pickup tube is a mesh right? Seems impossible for it to somehow seal up enough to stop up the whole line???

Just seems like this shouldn’t be brain surgery to get gas from the tank to the carb… crazy frustrating.

I thought you dropped the tank and looked at it because you reported that you dropped the tank and looked at it.

See where I got that idea?

Pretty interesting… after dropping the tank and confirming all is pristine inside the tank, replaced all the rubber hoses and pressurized the line; held pressure as it should.

I hold much doubt regarding the validity of this test and surmise you simply forced the plug in the line tighter if this ever happened IRL.
No need to run a piece of rubber hose along side the tube steel metal line, it hasnt failed. It may be crushed or pinched but until you blow air through both ends you'll never get the junk out of the line. Too bad youve had so much trouble but im not convinced it wasnt necessary. -There is an entire audience here reading.

Hi Mom!

 

[7900_Blazer]

Well I ran a whole new gas line from the tank to the pump and also again blew it out from the pump end. Tank is full so gas blew out everywhere.

It drove like it has up until Friday. There is a pretty steep hill, maybe 2 miles long, drove it hard up and back twice. The second time I kept it in Third and held it at about 3200 RPM… ran fine, so maybe that gets us back on the road.

I’m headed to Red River NM tomorrow, so I’ll keep you all posted. You guys (and girls) are great, so appreciated all your feed back.

 

[7900_Blazer]

So still stranded… thinking the new fuel line solved the issue, we took off for Red River NM, drove about 30 or so miles… died again on the side of the interstate.

Opened the hood, no fuel in the new glass fuel filter.

Took off the fuel hose at the carb… cranked it over… no fuel. Took off the hard line at the fuel pump, cranked it over, no fuel.

Took off the new supply line at the fuel pump (that connects directly to the tank), tried to blow through it, could not.
Took off the gas cap, tried again and I could blow through the line… ah… the tank isn’t venting says I…

Hooked everything back up, leaving the cap completely off. Cranked it over, takes it a bit to pull fuel from the tank, but after a bit, the glass fuel filter filled with gas, engine cranked up… Let it idle while I pack up my tools, drove about 10 yards, died again, opened the hood, again no fuel in the glass fuel filter…

Hooked the gas can back up in the floorboard, cranked and drove about 13 miles to a Love’s truck stop. Fill my gas can with 4.5 gallons of gas and drove back to my brother-in-law’s house without issue.

Runs great on the gas can in the floorboard, simply will not consistently run from the tank, even with the new supply line.

So, I’m thinking, the sending unit/tube has a vent of its own, maybe???? Maybe that vent is plugged, seems really odd that it won’t run with the cap off, which really only leaves the tube, getting stopped up…

Doesn’t really make sense that I could drive it around the block, seemingly run fine, and then die, change something drive it up the hill and back, and it run fine, drive it 30 miles, it dies again… but seems to run fine using the gas can in the floorboard.

Thoughts?

 

[7900_Blazer]

Quick summary:

- Drove for months around my home town to work and back and out to my ranch with no problems.
- Drove to Amarillo in the heat, then to Raton with no problems.
- Initially only ‘stumbled’ going up hills…. Ran fine on level ground and going down hills.
Then quit although.

- Has run fine on a gas can, 13 miles to Love’s then then 35 minutes + or so back
- It’s not the carb
- It’s not the fuel pump
- It’s not a vapor lock
- It’s not the fuel filter
- It’s not the fuel supply line

 

[Scott91370]

I don't think there is anything left to change.

This may not be possible but... What if you put the new fuel feed line directly into the tank, bypassing the sending unit? This would of course require the dropping of the tank again to remove it and open the top or removing the filler neck. If you did the from the last piece of hard line right into the tank you could eliminate the majority of the feed line.

Just a thought, may not be a good one but that's where I am right now.

 

[SquareRoot]

By chance, this engine doesn't have vortec heads does it? Asking for a friend. @Rusty Nail

 

[7900_Blazer]

By chance, this engine doesn't have vortec heads does it? Asking for a friend. @Rusty Nail

unknown…

 

[AKguy]

Time for a new sending unit?

 

[7900_Blazer]

Time for a new sending unit?

As far as gas flow goes, isn’t the sending unit just a pickup tube and a vent?