Stranded… could use some ideas.

[AKguy]

And return line, if equipped.

 

[Grit dog]

Bummer, man. Seems like you're sucking up some varnish on the screen in the tank, that may go away when not pulling fuel through it. I know you said everything is clean when you dropped the tank, but then alluded to not having dropped the tank and not pulled the pickup/sender out.
Not that it's fixed, but at least it sounds like you've isolated the issue!

 

[Zoomalot]

Had basically same issue on "87" Twin Tanks.
When I pulled the tanks off and apart the "E" fuels had basically disintegrated every rubber or plastic part
in the fuel system "serious" mush!! That included tank switches also.
I replaced the entire fuel feed system!!!!!!!!!
Problem solved

 

[Bextreme04]

I agree, the only thing you haven't ruled out is the sending unit. They are cheap, I would drop the tank and replace the sending unit. Clean the tank out really well while you are at it. If you don't have a return line, it will be a three port model. 1 Feed, 1 Filler vent, 1 Tank vent. It is HIGHLY unlikely that you have a plugged tank. It is much more likely that the pickup is getting clogged.

 

[SquareRoot]

Had basically same issue on "87" Twin Tanks.
When I pulled the tanks off and apart the "E" fuels had basically disintegrated every rubber or plastic part
in the fuel system "serious" mush!! That included tank switches also.
I replaced the entire fuel feed system!!!!!!!!!
Problem solved

Apart from avoiding "E" fuels what says this won't happen with your new fuel system?

 

[Bextreme04]

Apart from avoiding "E" fuels what says this won't happen with your new fuel system?

Almost all modern fuel line you can buy in the US is rated for ethanol now. If the old fuel line was installed more than 10 years ago, it might not have been rated for E fuel and if it was installed 20 years or more it definitely was not rated for it. Even with rated fuel line, it will still eventually rot out but much slower. You can probably get another 10-20 years from it first.

 

[SquareRoot]

I was more interested in the "plastic" parts he mentioned. Just wondering if the plastic on the sending unit actually turned to "mush" as stated?

 

[7900_Blazer]

So an update, still stranded.

I dropped the tank a second time… the sending unit is simply a tube with a sock on the end… , nothing there to block anything.I did go ahead and remove the sock though just to be sure.

There are no vent restrictions… all clean.

The last time it died, I was headed down hill, I had disconnected the feed line from the tank and gas would gravity-flow out… so there are no restrictions from the tank to the fuel pump.

When there is hardly any fuel in the fuel filter, I can take the fuel line off at the carb, and there is pressure in the line.

Question, how does fuel vapor lock inside the fuel pump?

I simply cannot get consistent fuel flow to the carb. It will idle (most of the time) on what little fuel it is getting… but not enough to feed it under load, like going up a hill…

Anyone ever bought a new, bad fuel pump?

How do you solve vapor lock issues? This thing has been running for 46 years.. so I don’t understand how all of a sudden fuel is vapor locking in the pump…????

 

[SquareRoot]

Defective "new" parts are rather common with the junk that we get from offshore vendors. It's very possible you have a defective fuel pump.

At this point, I would bite the bullet and try another new pump. The diaphragm inside may have an "intermittent" leak that's only noticeable under load. Stranger things have happened.

What has changed. Your now at altitude...correct? Air pressure.


Also, are you sure that there's no joints or fittings in the fuel line that are suspect? Extra, hidden fuel filters? Fuel lines getting hot due to nearby exhaust?

 

[SquareRoot]

Check that glass filter. It's possible the O-rings are leaking enough to be sucking air. I still think your "new" pump is pushing air into the line. Under load, I think its causing the pump to lose its prime.

 

[Itali83]

I’ve had pick up tubes in my big rigs crack and will suck air before fuel. Most crack at the top so they just suck air. But I’ve had one crack half way
Down so full tank it ran fine, half tank nope. Just an idea.
I big on diagnosing problems and not just throwing parts. But at this point, you gotta start throwing some parts at this thing to get you home. I’d do a new pickup just because.

just another thought. A fuel pump don’t care what the load is on the engine. It just moves fuel. Also, I may have read over it, but is this a return style mechanical pump or no?

Ben

 

[SirRobyn0]

I dropped the tank a second time… the sending unit is simply a tube with a sock on the end… , nothing there to block anything.I did go ahead and remove the sock though just to be sure.

Question, how does fuel vapor lock inside the fuel pump?

I simply cannot get consistent fuel flow to the carb. It will idle (most of the time) on what little fuel it is getting… but not enough to feed it under load, like going up a hill…

Anyone ever bought a new, bad fuel pump?

How do you solve vapor lock issues? This thing has been running for 46 years.. so I don’t understand how all of a sudden fuel is vapor locking in the pump…????

First don't run without the sock long term. It's there for a reason to keep junk from getting into the line and getting up to the fuel pump where it'll hurt the fuel pump.

Vapor lock is caused by heat. Getting enough heat into the fuel pump or line before the pump to cause the gas to boil. Again if this is happening your fuel filter will be very hot. If it's got headers it's more likely to happen. If it happens after only a few minutes of operation it's not vapor locking.

Whatever happened to adding a pusher pump to get you by for now?

Check that glass filter. It's possible the O-rings are leaking enough to be sucking air. I still think your "new" pump is pushing air into the line. Under load, I think its causing the pump to lose its prime.

I assumed that the fuel filter is between the pump and carb where there is pressure not suction.

If you truly have cleared everything else then what's the harm in trying another pump.

Did you ever check to see if the cam lobe might be wiped? I'm still not convinced that's it but you have eliminated so much already.

 

[Bextreme04]

Again, sending units are fairly cheap. If I was going through the trouble of dropping the tank, I would have replaced it at that time, just so I would know I didn't need to drop it again. The fact that you are getting the same issue with a brand new feed line and then couldn't blow air through the sending unit afterwards says you have an issue with the sending unit or something plugging it in the tank. Since two of the three tank vent locations are located in the sending unit also, I would have changed it based on your previous tank pressurization concerns also.

 

[SirRobyn0]

Again, sending units are fairly cheap. If I was going through the trouble of dropping the tank, I would have replaced it at that time, just so I would know I didn't need to drop it again. The fact that you are getting the same issue with a brand new feed line and then couldn't blow air through the sending unit afterwards says you have an issue with the sending unit or something plugging it in the tank. Since two of the three tank vent locations are located in the sending unit also, I would have changed it based on your previous tank pressurization concerns also.

I agree with this way of thinking as well.

I doubt, it's vapor locking which was really my point in my last post, but you had asked about it so wanted to give some info, and here is some more. If you really want to check that, next time it fails shoot the temp of the fuel pump, line before it and the filter with your IR temperature gun. Gasoline because of various additives that can vary from brand to brand and may be changed with the time of year or part of the country. But it does not have one single boiling point, and how much suction is going on in the line before the pump will effect it as well. The rule of thumb is if you get temps over 120F you are at least in the danger zone for vapor lock. Anything over 140F makes it pretty likely to occur, which is why I said put your hand on the filter to see if it is screaming hot. Also I don't think you have ever answered this question or I missed it, but if it has a return line, which you'd know because there are three lines on the pump those are pretty hard to vapor lock unless in extremely hot conditions. Vapor lock resistance is exactly why the return line systems were created.

 

[Camar068]

Time for a new sending unit?

agree....only thing I haven't seen changed. Sorry but after a few times getting stranded, I'd changed everything from the fitting at the carb back (pump, temporary rubber hose for line in a pinch, and the sender). Sorry 7900, being stranded stress's me out and I tend to throw the book at the damn thing lol.