fuel starvation, summertime edition-SOLVED 4 years later

[hooter]

8/1977 FJ40 cali spec fully smogged rig with charcoal canister, egr, ABV etc. (see avatar pic). As original as they come,freshened up a couple years ago.
new OEM gas tank,
new see through filter,
reflective tape wrapped hardlines,
rebuilt carb.
new rubber lines from tank to pump (i dont thing there is crap in the lines or the carb

I have no issues with the truck on my 8-15 minute commute.

I took the truck 440 miles this weekend to the coast. Yee haw, my furthest trip. 90 degress outside and a headwind of 15 MPH. i cruised at 60 where is seemed comfortable (33 in tires)

100 miles in, the truck falls on its face. I stop at a light and I shift through first, second, third fine. But on the transition to 4th back into the cruising speed, she falls flat sputtering bucking, kicking, etc. -fuel starvation. I have an empty bowl after immediate shut off and coast, half-full bowl after a moment of idle in the sight glass.

I changed fuel filter, no help
there is no whoosh out of tank when opened,
I cracked the gas cap for vent, no help.

I carried a spare gas can and i decide to fill the fuel tank to the brim. (6 gals the first time) Immediately, all symptoms resolve and she runs like a top......For 3 gallons and it does the same exact thing every 3 gallons of fuel used (45 miles or so). When the tank is filled to the brim, its a galloping jessie. After 3 gallons are used, its nonfunctional from starvation.



To me, it seems there is a vapor locked type scenario where the pump is not able to pull enough fuel out of a less than full tank. When there is a full pressure head, it works great. But when the fuel dips below full, it cant go above 30 mph.

So.....my question.
why can i run fine with a full fuel tank , but when the top of the tank is used, its starving every 45 miles?


thanks for the help
hOOter

 

[Cleg]

Impressive amount of info supplied above.

Just tossing this out as a guess.
"New fuel tank", My tank has (I think) 4 separate connections for the emission control system.
Is it possible that your fuel pump is connected to a line that does not go to the bottom of the tank?

Alternately could the fuel pickup is somehow perforated and allowing air into the line when you get a few gallons below full?

I suppose you could check all of that without pulling out the seat and tank by setting up a siphon to the fuel line in front of the fuel pump to drain the contents of the gas tank into gas cans.

Good Luck.

Cleg

 

[hooter]

Thanks for checking and replying.

When I’m daily driving. I can run the tank to near empty with no problems. The pick-up seems to work fine, as long as it’s not on a continuous run.

 

[POTATO LAUNCHER]

My V8 40 does the same thing on extended runs ( few hours on the same tank) but only above 95° heat. What I have deduced is like you said, vaporlock. Wooden clothes pins on the hard line act like a heat sink and will help some. The problem is the ethanol content in modern fuel. Boiling point is much lower and it's near impossible to find pure fuel while on the road. If I top the tank off it will be fine until about half tank. At that point it does exactly the same as yours. A phenolic carb insulator and heat shields and a hand full of clothers pins on the line do help but I have yet to find a way around the fuel. Additives and octane boosters have no effect either.
It was a common topic last year at SAS. Many carburated Cruisers had this very issue. If someone has a solution it would be greatly appreciated.

 

[hooter]

Wow.
This really isn’t the news I want to hear.

I was hoping for ‘eliminate your widget’ or ‘new fuel pump’ or or or.

I want to take some long range trips but it seems impossible with modern fuels in old ‘keep em original’ vehicles


Hooter

 

[hooter]

is this a case where an electric fuel pump would improve a situation?

 

[rkymtnflyfisher]

My rig runs great in hot weather, any distance I drive.

Sounds like you're building a vacuum somewhere in the fuel system ahead of the carb.

The tank is suspect to me, the woosh that you mentioned make me think that.



Edit-I misread the woosh part.

 

[rkymtnflyfisher]

is this a case where an electric fuel pump would improve a situation?

@Solace in Solitude may have some good insight to this question.

 

[rkymtnflyfisher]

New rubber lines from tank to carb.


Any chance that line is getting soft and collapsing?

 

[Steamer]

You could always disconnect the hose at the fuel pump and put on a temporary electric pump and pump the tank into some fuel cans. That would show if the pickup tube and hose are functioning properly. If you have enough height you could even siphon it out.
Maybe the fuel pump is just weak?

 

[ToyotaMatt]

Hey Hooter ,

im gonna take A Wild Card Shot & say Maybe this is Partially Electrical in some way ?

- U have all the symptoms of a Bad Fuel Cut Selinoid

- or the B+ Signal going to it is getting interrupted some how ?

- Or

u have a Bad Igniter for example , with a on / off signal maybe


this would explain why the bowl goes dry perhaps


ok, so Its Outside The box Concept

but so is all your symptoms



good luck ,

PM me if u u need anything , i will help in any way i can ........................

 

[POTATO LAUNCHER]

I was thinking the same with an electric pump. Heat is the common cause of this and it varies from fuel stops. I do notice that the cooler fuel coming from the ground into the tank has immediate results.
I never had any issues years ago in the same cruiser with the exact same fuel delivery.
Fall trips or winter trips there is no issue.
Only when the ambient temps are high and continuous running highway speeds is there a hesitation.
It's not just a 40 or Cruiser thing either. My classic and muscle car friends say the same thing.

 

[samatulich]

Maybe it has to do with the vacuum lines or the secondary?

 

[hooter]

New rubber lines from tank to carb.


Any chance that line is getting soft and collapsing?

This crossed my mind. But what confuses me is the full fuel tank runs great and 3 gallons later it’s dead. The temptation is to change a bunch of stuff but then I’ll never know what actually works.

 

[lcwizard]

@hooter
Common in Az. You need to keep the fuel cool in the lines. A high volume electric with a regulator that has a return built in will work.
Put the regulator on the firewall as close to the carb as possible. I've used the Walbro injection pumps. They flow a lot more fuel than you need. The return will keep the fuel cool as it's always circulating back to the tank.
Adding the gas to the tank introduced a cooler mix, solving the vapor lock.
The Walbro is a frame mount, put it close to the tank. I reroute the fuel lines up the firewall to the regulator on the carb side behind
the air cleaner, on the firewall, keeping the feed line as short as possible . You'll be able to feel the difference in the fuel temp with your hand on the line vs stock
Stock, the return is too far downstream from the carb. The vapor lock occurs between the stock fuel pump and carb where it passes
a couple feet of hot engine. I would bet you have no issues in the winter.

 

[hooter]

I would bet you have no issues in the winter.

you are correct sir. ive never had an issue with it in the winter.


is ethanol free a temporary solution or is the modern fuel mix still an issue with vaporization regardless of ethanol?

 

[ToyotaMatt]

you are correct sir. ive never had an issue with it in the winter.


is ethanol free a temporary solution or is the modern fuel mix still an issue with vaporization regardless of ethanol?

- u have a Suction line on bottom of tank

- the return is mid way up on side

- what if the supply and return got swapped some how by a PO ........?

 

[ToyotaMatt]

 

[hooter]

Lines are plumbed correctly

 

[GA Architect]

I keep this app on my phone and check the route before I take a long haul with my rig: Pure Gas