My truck developed a very frustrating intermittent fuel problem today. This afternoon I hooked up to my boat and drove about 10 miles to the river without any problems. I left it idling while waiting in line to launch and after idling for about five minutes it suddenly started to stumble and then stalled. I cranked and cranked while pumping the accelerator to no avail, so I got out and pulled the lid on the air cleaner and flipped the throttle linkage a few times: no fuel. I had worn the battery down from cranking so I found an empty plastic water bottle, pulled the gas line off my boat, and pumped some gas into the bottle which I then poured into the bowl vent on the carburetor to fill it. After that it fired right up and stayed running for the remainder of the time while I was waiting in line and while I was busy launching my boat.

After a few hours out on the river I came back, jumped in the truck and it started right up. I backed the trailer into the water and left it idling while loading it, then parked it and shut it off for a few minutes while I secured everything. Started it up again and took off, drove about 1/2 mile and slowed down as I approached an intersection when it stalled again. This time I left it in third gear and coasted while pumping the accelerator pedal until I ran out of momentum but it failed to restart. So, once again I refilled the carb bowl, started it up, and drove 10 miles home without any issues at all. I met my neighbor on the way home and left it set idling for about five minutes while talking to him with no problems, then took off and drove another 1/4 mile. But as soon as I turned into my driveway it stalled again. This time after priming the carb I just left it parked and let it idle, but after about 30 seconds it stalled again. After repriming the carb a fourth time I took off immediately after it started and it continued running without a hiccup until I parked it in the shed and shut it off.

I have dual tanks with a universal three port electric switching valve and a stock mechanical fuel pump. Both tanks were filled on Friday so its not low on gas. The switching valve is wired so when there is power on the terminal it runs on the front tank. The first time it stalled I was using the front tank, but after that I switched to the rear one and the problem persisted. I doubt it was an issue of power loss to the valve since it defaults to the rear tank anyway when there is no power to the valve. I replaced all of the rubber lines last week because one of them started leaking, but I know all of the connections are tight. My best guess is a weak fuel pump since it only seems to happen when the engine is idling or running below 1500 RPM, at which point maybe its unable to keep up? I also find it strange that I was unable to roll start it before too, because I had turned the engine over at sufficient speed and given it enough time to reprime itself before I ran out of speed.

Thoughts? This has me very frustrated because it happens so randomly and intermittently.

 

Which truck is it? The 460's apparently had a problem with vapor lock, since Ford went to the trouble to put electric pumps with a return line and they also had mechanical pumps on those engines with return lines to the tanks.

Any exhaust modfications? If the exhaust is routed differently, it can put too much heat in the fuel lines if they are too close.

Those rubber lines; Are the fuel lines stock or are they rubber going all the way up front and not the stock routing?

 

Its the '84 F-250 with a 460. I've been running this truck for years with absolutely no problems up until today. It does have a dual exhaust system but its the same system I've had since restoring it and nothing was changed in the routing of the exhaust system prior to this problem developing. The rubber lines are just short pieces between the stock metal lines and the switching valve, sending units, fuel pump, and filter. Some are only a couple of inches long and there aren't any kinks in them. I never knew the reasoning for the electric pumps on some 460 trucks. My '86 snow plow truck is a factory 460 truck which was originally equipped with a mechanical pump that has never caused any problems. I believe that one does have a return line on it though, my '84 does not. But I've been driving it for 15 years that way and never had a problem up until now.

I'll have to recheck the rubber line going to the fuel pump. Because of the way the pump inlet is turned I had to make a small loop in the hose to avoid kinking it and it may be running closer to the exhaust manifold now than it was before. That's the only thing I can think of right now after you mentioned vapor lock. I've never experienced it before so I'm not sure if that sounds like what may be happening in my case? Would it be more likely to happen at slower engine speeds?

 

Another thing I just thought of...when I had the lid off the air cleaner with the engine idling I did notice a lot of fumes were visible coming out through the bowl vent.

 

Changed the fuel filter recently?

Might be a little water in the fuel you just got.

Two more possibilities.

 

Subscribing just to follow since I have the same mechanical pump.

Do you have any gasoline smell if you check your oil?

 

I had the exact same symptoms when a truck I built was vapor locking(a 53 f100). I put a 351c in it with headers and dual exhaust. I kept the original fuel line, it ran on the inside of the driver's side frame rail on up to the front.

When I would first start it, everything was fine, and driving down the road, everything was fine. I would get into town and it would start acting up and then finally stall. If I let it sit or get some gas in the carb it would run, and as long as I was moving it would be fine again.

I found out even though the fuel line was 5 or 6 inches from the exhaust header, the heat radiating from it was heating the line. As long as I was moving down the road, the airflow from moving would keep it cool enough. When I started stopping it would slowly heat the line up till the fuel started boiling. I put a clear fuel filter before the carb and I could let it sit in the driveway and watch it. It would take a long time just sitting there unless the engine was already warmed up, but I could see a bubble start in the filter. Then another, then another, till the fuel filter would be empty. It would run a minute or so more and then quit.

What I did to fix it was move the fuel line just a 1/4" on the outside of the frame rail. The frame shielded the fuel line and it didn't have any problems after that.

I also do not like some of the fuel line they sell now. To me they wrap it too tight on the roll and when they give it to you, it's not round it's oval.

 

Do you think reflective insulation would make an appreciable difference?

 

I was thinking of this myself. Franklin's advice makes a lot of sense and I'm pretty sure the problem is in the hose between the fuel pump and metal line on the frame. The inlet on my pump curves upward and the line is in the stock location directly below the pump on the crossmember. Because of the pump inlet I had to make a small loop in the line to avoid kinking it, and I'm willing to bet that loop is a little closer to the exhaust manifold now. I could put a 90 degree elbow in there, but I'm afraid that would just add more restriction and I'd rather avoid adding more fittings. I did some digging around in our junk vehicles at work this morning but I couldn't find a piece of that insulation. None of the parts stores here carry it either, so I'll have to see what I can find online.

 

I just ordered this stuff for the hose on the fuel pump:




Its claimed to reflect up to 90% of radiant heat so its worth a try. I'll have it in two days and I'll report back with the results as soon as I've driven it enough to know whether it was effective.

 

Success! The heat insulation arrived yesterday so I put it on last night after work. It has a velcro seam so you can wrap it around the line and stick it together, but I stuck the edges together first and slid it over the line like a tube. I only needed about 12" to cover the hose between the fuel pump and the steel line on the frame. Today I drove it to work...it was probably the hottest day so far this summer (upper 90s and humid); hotter than this past Sunday when it started giving me trouble. I drove through town, some stop and go traffic, and left it set idling for several minutes at a time. No more stalling, so it looks like that was my problem and insulating the hose did the trick.

 

What you saw with the fumes from the bowl was indicative of either fuel boiling or a small air leak on the suction side. Now you know why most 460 trucks sold in the south had the hot fuel handling package. Here where e frequently have 100 + days and you have the AC on also vapor lock isn't at all uncommon.

 

Well...it happened again. I've been driving it to work about once a week for the past month and last weekend I took it on a 250 mile trip in mid 90s temps with absolutely no problems. This past Thursday I drove it to work without any issues, then on the way home I stopped to get the mail and left it idling. I got back in, drove about 100 feet and it stalled. I walked back to the house and got some gas, primed the carb and it fired right up again. Drove it another 100 feet and it stalled again. After priming it again it fired right back up and I was able to make it back to the house but it stalled a third time as I was pulling it into the shed. The temp was in the low 80s that day, not as hot as it was before when I was having trouble. I was exhausted so I just left it until this afternoon when I finally got a chance to look at it. Before trying to start it I pulled the line off the carb and started cranking. Within seconds I had a strong stream of fuel coming out.

Very frustrated right now. I've checked over all the lines and I cannot find anything that is routed any differently than it was before. I've been driving this truck for over 15 years and never had any problems until now. I'm going to check the output pressure on the pump but it seems to be pushing plenty of fuel. I'm hesitant to install an in frame electric pump because of reliability issues but I'm at the point where I'm afraid to drive it anymore because I don't trust it.

 

I wonder if they changed the formulation of the gas in your area recently? Perhaps they've started adding alcohol to it, or more of it. Perhaps one of the timing controls, such as a ported vacuum switch, is messed up so that the timing doesn't advance, building up more heat in the engine. Lots of possibilities.

 

Alcohol has a relatively low vapor pressure compared to many of the other constituents of modern gasoline.
Like butane and propane.

Oil companies use different formulas all the time.
And a lot depends on the season, current market value and demand for the chemicals that make up gasoline.
(Shell "Nitrogen Enriched" gasoline contains certain amines, for example)