I have 160 miles on my restored 83 f150 and when I hit the interstate for the first mile or two the engine is responsive. After that the truck's response starts going flat and will gradually stumble down to only being able to barely maintain 45 mph. If I pull off the interstate it will do fine going up to 45 mph but taking it faster you can certainly feel it slightly stumbling. If I stop the car a let it idle it can reset itself somewhat but will do the same order of symptoms once back on the interstate. The truck is all new: 302 engine, new battery, new cables, high flow cat, muffler, poly tank, fuel pump, fuel & air filter, carb (Edelbrock 1403 - 500 cfm)...small inline fuel gauge reads right about 6 psi. (idle and when revving) but I can't see what it doing under the hood when it acts up. Stock emissions has been kept in tact...as best as possible (thermal ported switches, egr, smog pump, charcoal canister, heat riser (functions). All gauges show normal and symptoms have happened with 1/8 tank or full tank of gas.

I've tried replacing a locking fuel cap with the standard stock one since a few times when I removed the cap it would flow a fair amount of air., Checked wires at coil. Wondered if the fuel filter could be clogged as the steel fuel line is original but was flushed prior to hook up. Didn't know if ~6 psi could be too high for the carb but that doesn't seem likely to be the cause?? Dura Spark II is original and has dripped some of the underside epoxy like gel. No smell of flooding.

Hope I gave you guys enough info and thank you for taking it in. Any help is appreciated!!

 

Hmm, that doesn't sound good. Perhaps the module has overheated?

 

When the module overheats, the engine dies. When the module cools down, the engine restarts.

But, sooner or later, the module will overheat, BURN OUT. Now the engine will not restart.

 

I think it is fuel starvation. The carb holds a good amount of fuel inside it, and the engine doesn't use much idling and putt putting around town. When you get out on the interstate you start using fuel at a higher rate, and the fuel level can't keep up and recover because there are no stoplights and traffic.

1st thing I would try; Run it down the interstate to create the problem, and leave your gas cap off completely. See if the problem goes away. If it does, then you know you have a tank venting problem.

If you still have the problem after that, is there a way you can extend your fuel pressure gauge hose, and tape it on the windshield? I have done this several times, the hose just makes it through the back of the hood without pinching, and I just tape it to the outside of the windshield where I can see it when driving. You would only have to leave it on there for one test run.

 

I have a module from the junk yard from a similar model that looked much better - will give that a try today.

 

I'll hit the interstate today without the cap and if it still happens I'll rig the pressure gauge where I can see it through the windshield. Will my inline gauge do the trick by running a long length run of hose or would you recommend a gauge that I could tee off the fuel line? Thanks Franklin

 

Swapped the ignition module and ran on the interstate without the filler cap and same symptoms like clock work. Next is checking the fuel pressure under load. Let me know if the inline gauge on a big loop is the way to go or to T off to a gauge.

 

T off to a gauge is the best way. I have used a regular cheap pressure gauge for this purpose.

 

Is the truck still fitted with the cats ? As this is typical bad/plugged cat symptoms.

You will have to do an exhaust back pressure test to know for sure. Again this only applies if the truck still as the catalytic converters.

 

 

I would think if air is getting into the line, then you would have some wetness from the fuel weeping out with the truck off.

Is the fuel line to the tank original? I see "rubber fuel lines are new". How much rubber is in the line? There should be a short piece at the fuel tank, and a short piece from the frame to the pump. There may be a piece near the carb if someone modified the hard line up there. Is that all the rubber lines you have?

You are all around it. You know what the problem is now. Keep going.

 

 

My thoughts, offered for free and worth every penny:

1) Could one of the rubber fuel line segments be kinked? That would easy enough to rule out with a visual inspection.

2) Perhaps when the rubber fuel lines were installed, a piece was shaved loose on the inside and has created a partial blockage. Not sure how to check for this, as the loose piece may retract if disassembled for inspection. Might be easier to just replace them, being very careful not to damage them during installation.

3) That new fuel pump: There's no guarantee it's good. Might be worth gambling $20 on a new one.

 

Are the replaced rubber fuel line sections rated for gasoline with alcohol?

 

I was just worried that maybe there was a very long piece of rubber hose that could have been sucking shut. Along that theme, I have gotten hose from the local store that was wound too tight on the hose reel. It was oval in shape when they sold it to me, and did have a tendency to kink and collapse if I was not careful. I was not very impressed with that, and am careful after that when I buy hose.