"vapor lock" -like symptoms

Our 1994 Class C RV with a Ford 350 engine will not sustain a trip over four or 5 hours at an altitude of 6000 feet or more. While trying to climb even a mild hill it cannot pull it’s own weight. We can idle the engine and it will rev up but as soon as we put it in gear and try to accellerate it coughs, sputters, and almost dies. If we turn it off and let it cool for 30 minutes, we can start on our way again, but after a few miles or hours it acts up all over again. We have had the entire fuel system overhauled, including a new fuel pump in the gas tank. We have gone through two good mechanics and they do not know where to look further. CAN YOU HELP?

Could be a heat-related intermittent electical problem. Fords of some vintage - maybe yours - have an ignition module (maybe by a different name) in the distributor. It signals the coil when to fire a spark, like points did in older ignition systems. They tend to fail intermittently when very hot before they fail completely.

If you have feeble or no spark when your engine can’t run well, look into the ignition system.

Carb icing can give the same symptoms you describe. After the ice melts the car can run. But I don’t know how your engine lets warm air into the carb (more likely throttle body) but if this system is not working ice can slowly close plug up the throttle body.

I’m not familiar with Class C RVs, but Ford engines of this era used the TFI-IV ignition module which is very prone to failure. Look at the distributor on the front of the engine; if it has a small rectangular, gray module mounted on the side that is the TFI module and could very well be your problem.

The symptoms of the module will vary but generally it resembles running out of gas. The failure to start until it has cooled down is another symptom and the failure can also be erratic in nature. It may run fine for an hour, a day, week, who knows, before it quits again.

It’s a comparatively easy and cheap fix also. If you want to know a bit more about this problem, here’s a link.

It’s very easy to suspect the fuel system when this problem occurs as the symptoms are so similar. Hope that helps.

It could be vapor lock. Usually in a fuel injected car, the fuel won’t vaporize because it’s under pressure, but the ethanol they’re adding to the gas in some places these days vaporizes at a much lower temperature than plain old gas. What can happen is that on a fuel injected vehicle, it pumps fuel up to the fuel rail or throttle body and injects it into the engine on demand, but whatever doesn’t get used gets sent back to the tank. This has the effect of gradually heating up the fuel in the tank until eventually the fuel coming from the tank is warm enough that it will vaporize even when under pressure.

You or your mechanic may need to do some rearranging of the fuel lines. If there’s any lines that run close to an exhaust component or anything else that gets very hot, they may need to be re-routed or insulated. My Honda’s fuel filter is very close to the engine and vaporlocked very badly when we went to South Dakota last summer-- I wrapped the filter up with some foam insulation and I haven’t had the problem since.