Propane/Gas Duel Fuel
 

Hi, I want to say hello to everyone and I am thankful for finding this forum. I have been reading and using the search. But I cannot find a thread on the problem that I am having.
I have a 2000 Ford F150 XLT Triton V8, duel fuel, propane/gas engine. It will run on either one. But the last couple of weeks it got where it would automaticlly switch to gasoline. You can turn off the engine and start back on propane it may run for 100 miles on propane or 5 miles and do the same thing again. On the propane side it will have service engine soon, but on the gasoline side it does not say that. I really like running it on propane since I sell propane I can get it cheaper than gasoline. Does anyone know what the problem may be. Thanks for any help.

Hi and welcome to the forum :)

Is it the stock Ford converted system?
If it is, they have it set up that if it loses LPG pressure, such as if you were running out of LPG, then it automatically switches back to gasoline.
A partially plugged propane filter can cause that. From Ford the filters are ridiculously expensive so rather than just replacing it you might want to remove it and blow through it to see if there is any restriction.
I've also seen vaporizer problems on these. Usually they will freeze up if there is a problem with them.
The most common thing I've seen though is bad Compuvalves. The Compuvalve is the rectangular box shaped thing that sits over the top of the valve cover/intake manifold on the passenger's side of the engine.
Probably the first thing to do would be to take it to your dealer and have it scanned for codes. Since the "service engine soon" light has been on there should be a trouble code stored in the PCM's memory. Most likely it will just say that there is a trouble code stored in the AFCM (Alternate Fuel Control Module). I forget what the actual code for that is....P1600 and something maybe? They can retrieve that code as well using their WDS or NGS scan tool. I doubt that most scanners such as what Autozone has will scan the AFCM. That should at least get you pointed in the right direction to diagnose it. Hopefully your dealer has someone there with experience on these. They can be pretty finicky and hard to diagnose. They are even harder to work on :(