I bought this truck used a short while ago. It is an F150 extended cab 4X4 with AOD. It has dual propane and gas and has been run mostly on propane I am told. I believe it because when I switch to gas it pings under the slightest load so I believe the timing has been dramatically advanced for propane.

After driving on gas for about half an hour it quits and won't restart with gas for a couple of days. Then it will run again on gas and ping until the same thing happens.

Someone cut the wires from what I believe is the O2 sensor in the exhaust on the passenger side although the sensor on the driver side is still wired in.

The air induction tubes at the rear of the engine were not hooked up because the valve at the back had a hole burned right through it (looks like it melted from resting against something).

Reconnected the system using a T because that valve is expensive ($132 from Ford).

Still have the same problem. Any suggestions?

Also, should I reset the timing to the original spec to run better on gas or use a timing controller like the MSD variable controller to adjust it whenever I switch fuel?

Any help would be appreciated.

 

Although it is elementary I forgot to mention it is a 302 EFI

 

I could sure use at least some ideas about what to look at, please.

Any thoughts would be appreciated.