I Was Wondering if anyone has dealt with converting propane back to gas on a 1990 Ford 250. Can it Run on Both ? My Truck currently only runs on propane and i want it back to regular gas. The mileage is not all that great on straight propane, 8 miles a gallon?

 

There are kits that you can run so that you can operate on either propane or on gasoline. The deal is that you need a two way (Double Pole, Double Throw) toggle switch to control which direction to go. You set it up like this...

Preface: - In most conversions, the fuel pump relay has been removed and the injector harness is unplugged from each injector. (I hope they didn't cut them, which I've seen!) What you'll need to do is to reconnect the injectors, and reinstall the fuel pump relay. This will get the fuel system "operational". Of course, you may need to flush the fuel tank or maybe even replace it. You'll also need to flush the rest of the fuel system and depending on whether or not the system was flushed you may even need to replace the injectors and fuel pressure regulator.

Setting 1: Gasoline - Once the system is able to sustain normal operation on gasoline, you will need to splice into a couple harness wires. You'll have to put the fuel pump relay on the toggle switch circuit and and you'll also have to put the 12v lines of the injectors on the toggle switch. This is not as straightforward as it sounds and needs to be handle via two separate relays, one for injectors and one for the fuel pump relay itself. Theoretically, you could forego the fuel pump relay circuit and just shut the injectors off, but I hate to have the pump running for no reason.

Setting 2: Propane - On the 12v line that goes to the propane shut-off solenoid, just wire it through the second setting of the toggle switch. When you switch to gas, it shuts off the feed of propane to the vaporizer.

When switching from one setting to the next, the engine may stumble for a few seconds, especially going from propane to gas since it takes a few seconds for the vaporizer to bleed down and purge the remaining propane.

I used to have a wiring diagram for such a layout back when I used to do CNG conversions installations, but darned if I know where it is now. If you really need one, I can try to put one together for you.

And yes, while propane is much higher in octane than gasoline, it doesn't have the BTUs and therefore doesn't have the same power output. However, the cost offset of propane usually would make it worthwhile. Nowadays, I don't know. One other thing to keep in mind is that propane is BRUTAL on valves and valve seats. I'd definitely invest in a compression test and see if the any of the valves are leaking.

Let me know if you have any other questions.

Good luck.