I have a 93 7.5L F Super Duty that I am converting from propane to gasoline. It will run very good if fuel is introduced at the intake, as soon as it runs out of the introduced fuel it quits. It has 42 psi at the rail, I checked the injectors with a noid light and it flashes. The fuel pump runs about 2 seconds when ignition is turned on. It maintains 40 psi at the rail when running on introduced fuel. I called IMPCO to see if the PCM was different for propane burners, they said no should be the same. I have been fooling with it for a week on and off now and am out of ideas. Does anyone have any thoughts?

 

Depending on the propane inj system that was used, you may need to swap out the injectors for oem gasoline injectors.

Some efi propane systems use their own injectors added to the intake, leaving factory injectors in place. I'd start by investigating that....if you don't see propane injectors I'd guess o.e. style inj are in your fuel rail currently and need to be swapped with the 24 lb/hr gasoline injectors that the 460 uses.

 

Thank you for the information. It does not have extra propane injectors. I will pull one of the injectors tomorrow and take it down to the local napa store. Am I wrong in figuring that if the injectors are propane injectors they will have a different part number on them as compared to gasoline injectors?

 

I'd guess the numbers are different, unless someone modified stock units (i think thats doubtful) it's worth a shot to do some investigation along those lines. A cheap way to test that as the culprit would be to pull some from the junkyard and see if it runs with the swap. Misewell grab the computer also if you find a 460.

For the purpose of testing only, you can pull some 19 lb inj out of a 5.0/5.8 if you can't find a 460. You can test and idle with the small inj, but you can't use them permanently. The same can be said about the computer, a speed density 5.0 or 5.8 computer will start and run the 460 for diagnostic purposes but can't be run like that.

I'd also look at the map sensor and see if anything funky is happening with it as well.

 

My guess is the injectors are plugged since they may have not been used much.

 

The distributor/PIP

 

Thanks for the ideas guys. I got hijacked by my wife for the day so I'm not going to get to it till Monday. I didn't know that I could use 5.8 parts for a start test. I have a 89 f250 5.8 outside that I haven't used for awhile I can try out these ideas and see if I can nail this down. I will keep you posted on what happens when I get it done.

 

If it was a bad PIP there would be no spark or indication of injector pulses. It also would not run when dumping fuel in the intake.

 

all these trucks were so similar that you can use just about anything from any of them, within the engine management system, to diagnose issues. but this can only be done for diagnostic purposes only for the fuel components, i.e. injectors and computer....you cant mismatch fuel components from 460 to small block for permanent fixes.

 

X2

We have had this same problem before on this forum.
He had to clean all of the injectors because they have not been used. Then it ran OK.

 

what he said.

 

Local wrecking yard has a plow truck that did the same as the OP's truck. Same symptoms. It had 40 psi fuel pressure, fuel pumps worked, power at injectors, it had spark and would run if bottle fed. Stop feeding it and it would die. Tried 3 ECU and no different.
Replaced dizzy and it runs like a top.

 

They didn't change the fuel filter or clean injectors either.

 

Sounds like it was out of time.

 

Thanks for responding guys. Your help is really appreciated. I won't get to this till tomorrow. As soon as I try these things I'll let you know how it goes. All of my mechanical experience is on class 5 trucks and heavy equipment (40 years). I quit working on my cars and trucks back in the early 80's so if it's real old their is no problem diagnosing the problem, anything newer and I'm pretty illiterate. This is interesting learning how this all works. I've never cleaned injectors, what would you recommend?
Thanks again