I was given a 2003 Ford 150 7700 Series truck from the military to use at my police department. The truck was given to us for free. It only has 63,000 miles on it and is in pretty decent shape. However, the truck came equipped to operate only on natural gas. We cannot get a natural gas pump here where we are so I did some research and decided to convert it to gasoline.


The truck is essentially a hybrid, I think, between an F-250 & F-150. It is equipped with a 5.4 liter engine and 7 lug wheels which makes me believe the drivetrain is essentially an F-250.


I found a donor truck at the local junk yard that had a 4.6 liter engine but I was able to remove the wiring harness from the tail lights to the headlights, everything but the harness inside the cab was replaced. I then removed all of the natural gas fuel lines and pumps and replaced them with the stuff from the 4.6 model truck. I installed the charcoal filter, the gas lines, new tank and pump, vacuum lines, fuel rails from a 5.4, and new injectors. I did some work on the throttle body and cranked the truck up. The truck sounded great just sitting there in the shop at idle. There was a strong gas smell coming from the exhaust.


When I took the truck out for a spin I got a check engine light telling me there was a bad o2 sensor and a bad fuel pressure sensor as well. This was expected because there isn't a fuel pressure sensor in the gas fuel rails and there are no o2 Sensors in the CNG exhaust system. When I drove the truck I got severe engine valve pinging when I put the engine under any stress. I figure the timing is off in the CNG PCM settings.


I took the truck to the local Ford Dealer to get the PCM flashed with a gas program and they said it couldn't be done without a donor truck PCM program. I found a donor truck, a 2003 F-150 XLT Lariet, bought a new PCM that would accept that programming as the existing PCM would not and cranked the truck. Again it sounded great at idle but on the test drive the speedometer went to 100 mph when we were going about 30 mph, the transmission didn't shift properly anymore, the truck ran horrible and shut off on us at least three times in a 1/4 mile test run.


My thoughts on this are the conversion will work and I will constantly have a check engine light because I don't have the sensors need to shut it off. I feel like if I get a PCM Flash program from an F-250 of the same year it might act properly. I just don't know about these 7700 series trucks. Where could I possibly get the flash code to take to my Ford Dealer for a 2003 F-250 to even try ? The dealer says he can't call Ford and get it himself. So what do the experts out here think ? I really want to use this truck to haul and move equipment around for the department and hate not to be able to get it right.


Does anybody out there build custom PCM flash codes for F-150's with various setups ?

 

Also the truck is equipped with the PATS system so I have to keep the anti-theft stuff in mind too.

 

Quite an ambitious undertaking to say the least and you did well.
You need to put Ox sensors in the exhaust just below the exhaust manifolds outlets like a stock gas motor has.
Either swap the whole exhaust system with cats or weld Bungs into the pipes.
What you indicate is that you are not awhere that missing Ox sensors cause the motor to run rich off fixed fuel table because the sensors are missing.
I suspect you also have more codes for open heater circuits and possibly EGR codes as well and even CAT monitor codes..
Put a Scanner on, list the codes here, then address those until all are taken care of.
After that, look at live data to see how well the data range is inside limits and go from there to make any corrections that may be needed.
Good luck.

 

Thanks Bluegrass 7, That does make some sense to me now that I think about it .... If I put the O2 sensors in the truck they are about $40 a piece. Then my next step is to find a harness to connect them to the main harness with as there is nothing there right now. Then I hope and pray that the computer reads the O2 sensors and adjusts the timing accordingly and maybe it takes the pinging out of the engine ? It does not have EGR or fuel pressure but if the timing corrects itself I think I can live with that issue. I just want to get the timing correct and take that ping out of the engine.


Thanks again!

 

The transmission should be a heavier duty 4R100 in the 7700. So unless the donor truck you got the PCM from has the same transmission that may be why you are having transmission issues. You might want to scout around for someone selling a compatible PCM out of a dual fuel 7700 that already has the correct gasoline tune on it.

 

Your into a back yard re- engineering project without knowing a lot about what needs t be done and how things work.
There is no fuel pressure sensor.
The OX sensors do not control ignition timing.
The transmission plugup may be different.
You need front Ox Sensors as a Min..
You need the EGR system.
You need the gas exhaust system in place.
You need the harness to feed power to these area that normally come from fuse #23 in a gas build.


And who knows what else we can't tell at this point.
I can tell you how things work but you need to get the hardware in place first.
Otherwise it's a big hassle.
Good luck.

 

I don't know if it will help you or not, but I have a 2003 7700 propane/gas truck with a seized 5.4 if you need me to check part #s on it or anything.



2003 F150 7700 single cab long bed 2WD 5.4 LPG/gasoline missing propane control box




A-pillar spotlight & dent in the front fender
Sorry for the low quality, this was part of a pic of something else.

 

Thanks Sam I Am. You have exactly what I need. I wish I could get the programming off of your pcm. If I had that I think I would pretty much be in business.

I do realize this truck wouldn't pass emissions testing but we don't have to worry about that here in Alabama. I talked to my Ford dealer yesterday and he is checking the wiring harness for me to see if it has the connections for O2 sensors are tied up in the harness. If it does have the wiring I will go ahead with the screw in bungs and O2 sensors. I don't think the EGR is essential but if it turns out to be, I can do that too. Right now I think I need a pcm with the 5.4 gas and the 4R100 programming. I would have thought a ford dealer would have all of these flash programs at their disposal but apparently not.

Wish you lived closer Sam. What are your plans for that truck? I can get more trucks like this one and I might need a donor!

 

check your messages

 

Also, just throwing this out there, if you get a PCM out of a 1999-04 5.4 Super Duty with a 4R100 it is my understanding that it will not have PATS. SDs didn't get PATS until 2008, but your range stops at 2004 because of the introduction of the new transmission in 2005.

 

Well here's an update on where I am so far.

I found a gas burning F-350 with a 5.4 liter and 4r100 tranny and got the PCM from it. I installed it into the truck and it cranked right up. Yes Sam you were correct that it did not have PATS but apparently it doesn't matter. I can now crank the truck with a standard cut key. I kind of like that I can bypass the expensive keys. I went to test drive the truck and it drove great. Timing was correct and transmission shifting was spot on.

Now the problem, the speedometer and odometer don't work. Apparently the F-350 PCM is looking for a specific programmable instrument cluster. The truck I have uses a non-programmable cluster. I have called the junk yard and will try swapping the clusters out now using the one from the F-350 in my truck. I know my mileage will be off but really don't care. I may get this problem licked yet.

There has to be someone out there somewhere who can tinker with these PCM's and customize the programming in them somehow. I was able to get printouts of the PCM bank codes and the CNG and gas truck units are exactly the same from banks 3-10. There are only two lines banks 1 & 2 that are different. Surely someone out there could have taken my original PCM and just altered those two lines of code. There are additional lines below the bank codes that show the instrument panel codes and ABS codes. I wonder if my Ford techs know what they are doing with the software and if they are really as limited as they say.

 

Yes, that was the whole point in my suggestion of getting a PCM out of a 5.4 SD, the early SD's with a 4R100 do not have PATS so the PCM doesn't care what kind of key you use, only that it turns the ignition lock. At least you got it running. That is a lot farther along than you were.

I finally got the title to my 7700. I am not sure what I want to do with it yet but I am interested to know how you get the cluster working.
Also, the Torque app has a speedometer gauge so you could at least feel somewhat safe about your speed.

 

I'm trying to do a similar thing. Convert a 1998 Ford Factory CNG only 5.4L e250 van to gasoline. I harvested parts off a 2006 Ford e350, but many of the parts seem different so I have to go get more parts anyway.
I need the fuel injectors still, PCM it looks like according to your post and the ECU. Did you swap out the ECU in the firewall of your truck?
I have that as necessary from a guy who converted a similar van. He never mentioned switching PCM modules.

 

Reviving an old thread for some help. I have a good angle on a great condition 2000 F15 7700 that the current owner had converted to gas from CNG a few years ago. For some reason when the shop did the conversion and he picked up the truck the handed him a spray bottle and told him to prime the engine for every start. For some further unknown reason he accepted this and moved on.
So if he wants to drive it he has to get out his spray bottle and prime the engine, then it is good for several hours. The next day he has to prime again. He has tried changing the fuel pump (in tank) twice and the fuel pressure regulator twice. The truck gives him a fuel rail pressure light (he doesn't know the numeric codes). The fuel rail pressure reads and holds 35 psi, he thinks it should be 90.

I really want to be able to take this truck off his hands and get it smogged in CA, its a beautifully looked after truck. Does anyone know the solution to this issue?

Thanks for your help.

 

Two things!
1. At key on the fuel pump should prime the fuel rails for starting.
The PCM should set FI rich, open IAC and go high idle from Temperature and Coolant signals.
Is this happening?
2. Good luck getting CA to accept this conversion.
Check with Ca. state motor vehicle dept. for such a deal. It may prevent you from wasting money.
Good luck.