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Convert FORD F150 F250 CNG to Regular Gas

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  • Convert FORD F150 F250 CNG to Regular Gas

    Hey folks. thought I would start this thread to chronicle my attempt at converting a 98 F250 CNG factory (light duty same as 150) to run or regular gas. CNG is not an option for me but I can't let go of the truck since it has low miles and runs mint ..

    I realize this wouldn't be worth paying a mechanic but since I have the chance to get a $400 F150 with a slippy tranny, it might just be worth it. I can also scrap the old F150 for $200-$300 so I'm paying $100 or so get all the parts... I have already removed 90% of the CNG components except for the plugs and a few hoses.

    So to start off can anyone chime in with the list of changes that need to be made, and perhaps the time it takes for an experienced at home do it yourself mech who's done many jobs on explorers and F150's with success.

    MY understanding so far is I need to change the following..

    Gas Tank
    Gas Tank filler tube
    Gas Tank straps
    Fuel lines
    Computer module (99 F150 should be same as 98 F250 if not I can go to the wreckers and get a comp for $50)
    Evap canister ? (not sure about this)

    -- the rest I'm unsure of, perhaps plugs and wires etc..

    If anyone can help please add your input.. I will try to make a worthwhile thread with pics and times and the final results.

  • #2
    Re: Convert FORD F150 F250 CNG to Regular Gas

    it should not be to bad as the factory never has done what needs to be done to make a great cng truck. it is just a gasoline motor with different junk on the outside. they do not raise the compression ratio and that would be the biggie as you would not be able to buy pump gas. the one thing I see that might be a problem is it might be considered tampering by the epa as I would expect it to run dirty when compared to cng. and if you have smog checks where you live that could be a problem. good luck also list the cng parts here as someone needs them

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    • #3
      Re: Convert FORD F150 F250 CNG to Regular Gas

      Get ahold of the ford factory service manuals , including the electrical/vacuum line diagram supplement.Complete sets can be found on e bay cheaply. IIRC, the dedicated cng crown vic had an extra box, a cng f/i driver module,I think the p/u did too, might need to be removed and wired as original gasoline. Are U planning to transplant the f150 gasoline engine w/o the bad trans ?
      Last edited by Lakewood90712; 06-15-2015, 08:10 PM.

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      • #4
        I have been thinking about doing the same thing. I have a 97 F250 dedicated light duty that has been sitting in the garage for years in excellent shape in many respects. I was going to make a flat bed out of it. I thought about getting new tanks but nowhere to fill up the thing. New tanks are worth more than the truck so not worth it. I have torn a lot of the front end apart, cleaned and bagged everything and the whole project just sits waiting LOL.
        One thing you will need is a gas intake manifold or at least that is what i am told. I think the best bet is to sell the CNG parts on here which will raise most of the cash for the conversion. The crash driver module that sits in front of the rad should trade out for decent bucks as well as the filter setup and electronics. Hoses should be replaced i would think, so no value there.
        I have lost interest in pursuing the CNG thing and would dump the whole truck in a second if i could get something for it worthwhile. Like a trade for a 1993 6.2 diesel engine. Anybody got one they want to trade??

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        • #5
          PaulC did you ever finish the convert process? I'm looking at a 2003 f150 5.4 that I would like to purchase, but it's a CNG truck. I only intend to use regular gas. Can I just remove the tank that's in the bed and drive it around like that? I'm worried about SMOG inspection too though...

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          • #6
            consider the time and effort and cost of decommissioning a cng truck, ever consider the cost of getting a home refueling compressor (used or new), keep carpool eligibility and get your fuel cost down to 65-75 cents a gallon

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            • #7
              I have recently done this/ in the process. I have a 1999 F-250 (regular cab).
              I took out the old tanks, fuel lines, and fuel rail. I picked up a tank, filler neck, fuel pump, fuel lines, injectors, and fuel rail from the junkyard off an 2000 f-150 and the fuel rail off an expedition (had short mounting brackets and was wider). Cost $100. One tank strap fit (rear) but the other I had to weld one end and bold the other to the underside of the bed. Rails and lines fit nicely. To wire it up I hooked up positive and negative wires up from the cng wire harness to the gas fuel pump connector (+red w/ black stripe -black). @ this point it turns on and drives fine (start up can be weird sometimes). There were 4 wires. The other 2 are for the fuel level sensor. I haven't found were they go but I suspect the are up near the fuel rail (btw there 3 unused cng fuel rail clips. I read the one w/ 3 wires is the pressure level sensor). The check engine light is on for low fuel pressure and high temp fuel (might be fixed with swapping computers). There are also 2 fuel vents off the tank I did not hook to anything bc it needs a vacuum tank/pump and hoses the run the length of the truck up to the egr. The vacuum and computer should fix the CEL.

              I converted it to gas bc the cng fuel stations are not very close and they are the same price as regular gas.

              Total cost

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              • #8
                Hi RSA.
                Perhaps we've been speaking about this outside the forum?
                Thanks for your post and enlarging the knowledge base.
                Very interesting to hear about the error codes.
                However, they may be completely inaccurate if the CNG PCM is still in there. It's likely trying to compare your now gasoline fuel and injector rate with expected CNG flow characteristics.
                I know the CNG fuel is at much higher pressure at the rail and the injectors have a higher flow through rate.

                So you were able to use the existing wiring harness - the one that is bolted into a small black box type of thing by the driver side front and runs all the way back to the end of the van?
                And you are still running the original CNG factory PCM? It can start up on it's own when cold - is that possible?

                The CNG has no EGR in place and no inlet on the exhaust manifold for it. It would have to be made from scratch.
                You may be referring to the SAI (secondary air injection) / Emissions / Vapor recovery whatever you want to call it.
                There is a solenoid at the back of the vehicle mounted at the charcoal filter / vapor recovery box. When the engine detects it's fully warmed, at certain points then, it opens and allows the now 'cleaned' gas fume vapors to go back into the intake area on top of the engine and be mixed and re-burned in the cylinders and eliminated.

                I would really like to get that system working correctly if possible.
                Even installing all this though (vapor recovery / SAI) - I cannot think the CEL / MIL would be fully cleared. I know the CNG is missing one 02 sensor altogether, no EGR system, and likely several other differences in sensors etc... It seems like it would be quite hard to get them all working in sync with a proper gasoline PCM but who knows? It's likely beyond my mechanical scope anyway. And leaving in the CNG PCM with gasoline fueling the system... I can't see how the CNG PCM will ever be happy and stop squawking about error codes.

                Any more details you can share are appreciated. I plan to do this fairly soon and would post the entire process and if I can get it running even MPG comparisons etc...
                Last edited by GreenMM; 07-12-2017, 10:22 AM.

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                • #9
                  I have a confirmation from last week from another similar Ford F150 CNG --> Gasoline converter that the newly modified fuel system is working and starting without swapping the PCM. Again, I am very surprised. Doesn't seem to be possible. They are going to email me updates from test running it on the highways etc... I will be doing this all myself fairly soon, this calendar year. I will post much detail here and on the Ford trucks forum when I do so.
                  Last edited by GreenMM; 07-18-2017, 06:13 PM.

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                  • #10
                    I have an f150 7700 that was converted from CNG to Gas. The mechanic did a poor job and i have to prime the engine with a spray can every time i want to start. I've changed the fuel pump, the pressure regulator. I get a fuel pressure rail light and it holds 35psi vise 90 psi. Any one know whats going on here and how to fix it?
                    Did anyone have issues with smog tests after changing from CNG to Gas? Thanks for your help.

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                    • #11
                      Edit, after the prime it is good for several hours but i will have to prime again the next day. Its a great truck with low miles and i want to be able to get it running and smogged in California.

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                      • #12
                        Originally posted by lewisc View Post
                        Edit, after the prime it is good for several hours but i will have to prime again the next day. Its a great truck with low miles and i want to be able to get it running and smogged in California.
                        I am not going to say impossible, but in CA it's the equivalent to a powertrain transplant, not an easy task at all... Save your money, sell it to someone in a state that does not require smog tests, and buy a truck you can get registered without a big hassle.

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                        • #13
                          Thanks for the replies. Ill be moving from the deal.

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