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Switching Back to gas--2001 Dodge B3500 CNG with expired tanks

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  • Switching Back to gas--2001 Dodge B3500 CNG with expired tanks

    Hi guys--complete CNG newb here in Southern California. I purchased an ex-government Dodge B3500 CNG van with 28k on the odometer, but was disappointed in the range. It also can't go to NorCal as they don't fill expired tanks (expired 2014). This was to be a van that I could take to the local race tracks but the range has prevented that.

    So I decided to switch my van to regular gas. My HOPE is that Dodge created the CNG version much like a bi-fuel in that many of the parts would be dual-use. A few aren't, obviously.

    --removed the center CNG tanks and regulator
    --KEPT the rear tanks as I want to use them for compressed air later
    --I'm in the process of installing a stock 34 gallon tank with stock fuel filler
    --Hi-pressure fuel lines (300psi) will run forward to the fuel rail
    --this is a closed loop system so there will be a return line
    --I HOPE that the injectors are the same for CNG and liquid gas (thinking bi-fuel)
    --a charcoal canister will need to be added to the tank
    --the wiring harness for the fuel regulator is not the same. CNG has 4-5 sensors, including temperature and others. These need to be neutralized with a reflash or new PCM (ECU), or potentially find the resistance values the sensors are looking for and plug in some resistors.
    --I hope that plugging in the gas harness will help the process. Making a small harness is not the end of the world, but I'd rather not if possible.

    Has anyone done this before? Am I on the right track, or have I completely missed something?

    If anyone is interested I can add pictures.

    Thanks in advance.

  • #2
    I think it is do-able if dodge did not jack up the compression. Some dedicated vehicles like Honda did. Not a simple or easy job.

    If you can get all the parts, gasoline injectors, fuel rail, throttle body ,computers, wiring harnesses,etc you will also need to get to a smog station referee to get it documented as being identical to the gasoline version when done. The fuel injectors are not at all the same.

    Best to get all the parts off a single gasoline donor vehicle, and contact a smog station referee first.

    I think the bureau of auto repair or CARB maintains a list of smog referees online. in the LA area , one of the community college auto shops is one.
    Last edited by Lakewood90712; 08-29-2018, 09:00 PM.


    • #3
      I'm "ASS"uming that like bi-fuel, the injectors, fuel rail and throttle body are the same. I think the main issue will be either re-flashing the ECU or fooling it into believing that everything is OKIE DOKIE with the sensors. And you're right, both engines are 9:1 compression which helps me believe that a switch back to liquid gas won't be impossible.

      I'm able to legally license this van in an area that doesn't require smog (rural), so that's not on my priority list. Tomorrow may be a day to see if I can find a standard van donor vehicle for some of this other "stuff". Thanks for chiming in.


      • #4
        It sounds like quite a project you have on your hands...

        Bi-fuel engines typically have two sets of injectors and rails and make a complete switch-over between the two injection systems. I don't think Dodge made a bi-fuel van back in the day but if they did it would be doubtful that they would have used the same gaseous fuel injector for use with liquid gasoline too.


        • #5
          John Mitton that is some solid information. I had no idea that they used two different fuel rails....crazy. Rather than spend time modifying the CNG rail, I'll be scouring eBay for a stock rail and injectors. I'm pretty confident (still) that if I can get the right ECU--or get the ECU flashed--then the conversion will work.


          • #6
            You are doing the right thing by retiring the CNG tanks off of that old Dodge van, especially if they were manufactured by Comdyne (is this what is on the label?). I wouldn't put even 200 psi into one of those old poorly-engineered cylinders from a bankrupt company. Do us all a favor and drill a hole in the neck or sidewalls of these beasts so they can't be filled again.