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  • High altitude driving CNG issues...

    my 2001 Dodge Ram 3500 Dedicated CNG is a dog at 6800 feet regardless but recently the check engine light has gone on, and off, 3 times. The 3rd time I took it from 6800 to 8200 with a few passengers the light came on again and I had a chance to stop at Autozone and have them plug in their rudimentary diagnostic device. It said, firstly, O2 sensor front. It also listed pressure regulator as a problem. I am betting on the O2 sensor but am hoping for some input from someone with more experience. I just bought this in a July and am using it as a Taxi here. I bought the O2 sensor from Denso for $95 and would prefer to KNOW for sure that is it.

  • #2
    Re: High altitude driving CNG issues...

    I have a 96 dedicated dodge and have not had an issue similar to yours, including multiple trips to the Park City area.

    I have noticed extended crank times if it has been sitting for multiple cold days, but it always starts.

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    • #3
      Re: High altitude driving CNG issues...

      Aeryck,

      I have moved this posting to the "Other Natural Gas Vehicles" forum so that other will be able to follow it as well.
      Jared.
      Mountain Green, Utah
      2003 CNG Cavalier
      2003 CNG Silverado 2500HD

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      • #4
        Re: High altitude driving CNG issues...

        I do fine in Park City, it's when I go above Park City up the Mine Road, it's a 1 mile stretch of road that ascends 1400 vertical feet

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        • #5
          Re: High altitude driving CNG issues...

          The bottom line on high altitude is this: For every 1,000 ft above sea level your engine will loose about 3% of its horse power capability. So at 7,000 ft you will be down about 21% on Hp. (this is not a linear graph). It is an air density thing.

          Also for every 10 deg F above 70 deg you will loose about 1% of your Hp. Temperature affects air density.

          If you don't like it get a super or turbo charger

          Hope this helps

          Larrycng from quartzsite, AZ

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          • #6
            Re: High altitude driving CNG issues...

            Thanks Larry. So, common high altitude problems with all cars. Do you have any experience with the Conoflow regulator? I was thinking changing the factory reg over to this and changing the fuel filter for preventative maintenance and I am hoping it will at least help with the dogging issue. The o2 sensor helps a ton.

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            • #7
              Re: High altitude driving CNG issues...

              First thing to check, with any regulator, is that the atmospheric breather hole in the in the spring retainer cap is open. It is a small hole somewhere around the size of a paper clip wire. If this hole is not open to the atmosphere the system will run rich (the regulator is altiitude compensating).

              Check the switching rate (to determine if the O2 is working) and fuel trim to see if the system is responding. As the altitidue goes up air density goes down requiring less fuel to maintain a stoichiometric ratio. If the cng pressure goes down the amount of fuel injected for a given time (pulse width) will decrease and the fuel trim should stay the same. Fuel rail pressure should change with altitude. Ford, chrysler, and honda have this information available on the the scan tool.

              As for Conoflow regulators I like them, and they can be adapted with the proper fitting. I wouldn't go changing regulators until the existing regulator is proved bad. Pressure should change about 1/2 psig per 1,000 ft (or about 1 inch HG )

              That the theory. Please take a baseline reading on the system at lower altitude so you can document sytem changes

              Good luck

              Larrycng

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              • #8
                Re: High altitude driving CNG issues...

                Wow, this has been quite a journey. The reason the engine was so terrible at high altitude was a compression issue. These gov't vehicles sit, A LOT. The oil pump and engine must've sat in oil sludge because the oil pump went and took the engine out, 55,000 original miles. I found an awesome engine builder, got a new one built with a 7/70k warranty that includes labor! The new engine has so much more compression it has clogged the fuel system so badly that a pro cleaning did nothing to fix it. My theory is that the new engine is pulling the oil that has obviously sat in the CNG tanks, through the system. So, now, I have a new engine, complete, cooling system, O2 sensor, and the new fuel injectors are on the way, FYI, I found great prices on all of this. I will post again after the new injectors are in and see how it runs. I feel I need to find a shop to pull the tanks, clean them out, and reinstall. I don't know if there are any tank refurbishers, but, that is a niche business that needs to pop up. Any comments?

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                • #9
                  Re: High altitude driving CNG issues...

                  If you really feel it is necessary to check the cng tank, make sure tha all recommended procedures are follow, especially venting the tank before removing it from the vehicle. I would recommend removing the valve when you try to dump out any oil that might be in the tank. I would say that if get over about a cup of oil, I might say you could have a problem, otherwise you would have wasted you time and money.
                  There will always be a little oil in the tank if you have been fueling at a place that has a bad compressor. Make sure you purge the tank with nitrogen gas to push out any air that has gotten into the tank before reinstalling the valve in the tank.

                  Just a few thought, good luck]

                  Larrycng

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                  • #10
                    Re: High altitude driving CNG issues...

                    thanks Larry. I have a remanufacured PCM computer being thrown in tomorrow. The injectors were shutting down. I agree I will not need to go through that process, this is another issue altogether. It'll be interesting to see how the new everything performs on the mine road after the new computer is in. It must've had a bad internal ground or something.

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