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  • Bi-fuel Suburban

    Hello, is anyone familliar with the older ANGI systems? I recently bought a 1995 suburban bi-fuel model and am seeking any information regarding these systems. I ran the truck on cng this week but went for a fill up and found that the local clean energy station services higher pressure systems. There is another one 10-15 miles away that supposedly will work on my older system. Today,truck wont run on CNG. Need to refuel? There isnt any support here on Long Island for these units so i would be grateful for any info that will help me.
    Thanks,Paul

  • #2
    Re: Bi-fuel Suburban

    Sound like you need to hunt out a 3000psi station or one that has a dual fueling option. That is a blue nozzle (3000psi) and the yellow nozzle. (3600psi)

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    • #3
      Re: Bi-fuel Suburban

      You are probably due soon for a tank replacement as they generally expire 15 years from manufacture. Depending on how well the vehicle runs it might make sense to get a new or used 3600 psi tank. Will need to check the psi rating on the vehicle pressure regulator too to make sure it can handle 3600 psi. The technician can put on a 3600 fill connector if you do the above.

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      • #4
        Re: Bi-fuel Suburban

        Ohhh. Thank you guys so much for the reply. I was beginning to give up hope. I cant find information regarding my unit or vehicle configuration anywhere on the internet. Forget about local help. Is there a technician anywhere on Long Island? I really do need and like this vehicle and the cleaner emissions is the icing on the cake. Its not intended to be used very often but when the need arises. I found the cylinder date and it is dated 1993! I spoke with CNG and now know about the CE application as well as a safety class i must attend. Next available date is the end of August. Im anxious, partially because the truck suddenly stopped running on CNG. I dont know if it is low on CNG or its something else. The pressure guage under the hood reads approx 2000psi. I havent a clue where the filter is or if anything is servicable by me but i would love to upgrade the system to 3600 if possible. There are 3600 pumps 5 minutes from home! But at this point i dont know if it will even run on CNG. I will keep reading and following posts. There MUST be another owner out there. But really, thank you for the information. It gave me some well needed hope.
        Paul

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        • #5
          Re: Bi-fuel Suburban

          Paul, did the truck run on CNG before you ran out of fuel?
          Angi has it own control box that has intercepts to the on board computer. It does send an fake signal to the OEM computer O2 input (it is a square wave). We observed this on Dodge van conversion.

          I'm pulling this out the old gray matter. The system is simple if you follow the components. The system uses a venturi type mixer in the air intake hose. Following the low pressure NG line back from the mixer you will find a fuel control valve with a vacuum line attached to it. This vacuum line works a diaphram that moves a conical valve the varies the flow of NG in response to the oxygen sensor (it is a feed back system). The low pressure hose will continue back to the low pressure regulator. Follow the small high pressure line back from the LP regulator to the high pressure regulator. Check if the HP regulator will handle 3,600 psi input. If the HP regulator will handle 3,600 psi and the system works good, get higher pressure tanks and enjoy.

          Continuing back from the small vacuum line on the fuel control valve, there should be a electronic vacuum control valve (2 wires) that vary the vary a vacuum signal electronically from the Angi's control box to vary the NG fuel mixture to the engine and keep it at stoichiometric for correct exhaust emissions. I believe the electronic signal to the vacuum control valve is pulse width signal (on time is varied), use a millisecond setting on a good DVOM to see if it is working (if you are just looking at straight DC voltage the lower the voltage the more on time (if you have system voltage at the solenoid you are on the wrong lead)

          The ANGI system will also have a temperature tap, throttle position tap, an ignition hot (12 volt) wire, a ground wire, and the 2 wires to the vacuum control solenoid ( if I remember correctly).

          This system is of the type that will set the system slightly rich and then pull it lean to keep the oxygen sensor happy (biased rich)

          This is what I can remember about the system. Hope it helps

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          • #6
            Re: Bi-fuel Suburban

            You certainly are a guru. Ive owned the truck for a week and was able to run on both CNG or gasoline for a few days. I am able to switch over to CNG from gasoline ONLY if already running on gasoline. BUT, I have to feather the accelerator pedal to keep the engine running or she just shuts right down on CNG. I have been trying to find some sort of schematic to identify at least some of the parts you mentioned. My guage is reading 2000psi right now. A slight decrease since i bought it. I started checking fuses,filters, plugs etc. I manually shut off the CNG from a red valve handle under the passenger door side and tried to start on CNG. There wasnt any change in pressure. Shouldnt the guage have read o psi? I am studying your post carefully, this thread is the ONLY information i have found that pertains to ANGI/GM system. Ill keep trying. Thank you very much.
            Paul

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