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2500HD Bi-fuel FICM?

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  • 2500HD Bi-fuel FICM?

    Anyone know where the Fuel Injection Control Module is on a 2005 Silverado 2500HD Factory Bi-Fuel pickup? I'm having a problem burning up gasoline in-tank fuel pumps when I take a lengthy trip on CNG. I suspect that the pump isn't getting shut down when commanded or it's not getting the command. The fuel pumps are pressure on demand and they have no return fuel line. If it stays running and no fuel being used I'm sure it's really hard on the pump and may be the cause. When I change the pump again I will be smart enough to put my fuel pressure gauge on it and see if it is trying to pump while running on CNG. Didn't get a chance to, but thought about it.

  • #2
    I converted a 1500 about that year. It had a inverter on the bottom of the bed above the spare tire it was controlled by a pressure sensor on the line under the cab it converted the 12 volts dc to 3 phase and varied the frequency to regulate the pump. we never got the truck to run with the power cut to the pump and ended up using a solenoid to kill the fuel after the sensor. the inverter is a box about 6x10 hope this helps you we found that keeping more than 1/2 a tank of gasoline helped keep the pump cool and made it live longer

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    • #3
      I have thought about tapping a 30 amp switch into the ground and just turning the pump off completely. Will be looking into if there is a pressure sensor in my system. My truck is a factory GM system engineered by Quantum Technologies, so I called tech support there yesterday after I had it towed off the freeway 5 miles after the CNG ran out. They did not help much, but did say that there is nothing different about the gasoline system on the truck compared to a non bi-fuel truck. They also said that the pump is controlled by the PCM which is indicative of something telling the PCM that fuel is not needed or needed. This all happened late afternoon yesterday so I will investigate further now that I have ruled out thinking they were all defective pumps. 4th time in about 16 months.

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      • #4
        The gasoline in tank pump should indeed be off during CNG operation . However, GM in tank pumps are notorious for shortened life if run frequently with less than 1/4 tank of fuel. This advise goes for non cng GM vehicles too.

        The gasoline is the coolant for the pump. In theory, the pump should be able to run 24/7 without getting hot even if no gasoline is being consumed, from the circulation ( think about the return fuel line to the tank).

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        • #5
          The last 2 pumps I made sure there was at least a half tank. So I know that isn't the problem. Something has to tell the PCM that there is a need for fuel pressure or not. That part I believe would have to be the fuel pressure sensor which comes on the pump so I can deduce that isn't the problem. I cannot get to the wire harness (which the one going to the pump and about 8" long is new) until I take the tank out. When I take the tank out tomorrow or Friday I want to back probe the rest of the vehicles harness. I need to know where the FICM is on these. That is all. Hence the 1st sentence on my original 1st post.
          Everything else was added to head off people with questions and help of what I already know, but thanks for trying to help. AND There is NO return line. All 2004 and newer full size GM trucks are pressure on demand. One fuel line, no return. If a pump keeps trying to pump where it will not go it will burn up no matter how much gas there is to keep it cool it will not keep it from burning up in that situation. If it was a loop system like you think that which you said would be true.


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          • #6
            So again, can or will anyone tell me where GM hid this FICM on a 2005 Chevrolet Silverado 2500HD factory option Bi-Fuel pick up truck?

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            • #7
              My mind might be getting faulty but doesn't the FICM only control the Injector transition and provide additional switching to handle the increased power requirements for the CNG injectors? I seem to recall the module was mounted on the firewall---follow the CNG injector harnesses and you should be able to find it. I think when the transition to CNG was complete a pulse was sent to a fuel pump control module to turn off the gasoline pump. This module also was involved in providing a priming of the gasoline injectors prior to changeover back to gasoline from CNG. If you have a "nice" Chevy dealer, he can print out a sheet that will detail the operation of the CNG system along with a chart of the location of all the various modules in the vehicle. There is also a troubleshooting guide available to be used by the service techs in diagnosing problems in the system. It's worth a try.

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              • #8
                Thanks for the info sia47. I did get it back on the road after putting a new pump in. While I had the tank out I went through the wiring harness and found a 7 wire connector under the cab that when I unplugged it showed being somewhat burnt around one pin and corresponding socket. Turned out to the heavier gauge ground of the 2 grounds in the group of 7. So I replaced the connection of just that one with a weather proof connector. Runs great and starts up faster than it did before. Should do the trick, I hope. I also went to my local CNG station an filled up then came home and put the pressure gauge on the gas fuel rail and everything is working as it should thank god. Thanks to everyone for their input. I was definitely stressed over it for the 2 or 3 days.

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                • #9
                  Even though it pulls a little slower on CNG it is what I will be running to pull my trailers this year with gas prices on the increase.

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