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2012 Silverado with BRC IMPCO problem

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  • 2012 Silverado with BRC IMPCO problem

    Is there a way to easily check fuel rail pressure on a bi-fuel 2012 Silverado with BRC IMPCO system...see pic. I can easily check pressure on my Ford dedicated E350 with the schrader valve under dog house but it doesn't appear that simple on the Silverado.

    Problem: My Silverado has full cng tank however when it goes into cng either automatically or manually (pushing button on fuel gauge) the engine will act like it's running out of cng and stop running. No beeping light...just stalls out. Here is what I have done so far...1) changed filter even though it looked like the day I replaced it with a new one almost 15,000 miles ago. 2.) Hard restart...disconnected battery for 24 hours. 3.) Disconnected fuel rail pressure sensors and fuel rail temp sensors, cleaned and made sure they had a good connection.

    What is different from a similar problem I had a while back when the light would beep and switch over to gas, this time the light doesn't flash or beep and engine shuts off. It will run for approx. 1 minute on CNG but then stalls out. Starts right back up on gasoline but acts up after hitting the cng button.

    It seems like the next step would be to check fuel rail pressure in order to verify the regulator is working properly but maybe someone has had similar situation???

    Even though there aren't any cng shops near me, I will head to dealer on Monday to see if there are any hidden codes that could identify a sensor issue or something similar. I had 0 codes on my handheld OBD reader.

    Thanks for your input.

  • #2
    This does sound like a faulty regulator. It could be as simple as a faulty fuel lockoff solenoid too.
    You might try calling around to see if any of the old IMPCO dealers have a regulator on the shelf.


    • #3
      Thanks John! Took the truck to dealership today, we feel the regulator is working properly because the truck would run on CNG for a while. While under the hood, we noticed the fuel lockoff solenoid was very hot when running on CNG. Might have a faulty or shorted solenoid which would explain the truck running on cng for a few minutes and then locking off natural gas (solenoid closing off fuel due to being too hot) which stalls the engine. I've been looking for the solenoid which appears that an IMPCO dealer (OEM Systems in Oklahoma who installed the IMPCO system) might have located. See attached pic. Hopefully that will solve the problem, if it does, what could cause the solenoid from failing or shorting out? Maybe a bad connection and when traveling up/ down the rough mtn rd. we live off of it was messing with the solenoid, over time, failure?? Waiting on a price....


      • #4
        This solenoid, along with all of the components in the conversion system on your truck, was primarily designed for use in small European natural gas vehicles; so durability on pickup trucks for off-road use here in North America presented a challenge. When GM later chose IMPCO for its official OEM program in 2013 many non-BRC components were specified for this reason.

        Its important to lock off your fuel when the vehicle is off, or if the air bags deploy, so you can't just bypass having this on the vehicle. There are a variety of lockoff solenoid suppliers, so if OEM Systems doesn't have what you need then you could call around the list I provided (also try Lancer Automotive at 801-268-8863). Just make sure the part is rated for 3600 psi [248 bar] working pressure / 4500 [310 bar] maximum pressure, the energizing voltage & amps match the solenoid you are replacing, and that you are trained to safely replace this high-pressure part!


        • #5
          If the valve is OK then there is no disassembly of the system. The coil should be able to be removed from the valve and tested for resistance to see if there is a short in the winding. Should be an easy fix if a replacement coil can be found.


          • #6
            It sounds to me like you may have a lack of fuel pressure. But you need to verify that in order to continue with your diagnosis. I would recommend using a scanner that can show you PID data. Look at the fuel rail pressure sensor or FTP pid. That vehicle will most likely need to have 100 to 135lbs of fuel pressure. If you don't have a scanner that can do that. Then another quick and easy way to see if the vehicle is not getting fuel is to hook up a small propane tank to one of the intake manifold vacuum lines, start the vehicle and when it starts to run rough and want to stall. Turn on the propane tank valve and see how the vehicle reacts to it. If the vehicle stops stumbling and the idle smoothies out then you know the motor is lacking fuel. Now you will need to figure out the reason. Injectors plugged? Regulator not allowing fuel to the rail? Wiring to the lock off solenoid?


            • #7
              OEM Systems does have the part...$149.00 which isn't too bad. I am hoping this will fix the problem. Is the solenoid suppose to get very hot when running on CNG? The dealer who checked it out mentioned that the solenoid shouldn't heat up like that thus the reason why we feel it is the problem. We will see.


              • #8
                tennessee did this fix your problem? thanks