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chevy 2500 bi fuel problems

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  • chevy 2500 bi fuel problems

    I have a 2002 chevy 2500 bi fuel and it is running poorly on CNG. it does not idle and has no power. on gas it runs great and no issues. I took it to a local cng shop that came recomended and they diagnosed it wrong twice! after i flushed 1200 bucks down the drain I figured i might look to this forum for help. replaced injector, intake maifold gasket, map sensor, all oxygen sensors, cleaned injectors. I am out of ideas help!

  • #2
    Re: chevy 2500 bi fuel problems

    danoboy,

    I moved this thread to the GM/Chev Vehicles forum so the experts can chime in here.

    Have you had the CNG filter replaced? Did the CNG shop look at the high pressure regulator?
    Jared.
    Mountain Green, Utah
    2003 CNG Cavalier
    2003 CNG Silverado 2500HD

    Comment


    • #3
      Re: chevy 2500 bi fuel problems

      they told me it didnt have a filter, but I found out it did and replaced it today. the old filter had broken apart and I dont know where those pieces would end up, but a chunk of it came out of the line past the regulator. I blew the lines out with air but still no change. it purrs like a kitten on gas, so I dont know. I am looking at the injectors now to see if parts of the filter are clogging them.

      Comment


      • #4
        Re: chevy 2500 bi fuel problems

        There are two filters on the system. The one you have replaced and one inside the high pressure regulator which Highmarker mentioned. Are you sure you didn't find pieces of the filter material at the inlet side (center) of the high pressure regulator? The drawing that I have of the system on your truck shows the paper filter is located between the High pressure lockoff valve (tank valve) and the high pressure regulator. I thought those were on the outlet side of the HPR but no matter. In the center of the high pressure regulator is a small filter that is accessible by removing the high pressure fuel line and then the fitting that the line screws into from the HPR. You will find a small spring that you can pull out with a small hook tool and then the filter element can be removed and cleaned if necessary. That should have caught the filter material. If the paper filter is downstream of the HPR then the next place the filter material will end up is in the low pressure regulator which is mounted on the drivers side valve cover on the engine. This regulator can be serviced by removing the cap on the top of the regulator and seeing if there is any filter material in there. If you find anything in there, it needs to be cleaned out and put back together. Also, because there are no further filters in the system, the injectors should be removed and with a strong light look in the inlet end of the injector at make sure there is no material in the screen inside the inlet. If the fuel system or an injector is plugged, this vehicle should be getting a check engine light and several DTC's (codes) relating to fuel trim, misfire, etc. Some of these codes lead you to things like the heated oxygen sensor, map sensors, etc. However, if the vehicle runs fine on gasoline (and these sensors are shared in CNG operation) they usually aren't at fault. The only other area to look at is the bank of relays located on the firewall that control which set of injectors (gasoline or CNG) are operating. This is controlled by the fuel injection control module and if there is a failure of one of these relays, it should be monitored by the FICM and throw a DTC along with changover to gasoline. BTW, almost all the lines and fittings you will be working with have seals that look like "O" rings but are not. Many are "O" ring face seals and will not interchange with a "O" ring. So, if you are reusing the seals, make sure they are not damaged, make sure you put the seal back on the fitting that it came from and use Vasoline on the seal to lube it before tightening the line. The lines need to be tightened up snug but they aren't pipe fittings so you don't want to reef on them like a tapered fitting. Good luck on this, I am sure you will find the problem.

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        • #5
          Re: chevy 2500 bi fuel problems

          thanks siai47, I will check those things in the next few days and get back to you. I looked in the HPR and there was a small metal filter but I didnt see anything, but I will take it apart and clean it out. I noticed some times there is a hum coming from the low pressure regulator on the driver side. I dont know if this is related or normal. again thanks for the detailed info.

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          • #6
            Re: chevy 2500 bi fuel problems

            stupid question, have the plugs been changed?
            GM World Class, F1 Cert
            05 Crew cab 4X4 Silverado LS
            03 Cavalier
            01 Cavalier (sold)

            Comment


            • #7
              Re: chevy 2500 bi fuel problems

              ya I changed the spark plugs a month ago. also I have an update. I pulled the system apart and cleaned any areas that could have the filter material in it. I found small parts in two of the injectors but I think the shop cleaned them out as well. siai47, I took the cap off the low pressure regulator, but I didnt see any filter. is this normal? any way I think I have the system cleaned out. I got it to idle alot better, when before it would die at idle. I took injector 2 out that was loud and replaced it with the one that the shop said was bad and it works a million times better, the only problem is that I still have no power when I put my foot down on the pedal. I might replace the plugs again and see what happens, but I am going to drive it on gas so i can get it inspected. where can I get the service manual for the 2500 system? is it available from the dealership?

              Comment


              • #8
                Re: chevy 2500 bi fuel problems

                No, there is no filter in the low pressure regulator, however if any crud is in the system it can end up under that top cover and mess up the operation of the regulator. Service manuals sometimes end up on E-bay or can be purchased from GM through www.helminc.com. You are looking for the CNG supplement.

                Comment


                • #9
                  Re: chevy 2500 bi fuel problems

                  I had it running ok but I have some dtcs that I am confused on and wondering if maybe a relay somewhere or something. the codes say that it has problems with the fuel pressure and temp on the passenger side and it is not communicating with the oxygen sensor bank 1 sensor 2. is there a relay or something that would cause this?

                  Comment


                  • #10
                    Re: chevy 2500 bi fuel problems

                    Hi I am new here and have a question regarding maintenance on a 2004 chevy 2500 bi-fuel van. I have had it over 4 years and only occasionally had some rough idling when using cng, on regular gas it has always run really smooth. I recently moved out of cng fueling station range and for the last 5 months used only gas with 10% ethanol. I noticed that it doesn't start great lately and runs a little rough on gasoline sometimes. After reading other posts about changing the plugs, wires, distributer and cap I realized I am overdue for a tune-up. I bought this van with 112,000 miles and now have 178,000 miles and never changed the plugs. Do you have any suggestions for service when out of cng mechanics area. I called the gm dealer and they want over $550 to change the plugs, wire harness and remove any carbon tracings. Is this a job that must be performed by a dealership or can goodyear or firestone perform the same service for a lot less? I just worry that there are some special components, etc. that are specific to a cng vehicle and that they will unknowingly mess something up. Any thoughts? One more question, is there a fuse on this vehicle that needs to be unplugged if not using cng for extended periods of time?

                    Comment


                    • #11
                      Re: chevy 2500 bi fuel problems

                      an update. the codes that are there now say the circuits for the oxygen sensor bank one senor two are not responding. any ideas?

                      Comment


                      • #12
                        Re: chevy 2500 bi fuel problems

                        As a new member I can't open a new thread but this isn't a hijack either. I too have a 2004 Chevy 2500 bi-fuel that has rough idle issues on CNG only.

                        Following siai47's excellent tutorial/advice, I replaced the wires and plugs (183K miles OE!). It helped a little but not a fix. It is also throwing codes P0307 is most common (cyl-7 misfire) but occasioanlly cylinder-2 or just P0300 multiple misfires - again ONLY on CNG. It purrs on gas which rules out ignition in most cases. O2 sensors are all reading about the same .8 at idle (better on gas than on CNG) but no codes.

                        My next step is to inspect the filters. Does anyone have a diagram or pic of which ones/where to inspect. I will re-read the above post but it didn't spell it our for me initially and I'm not sure alldatadiy would have CNG support manual (but I will check).

                        After that, I am thinking it would be in the injectors perhaps? My concern is that I don't notice the miss above 2500 RPM's. It could be there and just masked (the computer sees it apparently) but I would think a clogged injector wouldnt smooth out any at RPM but I don't really know if that is possible or not. Would a balance test show me if this was an issue?

                        so, I would love some more detailed trouble shooting from the Guru's like siai47 and woudl like to see danoboy figure his ride out.. I love tinker and wrench. I only have a OBD scanner that feed into Torque or the other software for windows but I can get a lot of data from it.

                        Comment


                        • #13
                          Re: chevy 2500 bi fuel problems

                          Originally posted by blufie View Post
                          As a new member I can't open a new thread but this isn't a hijack either. I too have a 2004 Chevy 2500 bi-fuel that has rough idle issues on CNG only.

                          Following siai47's excellent tutorial/advice, I replaced the wires and plugs (183K miles OE!). It helped a little but not a fix. It is also throwing codes P0307 is most common (cyl-7 misfire) but occasioanlly cylinder-2 or just P0300 multiple misfires - again ONLY on CNG. It purrs on gas which rules out ignition in most cases. O2 sensors are all reading about the same .8 at idle (better on gas than on CNG) but no codes.

                          My next step is to inspect the filters. Does anyone have a diagram or pic of which ones/where to inspect. I will re-read the above post but it didn't spell it our for me initially and I'm not sure alldatadiy would have CNG support manual (but I will check).

                          After that, I am thinking it would be in the injectors perhaps? My concern is that I don't notice the miss above 2500 RPM's. It could be there and just masked (the computer sees it apparently) but I would think a clogged injector wouldnt smooth out any at RPM but I don't really know if that is possible or not. Would a balance test show me if this was an issue?

                          so, I would love some more detailed trouble shooting from the Guru's like siai47 and woudl like to see danoboy figure his ride out.. I love tinker and wrench. I only have a OBD scanner that feed into Torque or the other software for windows but I can get a lot of data from it.
                          I also have a missfire in mine and have found the valve's to be sticking with 7600 hrs and 186k miles it is due for a rebuild. You can check the flow of the injectors with tech II special functions injector balance test, dont even have to open the hood, the fuel rail pressure sensor show you how much each inj is flowing.
                          GM World Class, F1 Cert
                          05 Crew cab 4X4 Silverado LS
                          03 Cavalier
                          01 Cavalier (sold)

                          Comment


                          • #14
                            Re: chevy 2500 bi fuel problems

                            Usually if there is a misfire or rough running condition on CNG only----it is ignition related. However it could also be injector related. CNG is much harder to ignite then gasoline and puts a lot of demands on the ignition system therefore a marginal ignition component could work fine on gasoline but cause problems on CNG. The first thing I would do (you replaced the plugs and wires) is replace the coil pack on #7 cylinder and see if that clears up the problem. A cheap way to do this is swap the coil pack and ignition wire with one from a known good cylinder (one that hasn't thrown a code) and see if the problem moves to that cylinder. If you still have a problem, find someone with a Tech2 and do the crankshaft variation learn procedure. This procedure "lines up" the mechanical components of the engine with the electrical ignition components to compensate for wear. It kind of puts everything back to a zero offset condition to be sure the ECM can control things on either side of zero. While you have the Tech2 connected, do the injector balance test. This will verify that each injector is functioning correctly. The Tech2 will prime the fuel rail with CNG and then pulse the first injector for a preset period of time. For example the fuel rail pressure might be 35 psi and drop to 26 after a pulse. Each time you do the test the Tech2 moves to the next cylinder and the fuel rail is re-primed and both pressures are written down. If you have a questionable injector the pressure drop will be out of line with the other injectors. The final pressure isn't important. What is important is that the final pressures are all within a couple of PSI of each other. If a injector is functioning but reads out of spec with the others, it can be cleaned if necessary. Finally, there are two filters on your truck. The most important one to change is under the tank cover in the bed of the truck. After you get the cover off, you will see it mounted to one of the tank straps with a line going to the tank valve. If you don't feel comfortable doing the following, don't do it. You are working with up to 3600 PSI pressures that could injure you or kill you if something went wrong. You need to depressurize the system by removing the connector going to the tank valve then starting the engine and watching the fuel gauge go to empty and then changeover to gasoline. At this point there will still be some residual pressure in the filter. With a allen wrench you need to slowly remove the bottom drain plug and bleed off any remaining pressure. If the filter body starts to turn when you try to remove the drain plug you must hold it with a wrench to be sure the plug is loosened first. Make sure there is no pressure left before fully removing the plug. If there is any condensate in the filter, it will be leaking out first (and making a mess) before all of the gas is released. You can then take a large wrench to remove the filter body and change the element. GM has a kit with the element and "O" rings to do this job. Clean the filter body, put vasoline on the "O" rings, slide the element into place and tighten the filter body and drain plug then reconnect the electrical connector at the tank valve. Remember these aren't pipe fittings so the body and plug just have to be snug, not tightened by a gorilla. Restart the engine on CNG and check for leaks with soapy water around the filter housing. You might have a check engine light after running the engine with the tank valve connector removed but it will clear itself after a few engine starts. If not, a scan tool will clear it or disconnecting the battery for a few minutes will a clear the check engine light. The second filter is on the high pressure regulator but shouldn't be a problem due to the fact that the primary filter takes care of most of the crud that could get to it. I wouldn't worry about it as it is little more difficult to change and usually isn't a problem in these vehicles. A misfire is a real problem on any CNG vehicle as it is more likely to do serious damage to the catalylic converter due to the higher exhaust gas tempertures found when running on CNG. This quickly melts the catalyst plugging the exhaust system. If the truck feels sluggish on CNG or gasoline have the converter(s) checked for damage.

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                            • #15
                              Re: chevy 2500 bi fuel problems

                              Thanks to all for the replies! I will swap some coils packs around and re-test. I am a bit worried about how much it might have been driven in this misfire condition and what it may have done to the cat element. It seems to pull and have power on gas but I don't know how quick this heavy truck should be. I wonder if a plugged cat is danoboy's problem (no power)?

                              As for the crankshaft variation learn procedure, should that be done while on GAS or CNG, or does it matter? Seems like since the CNG is the fail point I would want to do it on CNG but if it is rechecking the spark/cam/crank sensor communication and timing, then either fuel should work I suppose. I would really like to do the balance test and the recalibrate - wish someone rented tech II's!!

                              If none of that helps, I am comfortable with the fuel filter proceedure assuming that the tank valve is actually sealing. I had a friend with a ford that the valve in the tank never seemed to closed properly and we had to let it blead out last year when we needed to replace a cracked idle injector.

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