Announcement

Collapse
No announcement yet.

2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Kent
    replied
    I have had my 2003 2500HD for about 2 years now and I want to know the same thing. I also have a check engine light when not running CNG, it goes off when running CNG. The power is slightly less with the CNG but it's not really bad, I haven't noticed too much hauling but I don't haul often. I have a switch in the dash but I have to hold the switch down to go to gas.... as soon as I let go of it, it goes right back to CNG if there is CNG in the truck. Any help making it switch back and forth would be great.

    Leave a comment:


  • Highmarker
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    Originally posted by siai47 View Post
    You might want to try this if you are adventurous . CNG switchover occurs when the fuel level drops to a certain level and will restart when the fuel level is raised above a certain level. Changing the fuel tank pressure sensor circuit might allow you to change fuel type on the fly without getting a DTC. The fuel tank pressure signal is sent from the tank to the FCIM as shown in the drawing. When the tank is full the sensor has low resistance causing the voltage seen at pin 25 to be nearly 5 volts. When the pressure is low, the resistance is high causing the voltage at pin 25 to be close to the low reference level (not ground). By cutting the Dark green with a white tracer wire and installing a two position three pole switch you should be able to either send the correct pressure signal from the transducer to the FCIM or a false 0 pressure signal making the vehicle switch to gasoline. The remaining pole on the switch needs to be attached to the grey wire. I am not sure if returning the switch to the normal position will restart CNG operation or an ignition cycle wil be required. Again, TRY THIS AT YOUR OWN RISK !
    Just wondering if anyone has tried something like this: Installing a switch on the CNG tank sensor circuit to manually for operation of a Chevy truck on gasoline.

    Leave a comment:


  • jeepzz
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    Now that boat towing season is back, I've gone back to unpluging the CNG connector under the truck when pulling. When plugging it back in it usually take several start cycles (and several miles) to get back on CNG. I've found that you can immediately get back on CNG by disconnecting the battery for a second. If you do it quick, you don't lose your radio presets or clock but it will reset the system back onto CNG instantly.

    Leave a comment:


  • jasonjsimon
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    Just wanted to report that I was finally able to give my truck a trial pull on both CNG and gasoline. I didn't build the switch yet since I wanted to get a feel for the difference between fuels and it was significant. I noticed what I would guess was a 25% increase in power on gasoline over CNG. Would love to have gasoline on demand switching now for steep inclines.

    Leave a comment:


  • jasonjsimon
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    [QUOTE=siai47;35370]The wire harness runs from the tank, down the left side of the truck, across the fiirewall and terminates at the right front fender were the FICM (fuel injector control module--I transposed some letters in the first post) is located. It passes through four connectors starting by the tank with C009 and passing through C008, C002 and ending at C001 which is the connector that plugs into the FICM. If it was my truck and wasn't sure what some guy is posting will work, I would most likely try to connect a test switch near the C009 connector by the tank. It should be easy to get to after removing the tank cover and easy to see and splice the wires (or repair them if this doesn't work). If you want to do it at some other point, the wire colors stay the same through all harnesses. If it works out, you could tap into the harness under the drivers door area or extend the wires into the cab from the C009 connector area. If you want to mess around with this kind of stuff, the CNG supplement for your truck would be a good investment from [QUOTE]

    siai47,
    Have you used this circuit before? Just wondering if it has been successfully used either in the pickup or another car.
    Last edited by Highmarker; 03-25-2010, 07:28 AM. Reason: Tried to fix the quote

    Leave a comment:


  • siai47
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    The wire harness runs from the tank, down the left side of the truck, across the fiirewall and terminates at the right front fender were the FICM (fuel injector control module--I transposed some letters in the first post) is located. It passes through four connectors starting by the tank with C009 and passing through C008, C002 and ending at C001 which is the connector that plugs into the FICM. If it was my truck and wasn't sure what some guy is posting will work, I would most likely try to connect a test switch near the C009 connector by the tank. It should be easy to get to after removing the tank cover and easy to see and splice the wires (or repair them if this doesn't work). If you want to do it at some other point, the wire colors stay the same through all harnesses. If it works out, you could tap into the harness under the drivers door area or extend the wires into the cab from the C009 connector area. If you want to mess around with this kind of stuff, the CNG supplement for your truck would be a good investment from www.helminc.com.

    Leave a comment:


  • jasonjsimon
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    Originally posted by siai47 View Post
    You might want to try this if you are adventurous . CNG switchover occurs when the fuel level drops to a certain level and will restart when the fuel level is raised above a certain level. Changing the fuel tank pressure sensor circuit might allow you to change fuel type on the fly without getting a DTC. The fuel tank pressure signal is sent from the tank to the FCIM as shown in the drawing. When the tank is full the sensor has low resistance causing the voltage seen at pin 25 to be nearly 5 volts. When the pressure is low, the resistance is high causing the voltage at pin 25 to be close to the low reference level (not ground). By cutting the Dark green with a white tracer wire and installing a two position three pole switch you should be able to either send the correct pressure signal from the transducer to the FCIM or a false 0 pressure signal making the vehicle switch to gasoline. The remaining pole on the switch needs to be attached to the grey wire. I am not sure if returning the switch to the normal position will restart CNG operation or an ignition cycle wil be required. Again, TRY THIS AT YOUR OWN RISK !
    So the next question is where these wires can be found on the truck. I may get brave and try it if time allows. It seems pretty logical.

    Leave a comment:


  • siai47
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    You might want to try this if you are adventurous . CNG switchover occurs when the fuel level drops to a certain level and will restart when the fuel level is raised above a certain level. Changing the fuel tank pressure sensor circuit might allow you to change fuel type on the fly without getting a DTC. The fuel tank pressure signal is sent from the tank to the FCIM as shown in the drawing. When the tank is full the sensor has low resistance causing the voltage seen at pin 25 to be nearly 5 volts. When the pressure is low, the resistance is high causing the voltage at pin 25 to be close to the low reference level (not ground). By cutting the Dark green with a white tracer wire and installing a two position three pole switch you should be able to either send the correct pressure signal from the transducer to the FCIM or a false 0 pressure signal making the vehicle switch to gasoline. The remaining pole on the switch needs to be attached to the grey wire. I am not sure if returning the switch to the normal position will restart CNG operation or an ignition cycle wil be required. Again, TRY THIS AT YOUR OWN RISK !
    Attached Files

    Leave a comment:


  • jasonjsimon
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    Originally posted by Chris Sullivan View Post
    I have seriously been considering purchasing a CNG 2500 Chev/GMC truck with a 6.0 engine in order to have more power pulling a trailer than a 5.3 gasoline engine. According to some of the above comments there is a very noticeable difference and loss in power when pulling with cng verus gasoline. This sounds like the loss in power will defeat the purpose of getting 6.0 rather than using a 5.3 gasoline.

    Does anyone have experience from using both a 6.0 cng compared to a 5.3 gasoline? Thanks for the info.

    09 GX
    I may not be the perfect example since my new to me 6.0 liter 2500HD has oversize tires and the gearing may not be the greatest for the setup, but I did own a 5.3 liter Tahoe before this. I haven't had a ton of experience pulling with the newer truck yet, but I can definitely say that on CNG it is a lot more solid and in better conrol of the tow than the Tahoe was on gasoline. I definitely think that it was a worthwhile upgrade, but I'm just trying to plan ahead for some tough pulls this summer. I would like to be able to switch off CNG on demand, even if I had to turn off the engine to go back to gasoline.

    Leave a comment:


  • Chris Sullivan
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    I have seriously been considering purchasing a CNG 2500 Chev/GMC truck with a 6.0 engine in order to have more power pulling a trailer than a 5.3 gasoline engine. According to some of the above comments there is a very noticeable difference and loss in power when pulling with cng verus gasoline. This sounds like the loss in power will defeat the purpose of getting 6.0 rather than using a 5.3 gasoline.

    Does anyone have experience from using both a 6.0 cng compared to a 5.3 gasoline? Thanks for the info.

    09 GX

    Leave a comment:


  • jasonjsimon
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    I know this is an old thread, but I'm really interested in accomplishing the same thing with a 2003 Silverado. Has anyone been able to easily trick the system without a check engine light?

    Leave a comment:


  • kirkbenge
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    I think the easiest way to switch from gasoline to CNG is to stop the car and unplug the power to the Low Pressure Lockout (LPL). Doing this has never given me a check-engine light, but it does require that you pull over, stop the engine and lift the hood (you may be able to do this with the engine running, but I've never tried). When you want to switch back to CNG, just plug it back in.

    In the cavaliers this is very accessible and easy to do. It's easy to find to, thanks to it's blue color.

    I don't know about your vehicle. I have attached pictures of an '01 cavalier engine with the LPL labeled. In each picture the connector plug that you want to disconnect is marked by a yellow box.
    Attached Files

    Leave a comment:


  • CNGfamily
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    Originally posted by Highmarker View Post
    It must be a big enough power difference between gasoline and CNG to make up for this inconvience...
    Sample of three bi-fuel vehicles that I have driven for long enough to see a substantial difference in power: '95 Sonoma with a V-6, '00 F-150 (5.4), and '00 Tahoe (5.3). Of the three, the factory converted F-150 had the least impact but was still significantly less power on CNG. The V-6 mini pickup had enough power to start with to live with CNG even towing (a small pair of waverunners). The 5.3 Tahoe is pretty marginal at best when towing ANYTHING with regular gas when there is any type of grade, and it's even worse with CNG.

    Leave a comment:


  • Highmarker
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    It must be a big enough power difference between gasoline and CNG to make up for this inconvience. I am considering getting a '03 or newer factory CNG Chevy 3/4 pickup. With my '03 Cavalier, I don't notice too much of a power difference, so I "assumed" that the Chevy trucks were about the same...I guess not.

    Leave a comment:


  • jeepzz
    replied
    Re: 2003 GMC Sierra 2500 factory bi-fuel: How do I switch back and forth?

    Originally posted by tntw View Post
    I have a 1998 Chev pick-up with the IMPCO factory set up on it that my son uses at college. It came from the factory with a shut off valve located under the drivers side door and any time we need to tow with it or prefer to run on gasoline and save the CNG we just close the valve. The Check Engine light comes on but after reopening the valve it will clear after a couple of starts.
    Maybe Lancer could install one.
    For now I'm just crawling under the truck and unplugging the main electrical connection going to the tank when I tow. The check engine light immediately comes on but when I plug it back in, the truck STILL stays on gasoline until the light resets and shuts off after a few days.
    Sounds like about the same as what you do when closing the valve only I have to wait to run on CNG again 'til the light shuts off.
    I'm going to continue to use this (unconvienent) method until something better comes along.

    Thanks everyone for your input .

    Leave a comment:

Working...
X