Question about Chevrolet 3500

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3003 Chevy Duramax just overhauled entire motor. The truck seems to idle very rough and no power on initial start up then picks up alittle power with hardly any throttle response when peddle to the floor. When I put the truck into drive it wont accelerate with the peddle to the floor or rise in rpm? I cant hear any fuel/Injector knocks. Just replaced fuel regulator censor, and cleaned the mass air flow censor. I have noticed that the speedometer goes upto 10 MPH in park when I try to throttle up the engine. I had a friend who is a GM tech test the fuel pump and throttle positioning censor and everything checks out ok, when the motor finally decides to rev up I can hear the turbo spool up as normal also. Possible ground issue ?????? Any help would be greatly appreciated.

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  • kgall May 11, 2010

    Here is the status update. Just replaced the #6 #8 injectors and readjusted the valves. The motor seems to run smooth now but still has a lag in acceleration when in neutral and no response in drive. I do have a tech2 scanner and have checked out the accelerator pedal position sensor / fuel pump / fuel regulator and everything seemed to check out fine. Even had my local GM technician stop out and check everything with his scanner. The only code that came up was intake air heater malfunction. I also cleaned and inspected the MAF sensor, seemed to be fine. I also visually inspected the engine wiring harness and everything seemed to be fine. So with all that said any suggestions would be greatly appreciated, Thanks !

  • kgall May 17, 2010

    Thanks Molson 02536 for the reply, could I by any chance get my ECM re-flashed at my local dealer ? If not could you lead me in the right direction were I can get my ECM re-flashed, thanks !!



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  • Chevrolet Master
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With the new Duramax that is on your 2003, your going to need a tech2 scanner to address the issues. There are just to many things that can cause your not to have any power from your accelerator peddle.
Have you checked your thottle position sensor (the one on the pedal) the correct name is the APP(Accelerator Pedal Position Sensor). Sounds like there is a dead spot in it. According to alldatadiy, it says to check it with a scan tool without starting the engine, just have the key in the run position.
That way you can use your hand and not your foot. As far as the rpm going up and down, that is probably the fuel pressure regulator valve doing that and it's called a loping idle. some trucks do it so bad that you can hear it.
Long shot, but check your MAF sensor for damaged wire leads and try cleaning it. Regardless your going to need a tech2 scanner as mentioned and here is a link to your engine's wiring harness to your 2003 Duramax.
Thank you for using fixya and keep me posted.

Posted on Apr 27, 2010

  • Harvey N Tawatao
    Harvey N Tawatao May 11, 2010

    If all your sensors are in working order and wire leads, the only other thing that comes up to mind would be a faulty ECM and may need to be re-flashed. Here is some information about your engine and hopw we can find the Gremlin that's keeping your engine from running 100%.

    Fuel Injection Control Module (FICM)
    The timing of the fuel injection is controlled by the ECM through the fuel injection control module (FICM), which is a driver box (a driver is an electronic relay with no moving parts). The amount of fuel injected is determined by the fuel injector "On" time. Current flow to the injectors is controlled by the FICM. The ECM communicates with the FICM through a CAN (Controller Area Network) serial data link.

    The engine uses two types of injection pulses for fuel delivery. Pilot injection is a small amount of fuel introduced to promote combustion efficiency and reduce combustion noise. A normal (main) injection immediately follows the pilot injection. Pilot injection strategy is not used at engine speeds above 2,500 rpm.

    The FICM is mounted on the passenger-side valve cover and is cooled with diesel fuel in order to reduce the heat produced by the electronic drivers. The electrical power required for fuel injector operation is 93 volts DC. As much as 20 amps of current is required to open a fuel injector, while 12 to 15 amps are needed to hold the injector open against fuel pressure.

    Cold Weather Start-Up Strategy
    The '01 to '03 and '06-and-later versions of the engine have the intake air heater (IAH) and glow plug relays located in one assembly. Both relays have a power feed from a 175-amp fuse that is hot at all times. The ECM controls each relay independently and uses self-diagnostics related to the control of each function that includes diagnostic trouble codes. Fusible links provide circuit protection.

    Both the IAH and glow plugs use different control circuitry on vehicles sold in California. These applications use a glow plug controller.

    Cold weather start-ups are achieved at temperatures as low as minus 20 degrees F by the use of glow plugs in the combustion chambers. The initial glow plug heating time varies based on the system voltage and temperature. A lower temperature requires longer heating times. The ECM provides glow plug operation after starting a cold engine, which helps reduce white exhaust smoke and improves idle quality after starting up.

    The '01 to '03 engine used the intake air heater (IAH) to warm the air entering the engine for proper combustion. The ECM operates the IAH to also reduce white smoke during warm-up and after long deceleration.

    The following command logic was common to most applications when the IAH was called for.

    Coolant temperature 50 to 104 degrees F
    IAH commanded on 100% for 30 secondsIAH ramps down to 42% after 30 to 90 seconds of operationIAH will hold 42% for 90 to 500 secondsIAH will ramp to 0% after 500 to 600 seconds.

    Coolant temperature below 41 degrees F
    IAH commanded on 100% for 180 secondsIAH ramps down to 42% after 180 to 300 seconds of operationIAH will hold at 42% for 300 to 500 secondsIAH will ramp to 0% after 500 to 600 seconds.

    The LLY engine uses a glow plug system with a control module operated by the glow plug control module (GPCM). The GPCM connects to each of the eight glow plugs individually. This system uses silver-colored glow plugs that are marked LLY and are capable of providing 1,832-degree F heating within three seconds.

    Hope this helps us lead to the issues, most likely it's going to be something simple that was missed out.

    Keep me posted on this project please and hope this information helped lead you in to something that may have been missed out.

  • Harvey N Tawatao
    Harvey N Tawatao May 17, 2010

    Yes you can have the ECM reflashed at the GM Dealer, or you can try your luck at the Salvage Yard and get another ECM for $50.00 and see if that helps. The other thing you can do which i personaly would do is to send your ECM to, they can ether reflash your ECM to factory or reprogram it with a custom tune for better performance and economy and there programs can be upgraded for life.

    Good luck and hope you get your Sierra working agin soon, but check with the dealer to see if there was any recalls or service TSB to your ECM's programs that my have been missed out.

    Please keep me posted friend.



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