Results 1 to 7 of 7

Thread: Sudden Acceleration 6.5 Turbo Help!

  1. #1

    Unhappy Sudden Acceleration 6.5 Turbo Help!

    I own a 1998 K3500 Dually with the 6.5L diesel engine. I have been unable to diagnose this problem, so the vehicle is getting no use for the last year. When you start the engine, it goes into a very fast (1500 rpm), rough idle. Kind of oscillating. It will keep going like that even after warming up. The moment you shift into drive or reverse, it goes back to idle and behaves normally, until you press the accelerator pedal, where it accelerates severely. It doesn

  2. #2
    Join Date
    Feb 2000
    Location
    Montana
    Posts
    11,382

  3. #3

    Default

    The problem became worse with time. I thought that it was related to the bad connector on the previous PMD. Once I replaced it, I had very fast starts but the acceleration problem persisted. I can't remember the code, so I will have to scan it. I do remember that the only code in memory had to do with the "security". After not starting the unit for some time, I usually have to recharge the batteries and the truck will not start until I lock and unlock the doors with the beeper a few times.

    It then starts immediately but will the misfire and acceleration problem described earlier.

  4. #4
    Join Date
    Oct 2001
    Location
    Granby, Missouri, USA
    Posts
    3,081

    Default

    Is there possibly a high idle switch installed? On the '96 and newer models, if the high idle switch is engaged, the engine will revert to normal speeds once the brake pedal is pressed and/or the gear selector is moved out of park.

    Here is info on the high idle modifications:

    http://www.kennedydiesel.com/FastIdleSetup.cfm

    Otherwise, I would suspect a failing PMD/FSD. I have personally seen them fail where there is idling/RPM issues, and have heard of them failing and going to wide open throttle, which can be scary.

    Casey
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  5. #5
    Join Date
    Mar 2000
    Location
    Loyal WI US
    Posts
    10,792

    Default

    Sudden unwanted acceleration (touchy pedal) tends to be more in the pump metering control not moving freely in my experience. I don't know enough about the mechanics inside, but I would probably relate it to rusted/corroded or varnished hard parts from sitting or lack of lubricity.

    The misfire is likely the ECM trying to drop cylinders to reduce the RPM to target.
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
    2016 GMC K3500SRW D/A CC short LTZ

    Custom tuning in house using EFI Live tuning software!

  6. #6
    Join Date
    Nov 2002
    Location
    Martinsville, IN
    Posts
    3,163

    Default

    There are a few ways that sudden uncommanded acceleration can occur. Some are electrical and some are mechanical.

    Here is a shot of the back of the pump with the solenoid cap removed.



    What you see here is the armature sitting against the coil. The next shot is of the armature removed from the solenoid. Notice the wear indication near the end of the pin. It's a little out of focus, I apologize.



    The armature pin slides in and out of the coil based on commands from the PCM through the fuel solenoid driver.

    The next shot shows the pump rotor in the stator distributor. The solenoid actuated metering valve is in the rotor.



    The rotor and metering valve are shown separately here.



    The metering valve is held open (slid aft in pump orientation) by a spring in the valve bore. When the solenoid is energized, the armature pin pushes the valve against its seat to close. The milled slot in the rotor outer surface (top in the photo, aft in pump orientation) with a drilled supply hole from an axial hole is the fuel feed hole to the individual injectors. The other hole that is visible in the outer surface is the inlet feed to the main four plunger pressure pump. There is another hole like this 180 deg away.

    The larger hole at the bottom of the image (front of rotor in pump orientation) is a through hole with another through hole the same size 90 deg away. These holes are where the four plunger pistons operate.

    The next shot is of the distributor stator with the rotor removed.



    The holes in the bore toward the rear (nearest in the photo) are the main supply distribution holes. These holes feed directly into the visible holes for the injection line fittings. The milled slot in the rotor mentioned previously rotates past these holes in sequence. When the holes are lined up, fuel can flow from the rotor to the stator and to an individual injector based on how long the solenoid is energized. The other holes seen toward the front of the bore are the inlet feed holes for the main pressure pump.

    The amount of fuel delivered to an individual injector is based on the the pressure generated at the main pump and the length of time that the solenoid is energized to close the metering valve. Excess volume from the main pump is spilled into the return circuit when the solenoid is de-energized.

    If something in the electrical controls causes current to remain on to the solenoid coil, the metering valve will be held closed causing the full volume of the main pump to be delivered to the injectors in sequence, interrupted only by the fact that the hole in the rotor moves out of alignment with an individual distributor hole in the stator. Likewise, if either the armature pin or the metering valve seize or stick in their bores, the same thing will happen. That is why a failing FSD (PMD) can sometimes cause a runaway. The wear seen on the armature pin in the earlier photo may have caused the metering valve to stick closed or not close at all intermittently, causing surging, stumbling, etc.

    I retain copyright for the photos in this post. I am sharing them for informational purposes only.

  7. #7
    Join Date
    Mar 2000
    Location
    Loyal WI US
    Posts
    10,792

    Default

    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
    2016 GMC K3500SRW D/A CC short LTZ

    Custom tuning in house using EFI Live tuning software!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •