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6.5 diesel idling funny

Discussion in 'Chevy Trucks' started by serafii, Nov 16, 2011.

  1. serafii

    serafii Senior Member
    Messages: 287

    So heres the deal. i have my 97 chevy 3500 DRW with the 6.5 diesel with 110,000km. it started in may the truck while idling the rpms would drop and sounded like the truck would stall. id give gas and it would be okay. it would happen maybe once a week. july came around and it was getting worse.

    while driving, it would accelerate on its own. and sometimes while idling at a stop sign it would either drop in rpms or accelerate.(thank god for the brake pedal)

    i changed the frame mounted pump, and the fuel filter. nothing.

    i spoke to someone from a diesel garage and he tells me the solenoid on the injection pump needs to be replaced. a $1200 job that SHOULD fix the problem. im willing to pay $2000 but it HAS to fix the problem.

    just last week the truck went absolutely crazy. i drove it about 20 minutes to work and it went great. started the truck about half hour later, put it in reverse and the truck attempted to go backwards at full pin. again, luckily for the brake pedal. right after that, it shot up to 4000RPM then dropped to maybe 500rpm. once it dropped, i floored the gas pedal down.
    with the pedal down, the rpm would go from 500 to 2000 back to 500 back to 2000.

    it did that for a solid 10 minutes. after that the truck was running fine. the next day, same thing, maybe even worse. dropped it off at the garage because it was getting too dangerous to drive. he called me and told me that my fuel lines and return lines were rotted out that could have caused air in the system.

    tried the truck monday morning, same thing but no high rpms. just low, hesitating rpms.

    im getting annoyed.

    one thing that seemed fishy to me is that the truck has 2 tanks that go down at the same time. same sized tanks. i filled it up sunday night and the rear tank took $25 more than the front one. could that mean anything?

    sorry for the short story guys. im just getting really fed up now
  2. great white

    great white Member
    from Canada
    Messages: 34

    Your pump mounted driver (pmd) solenoid is on it's way out.

    Common failure point on these trucks.

    It can stop the truck dead, intermittently miss and even accelerate when it starts to fail.

    Good new is that it is not a 1200 fix. it's about 500-600 for a quality replacement.

    You need a new pmd and a relocation/heat sink kit.

    One of the best on the market is available at heathdiesel.com

    Great guy with great service. Most experinced 6.5 guy out there. His replacement has a 7 year warranty on it.

    You can find them elsewhere a bit cheaper, but not with that warranty.

    I'm running one right now. Works great.

    Check them out.
  3. Philbilly2

    Philbilly2 PlowSite Veteran
    Messages: 3,767

    Sounds to me like a PMD (pump mounted driver)

    When my PMD went out, my truck was all over the place. Most of the time, it would run like hell for the whole day, then we would stop on the way home, and when we went to leave, it would start and then stall or the RPMs would ramp up randomly or stall out randomly while driving.

    The PMD is the brain box for the 6.5L injection pump. Problem is GM decided to use the fuel that passes past the back side of the PMD box to cool the box... dumb. Also, the PMD is in a spot that no air can get to it.

    If you can find somone around you that has a known good PMD, you can try it and see if it will fix your problems. If not, you can find them on Ebay for cheap (under $250 with a relocation harness and a heatsink. Either way, you need to relocate and place it on a heatsink or the PMD problem will keep happening.

    As for why your rear tank took more fuel. On my 6.5 cab and chassis, I had a little pin leak in the suction line on my rear tank. It caused it to not ever pull that hard from the rear tank. When I would fill the rear tank, it would only take afew gallons. Once I fixed that pin hole, it drains the rear tank first now. If that guy fixed your lines, that is probley why.
  4. Philbilly2

    Philbilly2 PlowSite Veteran
    Messages: 3,767

    As you can see, it took me 15 minutes to type my responce as I am a seak and destroy style typer.:laughing:
  5. great white

    great white Member
    from Canada
    Messages: 34

    I call it "hunt and peck"...;)

    to the OP:

    also check out Thetruckstop.us

    Site that specializes in 6.5's.

    Lots of knowledgeable people about the beast there. They're mostly just regular ol' working slobs trying to keep their rigs running and affordable...very personable, for a web board that is.
    Last edited: Nov 17, 2011
  6. serafii

    serafii Senior Member
    Messages: 287

    I forgot to mention yesterday that the pmd has been changed exactly a year ago. It's been mounted right near the "turbo power" engine cover. It's a stanadyne pmd with the heat sync. Is it possible it's already defective?
  7. great white

    great white Member
    from Canada
    Messages: 34


    believe it or not, that location is worse than the factory location. Too much heat exposure can kill a pmd in under a year.

    Here's the deal:

    Stanadyne mounted the pmd on the pump in order to use the diesel fuel as a cooling medium. While running, it actually does an not half bad job. The issue is shutting the truck down leaves in down it the engine valley bathed in heat with no cooling flow of diesel.

    The relocation kits that mount it u on the intake seem to be a solution at first glance.

    However, what has really been done is the pmd now doesn't have the cooling flow of diesel to cool it while running, it's bathed in engine heat ALL the time, and the only cooling it gets is waste flow (and heat) from the engine cooling fan that's just sort of banging around the engine bay.

    The good kits (like heathdiesel.com, pmdcable.com, etc) relocate teh PMD out of the engine bay on a large heat sink.

    The cooling issue is about thermal differences. Engine heat is around is easily above 100f in the engine bay. The PMD can hit over 150F in operation. not a lot of cooling can take place so your PMD ends up running hot.

    The kits mentioned move it to where ambient air temp are exerienced, usually not much higher than 80F in summer canada. Winter is even better. Couple this with a large heat sink (ie: large aluminum mass, not a lot of fins) and the PMD lives a longer life.

    Unfortunately, your "intake mounted kit" is actually worse than the factory location.

    But they sure look purty!


    Of course, PMD's are temperamental things at best.

    I've got an old spare I keep in the glove box that has more kms on it than I can count. Runs fine. there are lots of guys who have them fail in months.

    About the only reassurance I can offer you is to get one of the 7 year warranty ones. Bill heath at heath diesel steps up when it's time to replace. He's even replaced some out of warranty. He has told me he has some out there that have been trouble free for 10-15 years with his kit. That's pretty good!
    Last edited: Nov 17, 2011
  8. Plowtoy

    Plowtoy Senior Member
    Messages: 929

    Believe it or not, I have seen this happen and cause your type of problem. My buddys 94 suburban did the very same thing as yours is doing and he ended up replacing the rotted lines and the problem went away. Luck? Maybe, maybe not. I wont disagree, the PMDs on those are not in a very good location and seem to fail often, but I think I would get the visual problem fixed before I spent the money on a PMD. Just my .02
  9. great white

    great white Member
    from Canada
    Messages: 34

    While fuel in the lines of a diesel will cause hard starting, stalling and poor running, the "unintended acceleration" symptoms points to a pmd.

    I have never seen or heard of air in the lines causing a 6.5 to accelerate.

    A worn DS4 (injector pump) can cuase erratic rpm also, but has other symptoms the OP hasn't experienced.

    I'm still putting my bet on a PMD....
  10. serafii

    serafii Senior Member
    Messages: 287

    I also forgot to mention that the truck turns over for about 5 to 10 seconds before it starts. If that helps...
  11. damian

    damian Senior Member
    Messages: 330

    best bet in your situation is to replace the pump and make sure the quality replacement uses the new grey color stanadyne pmd these seem to be working,and leave it mounted to the pump,if you feel you have to relocate the pmd,use the 6ft extension cord and mount it out of the engine bay.air in the fuel seems unlikely these pumps dont tolerate air well and stall,pmd failure is most always stalling , usually hot with the stalling increasing over time untill the engine wont restart. good luck
  12. Philbilly2

    Philbilly2 PlowSite Veteran
    Messages: 3,767

    LOL, I thought I was the only one who kept spare PMD's in the truck! :laughing:
  13. Dewey

    Dewey Senior Member
    Messages: 438

    I have one in my glovebox tooo !!!!!:rolleyes:
  14. serafii

    serafii Senior Member
    Messages: 287

    Is there a way of testing the pmd to see if it's defective?
  15. Philbilly2

    Philbilly2 PlowSite Veteran
    Messages: 3,767

    Change it out with a known good one and see if the truck continues to do what it is doing.
  16. great white

    great white Member
    from Canada
    Messages: 34

    Anyone with a 6.5 who's experienced a PMD failure usually has a spare rolling around.

    One connector and a dead in teh water truck becomes mobile again.

    All of 15 seconds to fix.

    If you have a spare that is....;)
  17. great white

    great white Member
    from Canada
    Messages: 34


    Only way.

    A pmd doesn't set OBDII codes.

    It can cause other codes that may seem unrelated though, like torque convertor clutch slipping....
  18. White Gardens

    White Gardens 2000 Club Member
    Messages: 2,665

    I'm going with the rotted fuel lines.

    My old (though mechanical F-350) diesel would surge and gain RPM's when it started sucking air into the fuel system.

    The long start makes me think it's a fuel delivery problem also. I would get that done first regardless as you need your fuel system in good order anyways and then if you still run into issues, then start throwing money at it.

  19. serafii

    serafii Senior Member
    Messages: 287

    I changed the frame mount pump, the fuel filter and the fuel lines. I don't know what to do next
  20. Joe D

    Joe D Senior Member
    Messages: 605

    It's more than likely the PMD and changing it out even where it is will prove it. If it works then relocate it with the Heath Kit. I have the Heath kit and it's been on a few years now with no issue's.
    I did all new fuel lines on my truck as they were leaking all over the place leaving puddles and filling the valley on the motor. Never had any issue's like your having so I don't think it would have been your issue.