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GMC Brigadier Cummins wont rev just idles

Discussion in 'All Other Diesels' started by schiker, Jun 9, 2016.

  1. schiker

    schiker Well-Known Member

    2,268
    308
    Nov 9, 2008
    Pendleton, SC
    My neighbor has a GMC Brigadier with 1981 Cummins 300HP engine he uses as a farm truck water buffalo to wet his arena. It will crank up and idle but won't rev up. The fuel rod from pedal moves and rotates an arm on the IP but no change in rpm.

    Is there a rack or something that sitcks or gums up that I can get to while the IP is on the truck try and wiggle it or squirt it with some cleaner.

    As a side note he ran it out of fuel the other day. When I got there he was running it on ether a squirt here and there. He had filled the fuel filter up then started it on ether and kept it running until it purged itself. But that seems wrong. Is there a way to bleed the air after filter change? All I see is a water drain on filter and no lift pump inline between tank and IP ???

    I see a brass cap thingy that looks interesting on top of IP on a part that sticks up on the IP but he said he didn't know what it did. I think he took the pipe plug out of top of IP (flat top) and filled it up to get air out????

    Any suggestions that might be easy to try or is there a problem internal to the IP that is beyond shade tree field work?

    Sorry the picture is rotated I thought I had resaved it straight so will post another copy in next post.
     

    Attached Files:

  2. schiker

    schiker Well-Known Member

    2,268
    308
    Nov 9, 2008
    Pendleton, SC
    Dang windows 10. 3rd try might be right.
     

    Attached Files:

  3. 79jasper

    79jasper Active Member

    240
    102
    Nov 10, 2013
    El Paso, TX
    I believe that's a bleeder valve.
    I would be surprised if there's not a hand primer on it somewhere.

    Sent from my SAMSUNG-SM-G935A using Tapatalk
     
  4. schiker

    schiker Well-Known Member

    2,268
    308
    Nov 9, 2008
    Pendleton, SC
    I don't see any pump electric, hand, primer bulb or other. I see the hose that connects saddle tanks and hose that runs from tank to filter head inlet. I crawled underneath and see almost entire length of hoses. I possibly could have missed it but don't think so. The filter is a big truck style flat filter head hose in and out water drain on bottom of filter canister. I can see taking the plug out on top of IP and filling it with fuel to get most of the air out enough to get it to run and purge itself if not bad air locked seems to have worked for him.

    Just totally guessing is that an idle adjustment screw on the front side of IP left of the brass cap? And a fuel shut off mechanism on top of IP like it shuts off the return flow and chokes IP internal? When you turn the key off it runs out of fuel like it starves not a sudden shut down like an inlet fuel shutoff.

    On the bleed brass cap if no primer pump or lift pump would you crank with the brass cap loose let it spit and purge and close it while cranking to purge last of air?

    Could I unscrew that brass cap or front screw squirt some ATF or other solvent in there and work something loose to help free flow the fuel so it can rev up? OR blow out what look like return lines. The truck is rough so it could be something simple. I just don't know and don't think he does either.

    Or is it not advisable to turn that screw might be hard to reset it? Is it a stop for a rack or governor rod or something ?????
     
    Last edited: Jun 9, 2016
  5. GM Guy

    GM Guy Manual Trans. 2WD Enthusiast

    4,632
    398
    May 6, 2008
    NW Kansas and SC Idaho
    The Cummins PT system is like nothing else out there, sort of a mechanical common rail setup, alot lower pressure.

    I think the one little thumb screw disables the fuel shutoff, and might be part of the issue.

    I dont know enough to be of much help, but I am afraid too much has been tinkered with, and its time to find oneone who knows the old Cummins PT system.
     
  6. schiker

    schiker Well-Known Member

    2,268
    308
    Nov 9, 2008
    Pendleton, SC
    Yeah, it is Greek looking compared to everything I have seen.

    He is having a hard time finding someone that knows the PT system that will make a house call. Not worth it to him to tow/haul if its going to cost a bunch to fix/tow it even if there is a local shop that knows it.

    I watched some of a video on youtube. It is way different than a distributor type IP that runs individually to injectors. I haven't watched enough to figure out what triggers the injectors but it doesn't seem to be this part of the IP system. The PT IP appears to be able to operate without a lift pump. The fuel shut off is after at least one stage of pumping and somehow chokes the metering internal to the IP???
     

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