379 sputters at idle when loaded

Discussion in 'Peterbilt Forum' started by Palo379, Jun 27, 2022.

  1. Palo379

    Palo379 Bobtail Member

    3
    0
    Jun 27, 2022
    0
    So I’ve been fighting with this the past week, I got a 1994 peterbilt 379 dump truck with a 3406b. Top end has been rebuilt about a year ago and has only been driven once in the last 6-8 months before I started driving it last week. So to begin with, oil pressure is lower than what it should be but I’m still in minimum specs which is 25psi. But this is the weird part, when I get loaded to 54k pounds, let me remind you I’m still under the loading bay and haven’t moved or anything trucks still in neutral and all. As soon as I get loaded, my truck starts sputtering, rpm’s drop below 5 and oil pressure drops below 20 and just bounces around there but goes away and acts fine when I get on the accelerator. Hooked up a mechanical gauge and it reads the same. I do have a leak in the airbags on my drives, also my bags don’t air up until I start driving even if my pressure is built up all the way. But I’m not sure if that has anything to do with my oil psi and rpm’s dropping when I get loaded. It just doesn’t make sense to me, it only does this immediately after I get loaded but it’s perfectly fine when I’m not loaded. Oil and filters been changed along with fuel filters too. Neither was contaminated. It only does this at idle
     
  2. Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.

  3. Palo379

    Palo379 Bobtail Member

    3
    0
    Jun 27, 2022
    0
    Also want to mention I have other trucks that run about the same oil pressure but they don’t sputter when loaded
     
  4. baha

    baha Road Train Member

    4,055
    2,705
    Jul 25, 2013
    ga
    0
    1st ck the ground connections from motor to the frame, and cab to the frame! But alot of them run the other main ground from starter ground pole with alot of other big wires under it, the wires from batt. should be closest to starter then the wire to frame, funny things can happen with the gauges with a bad ground wire to dash, but the wire leading to the fuel cut off on the motor needs to be ck for green corr. On it.?
     
  5. lester

    lester Road Train Member

    2,205
    5,387
    Jan 2, 2012
    NW, Iowa
    0
    When you get loaded is something sagging that would be pushing or pulling on your throttle linkage? I don't imagine it's an air ride cab but it's possible. Definitely an odd problem but has to be something to do with the weight in the box changing something.
    Something mechanical, nit much electronic on a B model. Other than fuel solenoid
     
    Roger McG and Catmando Thank this.
  6. Catmando

    Catmando Road Train Member

    3,132
    13,018
    Mar 15, 2021
    Iowa
    0
    Could very well have a broken or bad cab mount
    I agree there's nothing really electrical on the fuel system on a B model other than the fuel solenoid and its either on or off
     
    Roger McG Thanks this.
  7. SmallPackage

    SmallPackage Road Train Member

    3,335
    9,803
    Dec 20, 2019
    Marion Texas
    0
    Is this a straight truck? If so. Maybe getting a little frame sag from 54k constantly being dropped in the box. Causing the throttle linkage rod to change position a hair or two between engine and cab movement.
     
    Catmando Thanks this.
  • Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.

  • Draft saved Draft deleted