C6500 with Cat 3126 Idle/Cold Start Issue

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by paul'sconcreteinc, Mar 23, 2021.

  1. haycarter

    haycarter Road Train Member

    Jun 9, 2012
    Aren't the 3126 Injectors Hydraulically actuated as apposed to camshaft actuated like the 3406 ect??

    OP those motors need CLEAN oil to work properly..
    Extended service intervals & sludgy Oil will cause havoc with that fuel system...!!
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  3. ClineER

    ClineER Light Load Member

    Apr 27, 2016
    N.E. Oklahoma
    I've had a similiar issue on reman injectors, more money but I would only go Cat parts on it, have had other remains miss right away. Another problem is injector connectors get brittle, and he may of broke 1 or 2 and can cause a misfire, if the plastic is cracked, replace the end.
    Otherwise, has he gone on test drive since install? With air in oil system they can misfire and carry on till all air is out of oil passage in head.
  4. SmallPackage

    SmallPackage Road Train Member

    Dec 20, 2019
    Marion Texas
    I have had a ‘99 3126B baby Cat since new. The HEUI fuel system is the problem. Like was said above the injectors are hydraulically activated by engine oil that has the psi raised by the fuel pump from the 25-70 psi range up to around 20,000 psi. Clean oil is imparative. Mine always started to idle rough around 8,000 miles on the oil telling me it’s time to change it.

    The HEUl fuel systems of that vintage are very finicky and prone to failure. Internals wear out. When they do they allow metal shavings and pieces to go straight to the injectors destroying them. They updated the design in 2002-3 time frame with the 3126E and the early issues were fixed.

    I also had no luck just replacing one or two injectors at a time. Seemed like the others would fall in line and fail really soon after. Best to do them all at same time. They have exchange core program because Cat remans them.

    Also just something to think about. Holt/ Cat who I use for this type of work has always had mechanics that were trained to ONLY work on this engine. It is different than the big ones.
  5. Inderjit

    Inderjit Light Load Member

    Sep 17, 2017
    I replaced the injectors and high pressure pump in a 3126 last summer. The complaint
    was a misfire when the engine was hot. The engine was in a Freightliner M2 so the valve
    cover was easy to remove, no piping in the way. I don't recall how long it took me but I
    started at 8:00 in the morning and it was done before I went home after a 7.5 hour shift.

    The pump and injectors came as a kit from Caterpillar. The sub dealer ship I work for
    were advised to replace the pump because of the high hours on the engine the pump
    was probably failing and metal particles from the pump were causing the injector problem.
    nine or ten months later its still going strong.
    BoxCarKidd and baha Thank this.
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