cat 3126

Mechanics Hub Forums Diesel Engines CAT cat 3126

This topic contains 12 replies, has 7 voices, and was last updated by  James 1 year, 6 months ago.

Viewing 14 posts - 1 through 14 (of 14 total)
  • Author
  • #25483 Reply


    i got a engine that starts hard some times cat 3126 …… codes .but think there fuel getting the coolant .
    sounds like injector cups to me …….any think i should try be for i get in to the injector cups and what tool do i need to pull the cups

    #29138 Reply

    Hey Chad! I seem to recall a similar issue once. We were going to condemn the ECM on that one. That’s a HEUI, isn’t it?

    #29139 Reply


    HEUI yup

    #29140 Reply

    Ya. Is there no way to get codes there?

    #29141 Reply

    John Whelan

    Chad, We had a hard start problem and it was the injector O-rings. Have a look at them first. Could you get an oil sample test done to see if the engine oil is contaminated?

    #29142 Reply


    yup no problem to get a oil sample done . ill take a sample and seen it out Monday

    #29143 Reply

    John Whelan

    Chad, Let us know if you find anything. We use oil samples for our fleet and it is very detailed with coolant, metal and fuel indicators among many other tests. It used to cost $17.00 per sample but now we get them for free through our bulk oil supplier. If you have a Castrol oil salesman coming around ask them about it. You get a credit for every liter or quart of oil you buy which goes towards shop equipment they provide like bulk oil dispensers or grease pumps etc. Once you sign up oil samples are free as well. They provide the sample bottles and pre-paid shipping to the test lab.

    3126 blog post on failed o-rings

    Bad injector seal possibilities….Depending on what o-ring fails Bottom o-ring… It could fill the cooling system with fuel (with leaking seat problem) and push coolant/fuel out the overflow tank. Middle o-ring..check your fuel tanks and see if the fuel is a black color from high pressure oil going to fuel return to the tank. High pressure oil could also re-route out and around the head if the top o-ring fails losing high pressure oil pump pressure.

    #29144 Reply

    Hi Chad,
    My opinion: injector sleeve or injector sleeve seal. Try this:
    1.Remove the valve mechanism cover and all the injectors
    2.Clean the injector places in the cil head
    3.Pressurize the cooling system in order to identify the injector sleeve that is leaking. (15-17 psi max)
    4.Closely inspect the sealing joint around the top of the injector sleeve. (Small amounts of coolant will be dripping from the injector sleeve that is leaking)
    After the engine shutdown, the retention of pressure in the cooling sistem may couse the transfer of coolant in fuel sistem. Visualy inspect the fule tank for coolant.
    Good Luck

    #29145 Reply

    Aren’t these forums great?! There’s nothing like talking to a guy who says”I’ve seen that before”. Saves mountains of time.

    #29146 Reply

    John Whelan

    Forums ARE invaluable! Especially when you consider the years of experience hanging around here. I love to save time…..when someone has already been through a problem and shares their knowledge it’s a big bonus 🙂

    #29148 Reply


    Chad, you will need a special puller from CAT to remove the injector cups. You will also have to replace them as the removal process damages the cups. There are many things that can cause a hard to start condition with a HEUI engine but if you have fuel in the coolant it is a good place to start. Follow Joseph’s instructions and get back to us. I can provide you with the part number of the removal tool and any sealants/procedures that you may need if indeed this is the repair you are doing.

    #29149 Reply

    Hi everyone!
    Yes, it is very wide spread problem on that engines.
    1. Remove all injectors.
    2. Change injectors seals.
    3. Remove all injector sleeves.
    4. Clean seating place for sleeves.
    5. Install all new sleeves and seals.
    6. Install injectors with new seals.

    If you have hard start sometime, check by Electronic Technician an oil activation pressure, if not ok – change HEUI oil pump. If pressure is ok, check fuel pressure (must be about 500kpa) and check fuel pressure valve. If valve is ok, may be you need to change fuel transfer pump.

    #47656 Reply


    Please can you advise if the voltage from the ECM to the injectors on a Cat 3126 will show on a Fluke Volt Alert pencil unit – mine seems to be for AC voltages only and not sure if it will pick up any signal from the ECM on this 3126 Cat engine?

    #50688 Reply


    injectors take over 100 volts to fire. a noncontact voltage detector will work

Viewing 14 posts - 1 through 14 (of 14 total)
Reply To: cat 3126
Your information: