3406E With a stumble/miss - sometimes

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by WHY NOT, Feb 24, 2021.

  1. WHY NOT

    WHY NOT Light Load Member

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    Oct 18, 2015
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    6TS 3406E and I just got done replacing all the injectors in. New fuel filters, and I can still feel a vibration sometimes under partial throttle about 1400-1500rpm. Over head was ran when we did the injectors.

    I left the house the morning and made it to my destination about an hour or so away and the truck ran absolutely perfect. Sat in the grain line for about 3-3.5hrs and idled the truck up to 900rpm while sitting still. By the time I left the truck was running rough under partial throttle with the vibration. It has a tick to it when it starts acting up, the sound reminds me of an exhaust leak kind of sound but I cannot find soot anywhere.

    Any ideas of what and how to check would really be appreciated. Ive been banging my head on the steering wheel chasing this problem for far to long.
     
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  3. zinita17601

    zinita17601 Road Train Member

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    Did you check your fuel pressure?
     
  4. Don379

    Don379 Light Load Member

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    Jan 7, 2021
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    ah man, tough one. Check fuel pressures with long enough hose and gauge so you can read it in the truck and see what it looks like while this is happening? This is to rule out the obvious. After that, i would be pulling the valve covers and checking the valve cleances myself. I dont trust shops with that stuff. Could be an injector on its last leg too. So i would be digging into that if the first 2 suggestions were ok.
     
  5. WHY NOT

    WHY NOT Light Load Member

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    Sounds good, my mechanic is an independent and is pretty good with CAT's but actually thought and had me run the overhead. Like I said the injectors are all new, but I've heard of stranger things than a new part thats bad. I will get a gage on it first. Thanks for the help. Dang thing is just frustrating.

    I did forget to mention I am NOT down on power at all
     
    Last edited: Feb 24, 2021
  6. Don379

    Don379 Light Load Member

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    yeah. i would be curious to see what the gauge doing when this happens.
     
    BoxCarKidd Thanks this.
  7. E model Cat man

    E model Cat man Light Load Member

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    Jun 10, 2014
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    Did it have the same issue befor replacing the injectors? If i had to guess id say an injector plunger is sticking and not returning to the top of its stroke and every time the injector rocker is starting to open and makes contact again it causes a tick...thats the only intermittant problem that i can think of that would be accompanied with a tick. Excessiveley hot fuel could actually cause this problem i mentioned...excessiveley hot fuel is usually caused by a restricted fuel return line or a regulator check valve thats stuck in the closed position not allowing any fuel to return and when this happens their isnt any fresh/cool fuel circulating threw the head to cool the injectors...when the system is functioning properly their is around 4 times as much fuel circulating threw the head every minute than the motor use...the cool fuel not only makes more hp but it also helps cool the injectors and keep their internal running clearances in spec...if they overheat the plungers can stick, needles can stick. Etc..you need to put a pressure guage on it at the compucheck fitting thats located at the fuel distribution block right behind the air compressor. If you have more than 120psi and like 140+ that would be a dead giveaway that the pump is deadheading and not returning ang fuel...just some fuel for thought i guess.
     
    black_dog106 and WHY NOT Thank this.
  8. WHY NOT

    WHY NOT Light Load Member

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    Perfect thank you. I still need to get a pressure gauge on the thing, Been stupid busy. But yes it had the vibration/ stumble before the injectors but can't recall the tick as much. All great suggestions and will look into them.
     
  9. WHY NOT

    WHY NOT Light Load Member

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    @E model Cat man I went ahead and replaced the check valve on the fuel block being the compressor and no change. When I was down to 1/3 tank or so of fuel I can hear the fuel returning into the tanks with the caps off, sounds like you're taking a leak in a puddle so Im guessing that it is returning fuel alright. But I still need to get a gauge on it. Just curious what ports to use to check the supply and return pressure and where the pressures should be at. IMG_5029.jpg
    the check valve I replaced was the one on the bottom that takes a 1" wrench, hopefully that was the correct one. Also what kind of threads do I need for the pressure gauge to hook to this thing, do you us an adaptor or is there one that can be hooked straight to it.
     
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