Cat C15-6nz pinging sound rough idle

Discussion in 'Kenworth Forum' started by Ttimefr, Sep 1, 2022.

  1. Ttimefr

    Ttimefr Bobtail Member

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    Apr 20, 2022
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    Evening guys! I have a problem that nobody can seem to figure out I’ve been to many different mechanics and Ive made a post before but didn’t get any good response so I’m trying again. I’ve got a 06 T800 with a MXS that I overhauled and converted to a 6nz. C15 block and 6nz from the head up. The setup started off with full tilt manifold 80mm none waist gated turbo 800 marine cam 8501 injectors 70 pin ecm and yes not knowing any better it was left with 18.1 pistons. It ran great for about 6 months then pulling up to fuel up during a hot day in SC I noticed it ideling really bad. It kinda came and went for a while till it started getting worse. Took it to a mechanic and said it was injector number 2. Replaced it and did somewhat better but after mid day when things got hot same problem. Ended up with all new injectors again and same problem. Tried different files and swapped ecm same thing. Suspected it was air since my fuel hoses were in rough shape. Got new hoses every single one of ‘em honed out injector bored installed fass fuel pump and cat transfer pump with upgraded spring kit and filter housing blocked off hand primer no change. Talking to ppl we decided go get rid if the cam and go stock and got another set of Delphi 8501 injectors. After that the idle was better but if I bumped it up to 1000 rpm sounded like ####. We’ve checked gear lash redone wiring harnesses sensors checked all the wiring redone battery leads and solenoids and circuit breakers im at a dead end. I’ve checked for air leaks replaced manifold gaskets cuz I had a stud break new air to air new turbo and gaskets since the first one started pushing oil to intake side nothing helps. I’ve been running it for over a year now it has plenty power has a little blowby but doesn’t use any oil between changes. Don’t use any coolant all fluids look look like they should. I’ll idle it up to 1000 and go to bed if will shake the sleeper like no other and when I wake up it’ll be running reall smooth. It all seems to be intermittent depending on the day. Some days it pulls reall smoothe and other days I lay on the gas and it sounds like a chirp when it is under boost and next hill it will be just fine. It has a pinging noise that you hear all over especially through exhaust. Like if you were to tap a coffee mug with a spoon. It’s impossible to do a cut out test cuz you’ll think it’s number 1 then number 3 then another and so on. It’s almost like bad timing and it doesn’t have a single logged code and has never been overheated. Also my Jakes started to act weak lately but work on all 3 stages but sometimes seems like they don’t shut off when I come to a stop I’ll pull out out of gear and it gets a extra pop and worse on colder mornings. I have around 250k miles on it now and keep running but it’s driving me nuts. I greatly appreciate any advice y’all can find me.
     
    Last edited: Sep 1, 2022
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  3. spsauerland

    spsauerland Road Train Member

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    Have you replaced fuel hoses including return hoses?
     
  4. Ttimefr

    Ttimefr Bobtail Member

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    Apr 20, 2022
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    Yes every single hose, fitting, divider valve check valves pickup tubes all of it
     
  5. spsauerland

    spsauerland Road Train Member

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    You do realize your piston bowls and injectors do not match correctly?
     
    Roger McG and ProfessionalNoticer Thank this.
  6. Ttimefr

    Ttimefr Bobtail Member

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    Apr 20, 2022
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    Are you saying I needed to get a 16.1 compression pack? Yes I didn’t know that at the time and my mechanic evidently didn’t know what he was doing either. I just told him to over haul it and get rid of the twins. That is also why I got rid of the marine cam the only way to make it work was a bigger injector and it’s already a time bomb as it is. That being said if the injector angle didn’t watch the bowl why did it run as good as can be for a while. Shouldn’t that just not work from the get go? Also used to work on a farm had several of those engines low miles never overhauled just got rid of the twins same acert pistons and they run great
     
  7. Ttimefr

    Ttimefr Bobtail Member

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    Apr 20, 2022
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    Is there a injector that will make this run or is it a done screwed up waist of money. I feel like running it blows more than spending more money on it. My question is if that’s the case then why did it run great for about 6 months what would have changed
     
  8. spsauerland

    spsauerland Road Train Member

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    First off, I don't consider myself an expert in this subject and I will just state my opinions based on the facts that I do know.
    You built a Frankenstein and it is still a hybrid of a C15/C-15. The 18:1 compression works for awhile, but eventually weakest link is found as in usually HG or cracked head. The most misunderstood thing about the ACERT was it was miller cycle engine, not traditional otto cycle. So during light engine loads, the VVA's we're not actuated and your effective compression ratio was higher vs during heavy engine loads when actuators delayed the closing of the intake valve and stuffed in cooler dense air with lower effective compression ratio because piston traveled farther up when compression stroke starts. Piston bowls are a subject matter all in their own. The design shape greatly effects fuel air mixing, swirl, quench, emissions output etc. Subtle changes greatly changes combustion dynamics. Everything is a trade off in the designs. Best policy is just to match your piston bowls to the nozzles that factory used and up your nozzle flow while keeping same nozzle geometry (whole other topic books are written about). I could go on, but theories don't fix your truck. My first question is did you examine the injector seats when you replaced them? I would be checking for the possibility of combustion gas getting into your fuel.
     
  9. Ttimefr

    Ttimefr Bobtail Member

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    Apr 20, 2022
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  10. Ttimefr

    Ttimefr Bobtail Member

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    Well this was a expensive lesson to learn. Thanks for everybody’s input I think y’all all correct most mechanics can’t believe I managed to make it last as long as it did considering the time bomb it is and the HP it was putting out initially. After having many ppl look at it I figured I’d take one last look myself. Pulled all the rockers of the shaft inspected them 1 by 1 turned out injector rocker 1 and 2 almost have the bushings ate out of them. At this point I think the cam still looks ok. Since almost everything is still new I’ve decided to just buy the right pistons and sleeves and just do a simply inframe on it and save what’s left over here. I wouldn’t be suprised if the gasket is shot between firing rings somewhere and I’m hoping my head ain’t cracked yet. And to answer your question yes I bought the tools and reamed out the injector bores I ding have any combustion in the returned fuel. That being said can I get by with getting new rocker shafts and just rebush my rockers? Also what are my chances of my liners being sunk? I’m hoping not having to counter bore again as it was done at the time of the making of this time bomb
     
    Last edited: Sep 13, 2022
    spsauerland Thanks this.
  11. Oxbow

    Oxbow Road Train Member

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    Very well said. Nice explanation of ACERT technology and the function of VVAs.
     
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