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Fuel in oil (?) and misfiring 7.3

Discussion in '6.9L IH & 7.3L IDI Diesels' started by jonleroy2506, Jan 26, 2021.

  1. jonleroy2506

    jonleroy2506 Full Access Member

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    Hey all,

    I have a 1991 7.3 idi with an ATS turbo on it that has been running pretty rough lately. It's misfiring at all times, especially when idling but I think I can hear/ feel the engine running really rough at highway speeds. The check engine light flashes on and off randomly, and I have noticed that any time the check engine light is on, the oil pressure gauge drops. I realize that in these trucks the oil pressure gauge is just an on/off and doesn't accurately display oil pressure, but it's still got to mean something. I checked the oil yesterday and it is way over full, which would lead me to believe that there is diesel leaking into the oil.

    Just curious what might be causing this issue, or if these couple of issues even sound like they are related
     
  2. Farmer Rock

    Farmer Rock just a fella' without a 10mm socket

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    The diaphram on the lift pump probably ruptured, and started pumping fuel into the crankcase. That is a pretty common problem and would of course cause loss of power since you aren't getting near enough fuel to the IP.



    Rock
     
  3. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    You can smell the oil that's on the dipstick when you pull it out and see if it smells like diesel.
     
    Farmer Rock likes this.
  4. miles1400

    miles1400 Full Access Member

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    is the oil still dark? if it looks like chocolate milk you blew a head gasket.

    i have heard of guys wiping off the dipstick and trying to light it with a lighter. if it lights that means there is diesel in the crankcase.
     
  5. SuperDave

    SuperDave Full Access Member

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    I had an 84 f350/6.9 that had broken both rocker arms on one cylinder so neither valve was opening but since the injector was still spraying fuel it was just going past the rings and into the oil. 2 people couldn't figure it out and the truck was driven like this for quite some time before I owned it and I did a bunch of un needed work before I figured it out including new injectors and injection pump and lift pump. What finally alerted me was the huge dent in the valve cover almost touching the fuel filter so I removed the cover to find the valvetrain in all sorts of disarray. A rocker kit, 2 rocker bolts, 2 pushrods, 2 lifters and an oil change later and it was like new again. I was honestly surprised that no further damage was done as it doesn't take much to hydro lock one of these engines but years later when I rebuilt that one, that particular cylinder didn't look any better or worse than the other 7

    Long story short I'd pull the valve covers and inspect the upper valvetrain
     
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  6. jonleroy2506

    jonleroy2506 Full Access Member

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    Would a failed lift pump cause the misfire? I have a feeling that the issues are related, as the misfire became much worse around the time i noticed the oil pressure drop and the check engine light. Also, how can I know for certain that I have a failed lift pump? If there is no good way, I will likely take it into a shop for diagnostics, rather than throwing parts and time at it in hopes that I make the right guess on what parts to buy. On that note, if I replace the lift pump should I put in another mechanical pump or convert it to electric?
     
  7. Farmer Rock

    Farmer Rock just a fella' without a 10mm socket

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    You will have to remove the lift pump to see if the diaphragm is ruptured or not.



    Rock
     
  8. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    Mechanical or electric is strictly your call.
     
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