6.9 idi, no power, but starts perfect and no smoke.

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Tim Y, Nov 13, 2017.

  1. Tim Y

    Tim Y Registered User

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    I've been searching for months now, and can't seem to come up with a similar problem. My truck has a 6.9 with just under 100k miles on it. It starts and idles perfect, even on cold days, or after sitting for weeks. Under slight throttle and when up to speed it runs just fine. If you put a load on it or floor it, it barley moves, but it doesnt blow smoke at all. I feel like the extra fuel isnt coming in as it should. I checked and the throttle cable isnt stretched, and when you floor it you can feel the transmission holding gear longer, so I'm sure the throttle is moving properly. I'm leaning towards need and injection pump, but I wanted to hear some other opinions first. Other descriptions that i hear are, hard starting, rough idle, blowing smoke, and I'm just not having any of those issues. Anything past just slight throttle and the truck just has no power.
    Thanks in advance,
    Tim Y
     
  2. Thewespaul

    Thewespaul Supporting Member Supporting Member

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    Welcome to the forum Tim, have you tried replacing the fuel filter? Do you have fuel spraying out of the schrader valve when the truck is running? Does it surge when you step on it while driving?
     
  3. Tim Y

    Tim Y Registered User

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    Thanks for the welcome. I've replaced the fuel filter twice at this point, both times with some diesel kleen in it. Haven't checked at the schrader yet, and there is no surge. Take off from a light, and anything beyond light throttle to full throttle is no change, loses steam with a load or going uphill and takes forever to get up to speed. It wasn't like this when I first got the truck, and has progressively gotten worse.
     
  4. Thewespaul

    Thewespaul Supporting Member Supporting Member

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    Surging would be a sign of air intrusion so that kinda rules that out, does it do it with a full tank? Could be a weak lift pump
     
  5. Tim Y

    Tim Y Registered User

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    I've thought about the lift pump. I really need to check pressures on the truck. I've thought about going to an electric lift pump as well. I haven't had a full tank in it, but its the same at half a tank or really low. In the future I'm going to drop both tanks, the front sender quit working and the rear tank has some issues with venting. It has the same issue on the front or rear tank as well.
     
  6. sjwelds

    sjwelds Full Access Member

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    Hmm. If the tanks aren't venting properly you could be sucking a vacuum. Sure sounds to me like a fuel restriction/vent problem/weak or failed lift pump.

    Take the fuel cap off and drive it, see if anything is different.
     
  7. Tim Y

    Tim Y Registered User

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    Now that you mention it, someone stole both of my fuel caps while the truck was parked out front. The front tank is the same as always, the rear tank actually sprays fuel out of the filler neck.
     
  8. Macrobb

    Macrobb Full Access Member

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    You've probably got a bit of the "cone of failure" in the fuel line somewhere. I'd suggest blowing the line back with compressed air from the rubber hose on the lift pump back.
     
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  9. Trevtron

    Trevtron Supporting Member Supporting Member

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    Definitely take the advice of the members here, start with the simple stuff in sequence.

    I’m not an expert, but after reading what is happening to you it reminded me of how my truck had similar symptoms, turned out it was the IP. My truck would fire up and idle perfectly with the bad IP and when I gave it more than 1/8 throttle it would not respond.

    Got a new IP and injectors and life is good
     
  10. Knuckledragger

    Knuckledragger blowing chunks

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    Sound like an obstruction if there is no surging or quitting. In a gas car, this would scream, "cracked fuel line", but diesels react differently to air intrusion.

    Start by checking the fuel lines that are easy to find and clear. The age of the truck dictates that if you have never had a shower head failure, you now have one. They disintegrate and can get pieces throughout the fuel system, sometimes ruining the tank selector switch. Don't ask how I know.
     
  11. frankenwrench

    frankenwrench overkill is under rated!

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    Just figured out about that showrr head failure..... Still not pleased about it. Plummed directly to my bulk tank for my pickup and return with a bit of my own design and disregarding problem all together. No longer have tanks under my truck anymore
     

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