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2012 F-250 6.7L - Engine Knock Under Load Only

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Old 01-02-2018, 03:43 PM
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2012 F-250 6.7L - Engine Knock Under Load Only

I am looking for help help to determine what might be the cause of an engine knock that I have in my truck,

2012 F250 KR
6.7L Powerstroke
73,000 miles

The truck took some water into the air intake during a Hurricane Harvey flood rescue back in August and at one point, it did stall. I was able to get it running again and drive out of the water. It sputtered a bit but then did finally line out and sounded normal but this was with torrential rainfall and 60+mph winds so I could not hear the engine all that well. Most importantly, we were able to complete the rescue. It did throw a couple of codes related to the exhaust fluid system and those codes have yet to be addressed.

It sounds normal at idle and does not knock when accelerating the engine while in Park or Neutral. There is a noticeable knock that does occur during acceleration while driving down the road.

I don't think it is a lower end problem as I would expect it to knock all of the time. Any idea what this might be?

I have not been driving the truck. It's sitting in a warehouse waiting on me to address this.

Any and all help is appreciated.

Thanks,
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Old 01-02-2018, 03:53 PM
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I should also note, it does not seem to have any sort of power loss and it starts right up with no problem. It's been driven at least 100 miles since this occurred.
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Old 01-02-2018, 04:12 PM
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I have seen this before with a bent piston/connecting rod, not bent enough to actually hit anything but the air/fuel mix is not fully compressing causing a late detonation. It may be injector hammering also. If water got into the cylinder, which sounds like it did, I would bet on a bent piston rod.

With an SCR/DEF its hard to tell if there is any smoke, but you should have some black smoke also
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Old 01-02-2018, 06:12 PM
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No smoke. Exhaust is clean.
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Old 01-02-2018, 10:15 PM
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The DPF scrubs any useful indicators from the exhaust these days and isn't as useful as years past.
My money is on a tweaked rod. A cylinder contribution test may help, but I'd recommend a full compression test.
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Old 01-12-2018, 01:59 PM
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I am betting a bent rod also. I fixed quite a few gas engines over the years that didn't throw the rod out the side of the block.(Those got new short blocks) Some still ran but just knocked.Physics apply!! Fluids do not compress!! Can usually tell with compression test, then measuring deck height of pistons with heads removed to verify how many rods are shorter than normal.
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