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7.3L Rough Idle/Knock, White Smoke when Cold, Loss of Power

10928 Views 17 Replies 4 Participants Last post by  cjayl1
-Rough idle/distinct knock that is worse when engine is cold
-Lots of white smoke on cold start (unplugged)
-Some white smoke when plugged in​
-Strong smell of diesel at all times
-Loss of power
-Terrible fuel mileage

1) Excursion was filled with gasoline accidentally
2) Excursion was taken to diesel shop who put in:
-New OEM injectors​
-Fuel filter​
-Blew out all fuel lines​
-All new glow plugs (unrelated to gas incident)​
3) The truck ran great for a few days, but I ran it low on fuel to clear any gas left in the system, which led to it stalling
4) I filled it with diesel and it started fine, but idled slightly rough
-Also had battery light come on intermittently​
5) I replaced the alternator after having it confirmed to be bad
-No change in idle​
6) I drove the Excursion for months and the idle progressively got worse
7) I did research and found that the ICP could be the cause
-ICP had oil in connector (meaning bad), so it was replaced with OEM ICP and pigtail​
-This quieted the idle, but the knock was still obvious​
Throughout this time, the truck would smoke white at first startup of the day and smell strongly of diesel
-Lots of smoke if unplugged, until warm​
-Less if plugged in, but still some initially​
8) CPS was replaced with BWD one from O'Reilly, as it is a simple and cheap thing to try
-This made the engine run terribly, so I thought I got a bad CPS​
9) Got another replacement BWD CPS and installed it
-Made it run terribly again, so re-installed OEM one​

So, this is where I am now. I have a rough idle and distinct, rhythmic knock that is worse sometimes than others, but consistently gets better as the engine warms up. I have white smoke on start. I can smell diesel at all times if I'm outside of the cab. I'm getting horrible fuel mileage and have a loss of power.

-Freshly changed oil/oil filter
-Have an oil leak that I can't trace, but always keep it topped off
-I have a TS Performance 6-pos. chip installed
-I do not have access to a scan tool with live data

Does anybody have suggestions on what to check next?
Could there be other things that the gas could have damaged that weren't replaced?
Does anybody know why it would run substantially worse with a new CPS?
-Could a new CPS amplify an existing problem?​
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The engine was run with gasoline for about 10 miles. The truck slowly started to run worse and worse as the fuel became more concentrated with gas rather than diesel. I didn't know that gas had been put in it. The shop that did the work on it did do a compression test, which they said checked out. I don't know if that tells you anything about melted pistons. But another notable thing is that after the work was done, it ran perfectly smooth until it ran out of fuel, making me think that there probably were no huge mechanical issues in the cylinders, but I am not certain.
Yeah, I know. I wish I knew somebody with a scan tool. And yeah, all new OEM injectors.
That would be extremely nice! I live in Fort Collins, Colorado.
Pop your oil fill cap while its running. Does it have a lot of blow by? If so you have a washed/dusted cylinder which would explain your knock.
I'll check the blow by, but how much is a lot? If you unscrew it completely and the cap stay in the hole, is that good, or how do you judge?
Okay, thanks. I'll try that. Do you happen to know what good compression test numbers are on these motors?
I just tried flipping the cap on the oil fill tube and it did not lift off at all. It vibrated from side to side, but no lifting.
I agree with ^^^. Also to the OP was the mechanic who fixed it a reputable diesel mechanic?
Yes, the shop I had the work done at is the largest independent diesel shop in northern Colorado... however, I don't know how much that means because I was not satisfied with their service.

I did some looking around by the fuel bowl and I definitely have a fuel leak. I touched the back of the fuel bowl, my hand got wet and smelled like diesel. I believe it is coming from the fuel filter cap because the fuel bowl is slightly dusty on the outside, except for the entire back side, from immediately below the cap all the way down. It's clean like the fuel has been leaking from under the cap and cleaned the dust off. While the truck was running, I looked at the back of the fuel bowl and couldn't visibly see it leaking, so it must be a pretty slow leak. Every time I park somewhere, there is at least a 5" diameter spot that looks like oil below my truck. After finding this leak, I now realize that it is actually fuel that runs down the valley and picks up some old oil along the way, making it dark like oil. After consistently parking on my driveway, there is a huge spot on the concrete (about 3' x 3'), and it is much lighter in color towards the outside, like it's fuel, not oil. I don't know why I didn't think of it before.

Is it possible that such a slow leak from the fuel bowl could be creating spots like that everywhere I go, or is it more probable that I also have another fuel leak from somewhere else, also?

Also, could a leak from the fuel bowl be causing all of my issues: rough idle/knock, terrible fuel mileage, and white smoke on cold start?

Btw, thanks a lot for helping me through this!!!
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