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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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1 - 7 of 18 Posts
how long did you run it with gas? It could have melted your pistons....
Well without a scan tool you can only do so much. The mechanic put in new injectors?
Yeah, I know. I wish I knew somebody with a scan tool. And yeah, all new OEM injectors.
Where are you located? There might be an org member near you who would help you.
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?
Turn the cap upside down, put it on top the hole and if it blows off theres a good chance that your motors dusted.
Okay, thanks. I'll try that. Do you happen to know what good compression test numbers are on these motors?
Off the top of my head I think cranking compression is supposed to be around 400 psi, cant remember for sure.
Maybe you still have some gas in the system? Water?

Sent from App
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!!!
No problem. If you do have a fuel leak that lets air get in the fuel system it could cause a lot of running issues. I would start by changing the fuel filter, it probably needs to be changed anyway after gas was ran through it. I would fill the bowl with fuel after I took the old filter out. If it still leaks you can get a mirror, start the truck, and use the mirror to find your leak. Depending on where the leak is it might just be causing the truck to lose fuel pressure and actually not be letting air in.
1 - 7 of 18 Posts
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