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Think my 6.0 is trashed

Blue85

Blue85

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Guys, I need both technical and moral support. I just bought a Suburban and in my first day at home, it picked up a big knock (https://ck5.com/forums/threads/roadtrip-ny-to-mi-06-07-quadrasteer-sub-search.329756/). While changing plugs, a plastic fitting to the heater core broke and gave me a bit of a shower. So my fear is that water got into one of the even # cylinders and it hydrolocked when I started it, even though starting seemed normal. This noise goes away in less than a minute, but when moving the truck, it's obvious that (at least) one of the cylinders isn't firing.


I unbolted the inspection cover and the TC bolts look OK, but I guess you have to pull the starter, front driveshaft and possibly the exhaust to get the cover off. Also, pulling the oil pan requires moving the front crossmember and dropping the front differential. Plugs #6 and #8 look fine. I was going to pull fuel injector connectors to see which one quiets the knock, but it quiets down soon enough I can't be sure.

So help me make logical choices in troubleshooting.

My history with the vehicle is only that it test drove fine and made it home over 500 miles fine, including a cold windy overnight around freezing, after which it started and ran fine.
 
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I had a similar knock in a fat block one time. Was a broken flex plate.

Do have much more to add without knowing more.

I can't imagine the little bit of water that could have gotten in the spark plug hole hydro locking it.
Hope it's something easy!

Don't those 6.0 have a bad history of cold start knocking?
 
my 6.0 knocks everytime when the engine has sat overnight and its colder out...piston slap is what I've read. Once oil gets on the cylinder walls it goes away...usually 15 sec to a minute.
 
Sound is too deep to be a lifter wiping out a lobe on the cam. My bet's on a cracked flexplate. We had one at the shop that sounded like a rod was going to exit the block. Pulled the little inspection shield and looked up in there and saw some clues. We went ahead and pulled the trans to find cracks connecting the holes where the bolts go to the crank. It was 90% broken all the way around.
 
Every single LS built before 2001 or so had cold start knock attributed to piston slap. I just tore a 2000 5.3 apart trying to find a knock and it was piston slap. GM changed it in 01/02 or whenever and it stopped. Nature of the beast. Lucas to the rescue.
 
454Sub said:
Every single LS built before 2001 or so had cold start knock attributed to piston slap. I just tore a 2000 5.3 apart trying to find a knock and it was piston slap. GM changed it in 01/02 or whenever and it stopped. Nature of the beast. Lucas to the rescue.
Click to expand...

I don't think the noise in that video is piston slap. I know that noise well...
 
the sound has an echo and a hollow ring to it. like its hitting a bell housing. I would think more flexplate than piston slap. can you feel anything if you put your hand on the side of the transmission?
 
The other thing I forgot is that I had to chase the threads on spark hole #8. I was careful going in just a couple more revolutions at a time, with anti-seize on the chaser, then backing out to clean it. Was a noticeable amount of shavings, so I kept thinking either I had a chip stuck in the valve seat or the plug just wasn't tight. The plug that came out looked OK.

Thanks for all the input. I'll have to get the inspection cover fully off tonight. Maybe by removing the bolts and pushing the torque converter back I can get see the flexplate well enough.

This is a 2003 truck and is all original as far as I can tell. Was glad to see the inspection cover because my 4L60-E has the 1-piece bellhousing.
 
Not much progress tonight, but at least no exhaust studs broke. The torque converter hardly pushes back, so it's hard to see anything up there. Can't see any cracks - I assume they would be between the crank bolts.

Plan for tomorrow is to reconnect enough stuff to run it with the TC disconnected.

20170410_204319.jpg

20170410_204448.jpg
 
1st thoughts that pop into my head:
It sounds to hollow for lifter/piston
If you shut it off right after the noise stops, how long will it have to sit to make noise again?
Have you used a long screwdriver/stethoscope to pinpoint front/back?
Misfire(or knock retard) only when you hear the noise? Any codes or access to live data?
 
Secure the converter back so the flexplate doesn't interfere with it once it's running
Blue85 said:
Not much progress tonight, but at least no exhaust studs broke. The torque converter hardly pushes back, so it's hard to see anything up there. Can't see any cracks - I assume they would be between the crank bolts.

Plan for tomorrow is to reconnect enough stuff to run it with the TC disconnected.

View attachment 227939

View attachment 227940
Click to expand...
 
I can scan it with torque pro. It's not storing any trouble codes, but I haven't looked at live data while it's happening yet.
 
Ran with TC disconnected and no banging. Still got this strange sound (video below) and them some squeaking which led me to check the accessory belts (Not in the video). Was logging lots of misfires on 5 and 7. Pulled the A.C. compressor belt and it got quiet, almost normal sounding. But logging misfires everywhere, then code 0300 pending (random/multiple cylinder misfire detected.

Possibly some of this is from cleaning the MAF and having the battery disconnected. But I did note a weird pulsing when pulling it into the garage, like 1 or more cylinder was dead.


(Wow I need to clean the garage).
 
Blue85 said:
Ran with TC disconnected and no banging. Still got this strange sound (video below) and them some squeaking which led me to check the accessory belts (Not in the video). Was logging lots of misfires on 5 and 7. Pulled the A.C. compressor belt and it got quiet, almost normal sounding. But logging misfires everywhere, then code 0300 pending (random/multiple cylinder misfire detected.

Possibly some of this is from cleaning the MAF and having the battery disconnected. But I did note a weird pulsing when pulling it into the garage, like 1 or more cylinder was dead.


(Wow I need to clean the garage).
Click to expand...

That does sound better. Did you get any closer look at the flex plate?
 
I guess I should put the bolts back in to see if the noise comes back. I can't see anything more up there without pulling the engine or tranny.
 
Idling the fuel trims have settled to -3.9. Fuel pressure is 55. Misfires stop at any speed above idle. Idle is OK, but not perfectly smooth. I noted that when I test drove it, though.

 
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