This is not a swap question, it's a problem with an actual truck so I understand if it shouldn't be posted here and this thread is removed. I just thought I'd give it a shot.

I just acquired a 2004 2500hd with a 6.0. The truck is old but it only has 6900 miles on it (yes 6,900 not 69,000) so it's done a lot of sitting. The owner used it for her horse trailer and I know she hasn't had horses in a couple years but she said she had driven it in the last year. I cleaned a huge mouse nest out of the air box and put in a new battery, oil and filter.

The problem it's having is a very rough idle and loud knocking noise. I am getting a P0300 misfire code. I am suspecting a collapsed lifter. I haven't had a chance to dig any deeper yet, hopefully I will this weekend, weather permitting. I just wanted to get some opinions of others who might be a little more familiar with these engines on their suspicions.

It runs so poorly right now and sounds so bad that I don't even want to let it run to try and check fuel trim and vacuum and stuff. But if there's major damage the damage is done so I may as well do all the tests I can. I am a little worried about damaging the cat still. I'll start with a compression test and go from there. I'll try to update if I find anything.

 

You'll have better luck posting on LS1tech.

 

p0300 is a random misfire. how loud is the knocking? i would do a compression check just to rule that out. i know those truck motors have issues with intake gaskets. i just replaced mine on my 5.3 when it was cold it would give the random misfires at idle and lean bank 1 and 2. no knocking though

intake gaskets solved it.

 

Well I think I'v solved it. 175 lbs compression across all cylinders but 0 lbs on #7. No leak down in that cylinder. It's a broken rod. I can't imagine how it happened other than a bad head gasket getting water in the cylinder. The previous owner (my wife's grandpa's girlfriend) didn't know of any issue with it somehow so I'll never know when it happened or what may have lead up to it. There's no such thing as a free lunch!

 

I just wanted to update this thread as a warning to people since what happened to this truck could happen to any vehicle with multi port fuel injection possibly. Especially if it sits for a long time.

As I said, this truck sat for a long time, I don't know its history, I don't know when this happened. But what happened was that the #7 fuel injector stuck open and dumped gas into the cylinder. The cylinder was full of liquid fuel, it hydrolocked, and the rod broke. Collateral damage to this was that the piston got thrown to the top of the cylinder and the valve was beating on the top of the piston so it bent the intake valve. Luckily the rod broke very far down towards the journal so it wasn't swinging around and breaking things inside the motor. I replaced the windage tray, rod, bearing, piston, a bunch of gaskets and the fuel injector and had to have a new valve installed in the head. Since it was such a low mileage motor I replaced that stuff instead of the whole motor, but if it had more miles I would have put a rebuilt motor in it.

I also replaced the #8 fuel injector because it was not firing. So not damage there, but it was the 2 rear fuel injectors that went bad. Because of the rearward tilt of the motor in the truck, or probably any LS powered vehicle, the 2 rear injectors are where gas will sit in the fuel rails. So it seems that after time the fuel in the rails evaporated or drained out or who knows, but those 2 rear injectors may have sat with bad gas above them long enough for both of them to get ruined.

Really, considering the severe damage, it actually ran surprisingly well.