I might have found out the problem, I checked cylinder #3 as it temped colder. I stuck my bore scope in there and I thought I seen a chunk of something right under the spark plug hole. So I cranked it till the piston was lower and looked again, it looks like a small chunk off one side. I put a compression tester and got just over 100 cold and it wouldn't hold pressure. Guess I gotta pull the heads and see.

 

If you want to check if your cats are plugged or bad, a good test is to loosen up the manifolds from the Y-pipe quite a bit. If it runs better loosened up your cats are probably plugged. That's what I did to diagnose mine.

 

Sounds like you've found the problem.

 

Well that didn't solve anything. I have the drivers side head off and the #3 cylinder looks normal, I must have been looking at carbon or something. But that doesn't explain the low temp and compression reading. I looked at the intake gasket and that cylinder looks normal. I have one thats questionable with a little wave in it on cylinder #1. Should I pull the other head? I didn't compression test any other than #3. I also bought ARP head bolt kit years ago and never had a chance to put them on. Its a LS6 kit #134-3610. Looking at the bolts there's 2 sizes, large and small. On my truck I have 2 different lengths on the larger bolts, this kit has all the same length for the larger. What do I do about that? I can't reuse the bolts I just pulled out. I also noticed when I drained the oil, the magnet was full of filings.

 

When the head was on, and you had air pressure in the cylinder. Did you take the oil fill cap off and hear air passing thru the base? It could be rings... maybe stick the heads back on and giver that particular cylinder a drop of oil and then crank it. If you are loosing pressure, listen at the oil fill, at the intake and at the exhaust pipe.

Also, pointing a temp sensor at the middle of the cat isn't going to do anything, you need before and after the cat. You want it warmer on the tail pipe side.

 

I never took the oil cap off, I floored it and cranked it over about 4 times. I did that about 3 times and got about 100-115, but it wouldn't hold air it slowly bled off. I was temping the cat to see if one was way hotter, chances were if it was then it's plugged.

 

You need to pull the piston, and it might be a good idea to have a machine shop pressure test your cylinder head too.

 

You can't diagnose a catalytic converter correctly with one temperature reading.

You need two readings, one at the entrance to the cat, and one at the outlet. The catalyst reaction in the cat will create heat, making the outlet temp higher then the inlet.

Also, what were the readings on the rest of the cylinders in that bank?

Did you have all the plugs out during your compression test?

 

For the cat, that's why I did a pressure test before the cat, oft was plugged, I would have had back pressure.

For the cylinders, I got a reading of about 50psi on #2,4 on 6 I got 150 then I gave up and started to pull that head and ended up rounding a few head bolts and rounded a few rocker arm heads and cracked 2 sockets trying to get them li'll buggers off. Need to get I pact sockets as they're thicker(5/16). And see i I can get a 15mm 12 point socket to get the main head bolts off or a special rounded bolt remover.

 

You used a pressure gauge threaded into the first 02 bung correct?

YOU ONLY HAD 50PSI IN 2?!