Geez, I think the FL heat just got me.

H2 started this weird knocking sound a week or so ago. Its not rev specific or hot and cold specific. Oil pressure is normal, temps are normal, etc.

A few days ago it threw a code P0420 and knock sensors. Power sucks. I can clear and it runs fine until the heat of the day then they are back. Knock sound comes and goes.

I think I have what has been previous reported as being a cracked exhaust manifold and or something loose in the cats or muffler. Its been too hot for me to crawl under it.

Anyone have any insight? Power is way down and I get an occasional louder exhaust sound.

Obviously I need to replace the knock sensors. Im hoping O2 sensors and I will either gut the cats or go to a full exhaust system. Anyone have anything more than cat back systems out there?

Tim

 

Forget why I was looking the other day - prolly searching for "clunk" and guggle matched it with "knock". Anyway here's a similar thread to the one I found about the knock sensors. Guess they can be a big problem because of the plastic intake design.
P0332 Knock Sensor 2002 Sierra..help ! - Gen III and IV Small Block & Drivetrain - GM-Trucks.com

 

Yeah, reset the code but as soon as the sensor trips the truck has no power. I had to change mine a couple of years ago. Not to bad of a job if you're good at one arm push-ups... Haha. Pm me if you have any questions

 

THIS IS THE THREAD!!!
Thanks MM, knew I'd seen this recently.

 

OK knocking was from one broken and one loose exhaust manifold bolt. I managed to tighten the loose one and the knock is gone. Truck is now also throwing random miss and mass air flow sensor codes.

I will clear them all and drive some more to see what is going on for sure. I think I do have one bad bad cat.

Still looking for exhaust recommendations. If I have to replace manifolds I might as well put some headers on it and eliminate the cats and run full exhaust.

TH

 

I ran OBX LT headers on my silverado SS. they are basically the chinese version of Dynatech headers which will run you way more money. the obx were full stainless steel 1 3/4 with 2.5 collectors and included a stainless midpipe also. ran them for about 5 years and no problems at all great product. the only annoying thing will be drivers side header hump it will hit #7 plug wire. you will have to tie up the plug wire with a zip tie or it will hit the header. i now run Texas speed 1 7/8 LT's on my ls1 camaro. full stainless with midpipes. im pretty sure they make truck headers now also. good customer service and a stellar product for the price. if you want some big brand names look at Kooks or American Racing (ARH) but be prepared for a 1500+ price tag.

also a misfiring cylinder condition or a bad knock sensor will cause a knocking noise if the cylinder is misfiring bad enough. it will create knock retard which will throw off the knock sensor and make the sound you are hearing.