I have a 07 avalanche with a LMG 5.3L and has a knocking or even a slapping sound under load... Meaning when I punch the has and while going up hill it makes a clunking/knocking sound. I've put full synthetic oils, titanium plugs, K&N surfeited. Bought new knock sensors, cleaned the carb and the MAF... Is it something internal? kinda shame when u try race someone and u hear the clunking sound. Need help.

 

Detonation?

 

What octane gas? How much timing? Does it do it cold and warm?

 

Are you able to log it while it's doing it? Be curious if you are getting knock or not

 

Ever since I bought it I use 92 octane and every other fillup I add a booster and a cleaner in the tank... I even tried stopping the additives, still the same. How much timing? I don't know and how can I adjust it with the ls engine.

 

I meant iridium plugs.

 

NGK Tr55's are what most of us use.

The knocking, is it only at hard acceleration, or do you hear something at idle? B/c when I had the knocking on my '02 5.3 your could hear it hood open and and at idle. Fortunately had the lifters and knock sensors replaced under warranty.

Another question comes to mind is did the previous owner beat the crap out of it to the point where swapping to dual gold springs, 740 chromoly rods, and maybe a valve job maybe in line? And maybe if you're going to beat on it once in a while making the swap may be good preventative maintence.

 

I bet its your carb.

 

Lady3bglover: yes it's under heavy acceleration. I don't know much about the previous owner bcuz the truck came from the states and bought it in Honolulu Hawaii.

 

Last time you changed the "Texas Tea"?