I have a 5.3 litre. on cold start up it has a random teeth jaring tap. sounds like valve slapping seat. #7 cylinder developed a miss. dropped compression to 20 lbs. intake rocker arm did not move when spun over. so I pulled head replaced lifters and push rods. seen no sighns of any mater or scars from anything. it ran fine except the tapping at cold start up still there. 45 miles later # 7 lifters goes out again. oil pressure 65lbs at 1800 rpm. #3 intake #7 intake and exhaust lifters is not oilling. DOD only affects #7 lifters not #3. has anybody ran across this?

 

i would post this on on ls1tech in the ls4 section. ive heard of ppl having issues with the #7 cylinder, but only when running n2o. lifter noise in cold weather is common on lsx motors.

 

I also have a '06 SS with lifters tapping at cold start. While talking to a friend of mine about it he told me of a service bulletin he'd read about a mesh filter located in the lifter oil gallery underneath the old pressure sending unit. This mesh filter clogs and reduces oil pressure being fed to the lifters. Part cost about $7.00 at Chevrolet dealership. Below is a pick of the one pulled from my SS before being replaced.