I have a 2000 Tahoe NBS and it has 112K on the clock. Recently when I first start it, it makes a tapping noise which goes away within 10 seconds. I doubt that its bottom end noise because I heard that one before on my old car and it didn't go away. I'm thinking that it's a lifter gone bad but I could be wrong. I have put new plugs and wires in it thinking that it would fix the problem (also getting the flashing SES light sometimes) but it did no such thing. I need help!!! I forgot to add that the codes that I pulled were the O2 sensor, and random misfire cylinder #2.

 

It could be a lifter, or it could be the infamous piston slap that is characteristic of the GM GENIII engines. The piston slap is very common and GM states that no repair attempts should be made as it won't harm anything. The codes are a different story, you need to diagnose the misfire and see if it has anything to do with the O2 sensor code, or if you have a failing O2 sensor...

 

Thanks for the input, I was kinda leaning towards the O2 sensor but I never imagined that it would cause a misfire the way it has been.

 

I see Billy beat me to it. :nunchuk1:

 

If you have a cold air intake they can throw codes. If that is the case, then adjusting the MAF table will fix it. I also have the lifter tapping that makes the engine sound like a sewing machine. I'm using better quality synthetic oil to fix it. Try RISLONE oil treatment in a yellow quart bottle at an auto parts store and see if it helps.

 

lucas works good on mine, u can also try a little thicker oil, i been thinking about trying that z-max oil treatment, i herd it works good.