Before and after i did the tune-up to my truck, i've noticed a rattle type noise coming from the engine when im passing someone or just ***** out flooring it, it almost sounds like valve train noise, but im thinking it could be the A/C comp or the tensioner for the A/C? I've know the tensioner to go bad in these trucks and the compressor as well, but it doesn't make this noise when its revved, only when the truck is hauling ***. Any clues?

I run Mobil 1 syn 5-W30
tune-up was NGK IX plugs
Replaced old Volant system with a new one and air tube
Added Trans Dapt TB Spacer with gatorback S-belts.

 

Like marbles in a metal coffee can rattle?

 

yeah you can say that, but i think its intermittent though?

 

that was my first symptom when my cats were going bad...

 

Spark knock-detonation?? I always say it sounds like change in the astray..

 

Fill up with fresh 93 octane first, see if that fixes it. Might be spark knock as Mangled03GMC said

 

Good point guys! thanks for the feedback and i have been running 89 from Shell in my truck and i NEVER do that, always run 93. but with gas prices going up and down like a yo-yo and trying to save alittle money at the pump i thought i was doing myself a favor and ended up having a headache. Just filled up with some 93 and ill see what happens.

 

I would say its the 89 doing it. Go 93 and see if the noise stops. At one point I had a hand held tune like you do (hypertech) which would make my truck ping like crazy if i put anything less than 93 in it. Even at 93 it would ping from time to time. A custom tune can take care of that. I see your saving for a Nelson tune. That will help with some of your issues as well.

 

If you have access to a scan tool that has GM Enhanced software, you can monitor KR (Knock Retard) to see if what you're experiencing is actually audible detonation. I've always used the "marbles in a coffee can" description myself. Roll down the windows and try accelerating up a steep hill once the truck is up to operating temp...if it's detonation, a load such as that should make it happen

 

i get the same thing when i run the 87 here in san diego. with the 91 i cant say that ive ever heard it.