blackvette1

I have a rattle noise which started recently which I only hear on the highway around 70-75 mph and only when I am in 5th gear at part throttle. I had never heard this before and I don't hear this noise any other time. It seems if something was loose and rattling I would hear it at other speeds and in other gears.

Is this rattle type noise detonation? I'm not really sure what detonation sounds like but I've heard it referred to as marbles in a tin can which is what this sounds like.

loudsam

You remember when I was talking about "spark ping" at relatively low rpm at about 3/4 throttle? Everyone seemed to think that spark ping, (detonation) only happens at WOT and high rpm's. I asked the guy who does the dyno tuning at Lingenfelter's. Basically, he told me it could happen at any rpm, and could very well be spark ping from what I explained, especially due to the fact I'd just added headers.

Anyway, I think it's "possible" your experiencing "spark ping" But, you would think that it wouldn't occur unless some variable was changed, ie; new mods or something!

blackvette1

I thought I had heard before that it could occur at RPMs other than WOT. I had my car dynoed recently and there was not detonation at WOT.

My NGK copper plugs have over 20K miles on them so I am going to check them they probably need to be replaced. I will probably also do a decarb since I have 63K miles and haven't done it before.

loudsam

I hadn't thought about carbon build-up. I drive my car too easy alot of the times! Maybe I was just able to hear it more after I installed the headers! Let me know what you find out, if you would please!!!

plaster

I had a guy with me this weekend downloading engine load for a re-tune. Mine does it at very low rpm, under slight loads (15-1700 rpm, accelerating in 6th). Thought it was just a heat shield or cat component that has came loose. Nope. Guy said thats detonation. Unfortunately, I do not know what plugs I have or when they were last changed (recently purchased car). Keep us informed if you find anything.

blktie8

Get it tuned and a de carb is always good after 40 k miles and a dealer can do the de-carb ,if you trust them .
Headers usually make the car richer,A good LS1 EDIT TUNER can take care of this
It needs a tune, if you are sure it is detonation.
1500 in 6th is to slow anything will detonate .
Down shift!