I hear a slight rattle sometimes, coming from the engine area in the 2750-3500RPM range when just cruising in gear, is this detenation??

 

Pretty unlikely.
However, after reading your other post, though, it very well maybe possible that your primary injectors are slitgly plugged. Since they operate from idle to 3800 rpm, and the secondary's then kick in, you may be running lean at idle and in the lower rpm ranges, causing detonation.

Detonation normally occurs at WOT at higher rpms, but semi-plugged primaries could definitely do it. Try running a two bottles of fuel system cleaner in 2 gallons of fuel, until the tank is almost empty. If that doesn;t work (and you've confirmed running lean at low rpms with an a/f meter), try getting your primaries professionally cleaned or replace them.

Also try cleaning the pump fuel pickup screen.
Your primaries would not be completely clogged, otherwise the engine would not run at all.

If you think it is detonating (sounds like a metallic "ping" or popcorn popping, stay out of WOT. Detonation can snap an APEX seal instantly and kill your motor, requiring a $1200+ rebuild.
Sean Cathcart

 

I agree, very unlikely. Detonation under low load cruising, would be indecernable (to the ears). Detonation will also cause a timing retard, given your knock sensor works properly ! It is a noticeable thing, the engine itself will change tone, and you will lose a bit of power (not like fuel cut).

Are you sure it's not your shifter or something else rattling. Those revs are the exact revs where every rotary I've driven/been in (droans). You know what I'm talking about... gets vert LOUD, even under light load (unless lifting).

 

Thanks, I'll give it a shot today,

 

oh yea, one more possibilty, a couple people have suggested the o2 sensor? I dont consider this too likely cause why would it just start acting up after the tune up??