Kurt D

iTrader: (2)

I'm getting 3-4° of retard at WOT. It's usually in the upper RPM range when it strikes 5-6K. i.e. If I roll into the gas it has 0° retard until 5K rpm. I've replaced the knock sensors (had a bad one), its still there. I've cleaned the MAF and IAT, still there. I've richened the A/F mixture 1% with the Preditor, still have KR just not quite as bad, 2-3° (it's blowing a little black smoke, which should mean it's rich already, right?). I'm running 93 octane, even tried a couple of different brands; Exxon, Texaco, Shell, etc. I know it's hot, but the KR is there whether its 70° or 90°+. In the winter it was around 1°. KR is only at WOT.

What else is there to try? Spark plugs? Did them last year. Coolant temp is pretty steady at 180°. I'm about to remove the Preditor tune and try bone stock this weekend. Any other ideas?

JWRENCH

You might run some GM topend cleaner through it. I've heard several people say it helped.

CAT3

iTrader: (9)

YOu dont have any exhaust banging do you? I had my true duals hitting the DSloop and it pulled major timing due to massive knock!

jimmyblue

iTrader: (11)

Black smoke is probably from lean misfire.
Lean makes hydrocarbons, rich makes CO (in
the region about stoich). You have more PE
range (-5% - +5%), why not try it out? Let
your O2s tell you where your mixture is at,
get it to 900-920mV and then mess your timing
around to whatever 900mV will take.

Bad top end fade might follow fuel pressure drop.
Wiring, filter and aged pump; injector crudding?
A logger like ATAP that tells you about individual
cylinder misfires might put you on the track there.