Need advanced help with detonation

[John_D.]

The stock thermostat is a 195.

I'd suspect the engine is going a bit lean under load, which then leads to the detonation and subsequent knock retard. 4000 rpms while accelerating has a significant fueling need beyond what you would see measuring the fuel psi at idle. Possibly a failing pump or restricted filter...

Can you monitor a/f, or o2 voltages, while accelerating at wot under load (up a hill would be best), and determine if the o2's are going below .85 volts, anywhere in the range of 3000-6000 rpms?

Highter temps will definitely make the underlying problem worse.

[John_D.]

If it was run with bad plug wires for a while, there may be some built-up deposits in those cylinders too... Might be as simple as that.

[HBHRacing]

I watched 02 output as well as fuel trim. I had no indecaion of it heading lean. fuel pressure was dead on but like you said a restriction can cause a low volume that is needed for high load. I can check again but I am sure that it wasn't going lean. I belive that I had him change the fuel filter anyway but I will see.

With everything that I have ruled out the 2 things that I am leaning (and hoping) for would be an exhaust restriction from the cat or a carbon biuldup condistion. Both of thouse are easy problems to remedy. If we get through these final checkes with nothing then there is not much left other then internal motor issues.

and since the dealer is a PITA with warrenty work it;s not like they would just "try" replacing all the pushrods and rockers.