*sigh* shes broke again

Just in the last few weeks after cleaning the car out from a really bad full tank of gas (more water than anything) I now have a new problem.
My mechanic cleaned the tank, flushed lines, engine everything and ran an entire tank full of 93 octane through it. Now though very rarely, like maybe 2-3 times a week under normal cruizing conditions the car starts pinging and knocking and sounding absolutely terrible. Power almost dissappears as well. It happens for bursts from anywhere between 10-30 seconds when it acts up. The best guess Ive heard so far is tha the ecm is advancing the timing to full for some reason. Why would it do that?

All sensors work and have been tested, there is a new prom in there now, and its a new 350 TBI engine. I dont have the car right now, got it towed back to mechanics. But while he waits for a new ECM is there anything I can let him know to check or look at that might cause this wierd behavior?

 

did you switch to the 350 knock sensor and ESC module, and have you checked the timing? And what PROM are you using

 

I cant find out the answer to those questions till Monday when hes back from racing again, I dont know much at all about this stuff. I do know its a Hypertech prom thats in there and that all the sensors are new so Id assume he used a 350 knock sensor. The ESC Im not sure about but he did say he had one of those on order.

 

Ok, ESC is the origional one, timing is somewhere in the 5-8 degrees range, and the knock sensor is a 350 one. The prom is whatever hypertech recommends for a 350.

Under normal cruizing the car will start to ping and knock really bad, but as soon as you let off the gas and go back on again its fine. Scanner tool brings up nothing, no error codes, all sensors are working right. Hes gonna go throw the old Prom back in to see if it happens to be a bad prom or not.

Failing that any other ideas??