A flashing SES light indicates a rich misfire on more than one cylinder. It flashes to warn you that damage to the catalytic converter is likely to occur. A vacuum leak will cause a lean misfire. A scan tool would be necessary to determine what's going on.


P0300 at high rpm under a load could be any one or more of several things. After exhausting all other options, (plugs, wires, cap, rotor, CMP retard, crank sensor relearn, fuel pressure & volume, etc etc) there is another possibility that is a little more obscure, and more difficult to diagnose. Valve stems can bind in the valve guides. GM has a TSB addressing this issue, and your 2001 is a candidate.


Something to keep in mind... cylinder misfire is detected, and the offending cylinder(s) are accurately identified, using both crankshaft and camshaft position sensor data, (combined effort). If the crankshaft position sensor relearn data is incorrect, and or camshaft retard is incorrect, cylinder misfire detection and identification will be incorrect. Point being, need to make sure the tech actually did the relearn, and CMP retard is correct.

 

ok thank you I will start there... thanks so much.