LT1 and knock/detonation - lots of stuff tried, still pings
Running 89 octane in my 95 Caprice LT1 wagon. 114k.
Car's PCM has NOT been tuned. No CEL. No stored codes. Barely passed smog in April due to high NOx.
Here's the list of new parts since 4/2015
ICM, coil, MAF, MAP, Coolant temp sensor, water pump (GM), opti (GM), thermostat (180), plugs NGK TR55s, O2s (Bosch), fuel pump, Taylor wires. New EGR valve (GM).
Put in the EGR last week, and my mileage took a dump. Down 3mpg. 10.8 with 100% in-town stop-and-go driving. New EGR is suspect, but the pinging pre-dated EGR replacement.
The car pings when hot, and under moderate load. Audible. Car shows no other problems. Runs great.
Seafoamed the hell out of it yesterday. No change.
Fuel pressure is 39 PSI @ idle and 45-47 WOT at the rail. After 20 minutes key-off, still has 20+ psi. Vacuum is good and stable - no bouncing needle. Tested EGR (per Shbox) pre-solenoid, post solenoid, and at the valve. It all checks out as it should, but the valve is a little slow to respond to vacuum. (Is that normal?) Pushing it in @ idle causes the car to stumble.
Looking at live-data, the ping happens when the EGR opens and under load, and you can hear it.
Disabling the EGR through the tuner eliminates the ping. Car drives fine in this mode, but can't drive it that way forever.
Turned the EGR back on, disconnected the MAF and took it for a drive - CEL on, but no change. Still pings.
Its a tricky one. Any ideas? I bought the Autozone ICM... suspect? Injectors are original - could they be the culprit? Dont think its the opti because the ping stops when the EGR is switched off.
Your assistance would be sincerely appreciated.