I have a 2wd 1997 GMC Sonoma with the 4.3L V6 and a four-speed automatic transmission. It has 42,000 miles on it. Around 20,000 miles it started pinging/knocking while accelerating.
I took it to the dealership where they replaced the EGR valve and told me to use 89 octane gas. The noise is less noticeable with 89 octane and even less with 93 octane. But the correct octane rating is 87 and it does still make noise even with 93 octane. I've also tried different brands of fuel.
Your engine should not be experiencing significant preignition or detonation when using a quality fuel of the specified octane rating. An occasional light pinging sound under acceleration can be considered normal, but not if it's really loud or consistent. Get your Sonoma back to the dealership and let them know the engine is pinging regardless of the fuel used. They already have a head start on the job knowing that the EGR (Exhaust Gas Recirculation) valve wasn't the answer.
The first step is to install a diagnostic scan tool and go over all the PCM (Power Control Module) information. For instance: trouble codes, too lean an air/fuel ratio, coolant and intake air temperature, TPS (Throttle Position Sensor) readings, EGR operation, and the Knock Sensor.
The Knock Sensor's purpose is to actually hear the engine knocking and then retard the ignition timing to eliminate the potentially damaging condition.
The EGR system bleeds exhaust gas into the air/fuel mixture entering the engine to reduce combustion temperature. This is a necessity in avoiding preignition. There may be a failure in the system other than the EGR valve itself, possibly an electronic command problem or even a blocked exhaust port disabling the system.
Once all the external possibilities have been eliminated, and the latest Powertrain Control Module calibration has been applied, excessive carbon build up inside the combustion chamber should be looked into.