[old_master]

Is the check engine light illuminated?

There is one sensor in each cylinder head. There is one wire going to each sensor. When the knock sensors detect spark knock, the ECM retards ignition timing up to a maximum of 20 degrees, or until the knock is no longer detected, whichever is less. When timing is retarded, engine power output is reduced. If there's a problem with the sensor(s), the check engine light will come on and set a code in memory.

Disconnect the Electronic Spark Timing, (EST) connector, tan with black stripe wire behind the carpet, next to the firewall by the passengers feet. Adjust ignition timing according to the decal under the hood. Reconnect the EST and see if it still has spark knock. If so, check the EGR valve operation and the passages for restriction.