Hello, I have a 1995 K1500 Suburban with 5.7l engine with throttle body injection with 181,000 miles. It runs great except for the following condition: I drive to and from work each day about 25 miles one way. I reach highway speeds and I believe the engine gets thoroughly heat soaked. After about 15 miles, the "Service engine soon" light comes on every day. I believe the computer is OBD1, it has the 12 pin connector. I followed a procedure I found that says to ground pins A and B in the connector and turn the key on to retrieve codes. It did not flash, meaning to me the computer hasn't saved any codes, or this grounding in the connector doesn't work or some other problem with communication with the computer. Would anyone have suggestions? One side note about the engine. While the engine is still warming up and has not reached operating temp, the engine has a significant pre ignition knock when you put the engine under load. It reduces as the engine reaches operating temp. Any suggestions from anyone would be appreciated. Great website!