Helping out a friend with his 88' k3500 gmc. it has a 454 tbi . it is spark knocking excessively, and timing will go to 41 degrees when the motor is revved(granted no load). There is no knock sensor or esc module on this truck.If it is they hid it but good(not on the right hand block side). Would GMC have put this together without a knock sensor? what would control timing? It has been on a scan tool ,both the map and o2 sensor needed replaced. after replacement there was no change in the spark knock condition. Need help from the guru's ! thanks in advance.

 

You probably have 1228747 ECM with HD emissions. HD application (454) have been known to omit ESC and KS. From your description it appears that base timing is incorrect. Almost all truck application call for 0 deg base timing with EST connector disconnected. After setting base timing turn off engine - disconnect battery for 30 seconds to clear EST code. HD timing is very conservative - this way KS is not required.
For more information check with boys on http://67-72chevytrucks.com/ or FSC
http://www.fullsizechevy.com/

//RF

 

RFmaster, Thanks for the info. He went back over everything and did find the base timing was off.