The engine may develop a misfire due to worn valve seats. This fault will cause the Check Engine Light to illuminate. Our technicians tell us the misfire may or may not be felt while driving. They further recommend that both cylinder heads be removed and thoroughly inspected and repaired as necessary.
Engine Misfire Due to Worn Valve Seat on GMC 1500 Pickup
Average mileage: 135,000 (135,000–135,000)
Engine affected: 5.7L V8
5 people reported this problem
1998 GMC 1500 Pickup - 5.7L V8 135,000 mi, Visitor
check engine light won't go out. Po300 and PO306. Engine runs smooth. Did full tune up-cap, rotor, plugs, wires, even replaced 02 sensor and all fuel injectors. Code still on but truck runs fine