Son bought a truck. It is very clean and its his first vehichle. However, it backfires. he changed plugs,wires,cap, rotor. disconnected exhaust temp to check if it was cat. Nothing. It still backfires. He took top plenum off to see if it was injectors no gas leaking but alot of oil film. It is thicker on side with 2,4,6, cylinders. There was small pool of oil also. Could the oil run down the maifold into the head cause the valves to stick. Checked compression cold didn't heat up motor and now its apart. but compression cold was about 210. I really don't know what else it could be. If he needs to take apart and get valves done he will. It is a high mileage engine. 180,000. Any help would be appreciated. Thank you, Lisa.
