2003 Tahoe Misfires

My 2003 Tahoe has 145,000 miles. I took it to the Chevy dealer when the check engine light came on. They discovered misfires on clyinders 1,6, and 8, and determined that the problem is not being caused by compression, wires, plugs, injectors or coils. They believe the problem is internal although the engine runs quiet. They don’t recommend repairing or replacing the engine because of the 145,000 miles on the car. They did think the problem could be valve related and said I could try an additive. Any suggestions?

Can you detect this misfire when driving the vehicle?? Is the engine jerking and running rough? Does it idle smoothly?

Translation: They hooked it up to a diagnostics machine which could not pinpoint the problem and none of the “mechanics” who worked there could figure it out either.

If it were mine, I would change the fuel filter, check the fuel pressure at the rail, let the gas tank get down to less than 1/4 full and dump in a can of BG 44K fuel system cleaner. I would then change the plugs and wires and during that process, perform a MECHANICAL compression test with a direct reading gauge.

I and they can’t detect anything while the engine is running or idling. According to them, the misfires occur when the revs are increased. I feel nothing while driving down the highway at 75+. The plugs and wires were recently changed, and the same three cylinders misfire even when the plugs are swapped. They said my fuel pump pressure is down but don’t believe that is causing the problem because the same three cylinders misfire. They did not mention the fuel filter as a possibility.

The misfires in those cylinders might be caused from carbon deposits on the back-side of intake valves for those cylinders. These deposits can act like a sponge where when the injector fires, the carbon deposits absorb some of the fuel intended for the cylinder. This leans the mixture out for that cylinder and it misfires. You can try the poor-mans decarbonization of the engine.

Purchase a can of Seafoam Motor Treatment. Get the engine up to operating temperature and shut off the engine. Remove the vacuum hose from the brake booster and adapt a hose that will fit inside the brake booster hose and into the can of Seafoam. Take a pair of pliers and pinch off this hose. Have someone start the engine and bring the RPM’s to 2,000. Slowly open the pliers so the Seafoam begins to be drawn into the engine. Close and open the pliers and keep the RPM’s up to prevent the engine from stalling. Once all the Seafoam has been drawn into the engine, shut the engine off. Reinstall the brake booster vacuum hose. After a half hour has past, restart the engine and bring the RPM’s back up to 2,000 until all the smoke from the exhaust clears. Take the vehicle for a cruise and see if the Check Engine Light comes back on.


Thanks. I need to get up the nerve to try this since it may be pushing my abilities. What is the non poor-man’s decarbonization of the engine?

You take it to shop that has a machine for decarbonizing engines, and pay them $150.00 for this service. A lot more expensive than a $7.00 can of Seafoam.


Thanks, I may do this since it may save me from getting a new car which I don’t want to do.