I think this engine issue originally started at 78K miles. The engine started idling rough and erratic. At that point my regular mechanic diagnosed and changed the spark plugs and wires. Engine ran great until 95K. Local mechanic suggested returning to dealer because he felt there was a major internal issue. The service bulletins indicated problems with the motor. The dealer had the car about two weeks and replaced the heads and some other internal issues for a price of $2800, but it was covered by GM under warranty. Car ran great but started using 1-2 quarts of oil between oil changes every 3500 miles. At 128K miles the plugs were fouled again and replaced plugs. Had an oil change at 132,000, then had one at 135K and engine started to knock. We thought it was either the water pump or belt. But it was something in the engine. The dealer indicated it would take 12 hours of labor to remove the cylinder heads and diagnose the problem. There is a history of misfire codes in the computer and the diagnostic report indicates an issue in the number 4 cylinder. The other option the dealer indicated was to replace the motor.

So an engine, where we have consistently changed the oil throughout its life, has now failed at 135K. I'm taking steps to replace the engine with a Jasper engine and I will NEVER own another GM product. Since 1997 we have owned 2 Escalades, 1 Denali and 3 Suburbans. None of the others had this high mileage and now I know why I traded them so often. In my opinion, between the flex fuel and the cylinder deactivation, these engines are junk and as the GM fleet ages, the issue will become more prevalent.