Three problems related to gasoline engine have been reported for the 1999 GMC Sierra. The most recently reported issues are listed below.
The rear rotors u-joint, carbon build up on throttle, replaced window motor uses 2 qts of oil every 400 to 500 miles , transmission uses 1 qt of oil every 20000 miles , air conditioner fan does not work on high I believe the throttle build up is a safety issue with the gas petal sticking. We have a lemon.
Engine knocks loudly at start-up and last for aprox. 2 minutes - dealer said this is a normal occurrence. The engine also has spark knock when accelerating and dealer also says this is normal - dealer said this is due to carbon build up on ring lands and could be temporarily repaired but would re-occur within 10,ooo miles. This problem started at 15,000 miles and continues to date. I cannot solve the problem with any type of additive advised by the dealer. Dealer said GMC has a defective engine and I have to live with it. They told me even if they replaced the motor I would have the same problem with the knocking and pinging on accelleration. The dealer contacted GMC technical advisor dan pratner case # 3970330 and he advised them this was normal for this engine. I find it hard to believe a person can purchase a vehicle with a defective engine and be told this is normal. The public needs to know before they buy this particular product so they do not end up with a defective product that will cause them additional maintenance costs and a very low resale value not to speak of the embarrassment of having a vehicle that knocks loudly on cold start-up. I do not know what the long term effects of this engine knocking will do. If you do investigate this problem and find this to be caused by another problem that can be repaired, please let me know. Thank you for your time.
While driving at 80mph the vehicle will sporadically go out while switching lanes, then kicks back in after a few seconds. Dealer can't solve problem.