Sierra770

Thanks to Wrencher and all the help on this forum. It was the O2 sensor. Problem is fixed, as is the annoying driveline "POP" upon accelerating from a stop (the typical bone-dry slip joint). I've been putting up with that noise for almost 5 years now and never could figure out what it was until I found this site. Thanks for the help. Eric

Thanks Wrencher. I'm taking the truck to the shop today. I've printed your reply...maybe it will help them. At 115,000 miles, it was due for new plugs and wires anyway, so I'm not out anything YET. I miss the good 'ole days of carbs and a distributor. Technology certainly has given us more horsepower WITH greater fuel efficiency, but gone are the days of fixing it in your own garage. Eric

I've located the fuel rails...one on each side. The feed line comes up from the back of the motor, T's just above the driver's side fuel rail, and runs over the top of the intake, and plums into the passenger side fuel rail. There's no regulator anywhere on top of the engine. There are no vacuum lines running anywhere into the fuel system that's visible from on top. There's a hard plastic line that runs from the top front of the intake, down behind the back of the engine, and connects to a metal line that parallels the fuel line back towards the tank. I'd read that the Flex Fuel vehicles had the regulator in the tank. Mine is not a Flex Fuel, but I wonder... I started it up today to check for leaks around the intake gasket (none). It idled fine for about thirty seconds and then picked up a really rough idle again. That's pretty much the norm. Eric

115,000 miles. No noticable leaks and I have not had to add any coolant. It just started doing this maybe two weeks ago, however, it was intermittent initially. This is the third time, and the longest it's been acting up (over two days now). I've read that the fuel pressure regulator can be an issue, and to check the vacuum line. Where is the FPR on this truck? It's not on the fuel rails and it's not visible in the fuel line that I can see coming up from the rear of the motor. Eric

I started having a rough idle issue with my 2004 Chevrolet Silverado, 5.3L (T), and the check engine light is on. I took it to my local mechanic and he pulled the codes. The scan tool showed an O2 Sensor issue, multiple mis-fires on cylinders 1,3,5,7, and it showed a lean bank. He suggested I change plugs and wires, which I did. I noticed that plugs 2,4,6,8 had almost completely white insulators (lean), whereas plugs 1,3,5,7 were completely covered with black soot. Changing plugs and wires made no difference. It seems to idle fine on initial startup, but after about 20-30 seconds, it becomes rough. It feels like it is running fine once off idle and highway speeds, but it feels like it's about to die when idling at a stop light. Any ideas? Eric