jason78

I have a 2005 Silverado with 5.3 (non flex fuel) engine. Owned since new. Now have 238K miles. Recently I have started hearing what sounds like maybe knocking in the engine. Or possible "valve slap", I have read about, not sure. This only occurs when the truck is crusing at highway speed. Basically after OD kicks in I start hearing the knocking when running about 60mph+ at about 1600RPM. Still have smooth normal acceleration and purrs like a kitten at idle. When you give it 100% throttle to pass it spark knocks like crazy but has done that for quite a while. Always thought that was the 10% ethanol gas forced on us now.

My check engine light has not come on. The plugs have about 100K on them and the plug wires have never been changed so probably time to do both. I have never replaced any of the O2 sensors or Knock Sensors. Could any of these sensors be causing my problems AND NOT setting off the Check Engine light?

Just trying to find a good starting point and would rather not start throwing parts at the problem unnecessarily.

Any advice greatly appreciated!

Thanks
Jason