I have had a really hard time getting the timing right on my truck so I have been playing with retarding and advancing. My truck has been running way too rich, but from messing with the timing I believe I caused another issue. Lately I have noticed, only on the highway, a top end knocking or pinging sound coming from my engine. It sounded like I had loose rocker arms, but I tightened all of them to specs so I have no idea what the issue is. Could my timing still be off?