Knocking Out!

[mistermike559]

Had made this post at another forum, with no luck. Hope someone can give me some advice-

 

I know I don't have the morning piston slap or knocking. But recently started with what sounds to be low knocking sound after the truck warms up, an I drive it. Again, while it's warming up in the morning, it doesn't make the noise. Also Doesn't get louder with acceleration. If I come to a complete stop while its doin' the knock sound,I can turn the truck off, an turn it back on- it goes away?? Funny that it goes away when I turn vehicle off, then on? , Once I get going again, an come to another stop, it'll be there? Its' a 2000 4.8l with about 150thousand miles? Any thoughts?

 

I'm going to change the oil even though it has less than 2K miles this weekend, going with something thicker. If this doesn't help, hopefully any advice you guys give me would point me to the right direction. Thanks.

[pennzoil29]

Did you ever consider an exhaust manifold leak? It can sound like a knock or ticking noise, and it can come and go.

[mistermike559]

Thanks, Pennzoil29 for replying back. I finally found out what the tick/knocking sound was. Please if anyone else has the same type of tick/knocking symptoms, check your EVAP Purge Solenoid. Today, I took the truck out to warm it up before I was going to change the oil. When I got back, I left the truck on, an opened the hood. Had the noise going. I took off the plastic cover(VORTEC) to see if I could hear it better. It sounded so close to the TB. I could feel the knock on the intake, an TB. Got close to the Purge solenoid, an bingo. When I disconnected it, the knock went away! I pulled it off, cleaned it up, added abit of hi-temp silicone around the base(hopefully it'll keep the knocking vibration down abit). I hear GM's are known for this. I don't have a CEL code, so I don't think it is bad. But, a few weeks back I had removed the insulation from the underside of the cover because it was falling apart, so that might be the reason why I probably hear it now. I went ahead an also sprayed some undercoating an sound deading spray on the underside of the cover. I let it dry before putting it on.

 

Hope this will help anyone getting a tick/knock an can't figure it out. It's the first an cheapest thing to do to rule on a knocking motor first.