Hey, I've been scavenging these forums as well as any others I can find on the web searching for some answers here, and any help will be greatly appreciated, especially if anyone has had and fixed the same symptoms on their truck.

I've got a '98 4.6 HSE (120k miles), and a year ago on a hot summer day with the A/C running, it developed a knocking/ticking noise. One mechanic said valve job, took it to another a month or so later, and he said it's the cam and lifters. He replaced that, charged my over $2k, then said it's knocking when it's hot (like I never said that when I first brought it in). Recently the head gasket blew, and now completely distrusting mechanics, and being mechanically inclined, I pulled the heads, replaced the head gasket (along with the exhaust manifold gasket and others along the way), and sent the heads out for a valve job. The days didn't get too hot, and the truck ran fine for a week, until one hot day when I was doing a lot of in-town driving and idling—same problem.

So once again, it knocks when it's hot.
It's a consistent, even knock.
Noticeable at idle, but not so much over 2,000 RPM as the knocks probably just blend together at higher rpm.
Cam & lifters replaced less than 7,000 miles ago (if that).
Checked pushrods when doing heads, and they're all straight.
Valve job and head gaskets replaced.
Exhaust manifold gaskets replaced.

My current ideas are piston rod(s), bad A/C pump, bad water pump. Heavily leaning toward the rod idea, since I'm skeptical the pumps would make this noise—especially the water pump with all the water there to dampen it, since the knock/tick is a rather crisp noise. Maybe it's just a bad cat, but would this only make the noise when it's hot?

Most of the stuff I've read on the web is related to knocking/ticking all the time, but again, mine is only when it's hot. I could be driving the freeway at 70 mph with the A/C on for 45 min, and it won't knock—but then again, if it were 100 degrees outside maybe it would—but if I'm sitting in traffic on a hot day for 10-20 min it'll knock.

I really hate to make my first post a cry for help, but I'm at a loss here and out of ideas...and would like to see what everyone thinks before I go tearing through my motor.

Thanks for any help, it's greatly appreciated.

 

Send me your tele number and I'll call you and try and help.

 

I have the same problem what was your outcome?

 

I have absolutely no background or experience on this, but if you replaced what you said you did and everything looked fine. My thoughts are bad cats. See if you can pin point the noise. Take a stethoscope and see where exactly it is coming from.

 

You can eliminate the accessories by removing the serpentine belt for a couple of minutes. Be CAREFUL, your water pump will not be circulating coolant at this time.

 

Forgive me if I'm wrong, but won't that disengage the oil pump?