rephrasing old question

[bwolsen]

I posted before that the nosie made by my 98 k1500 5.7L was a clicking. After listening more I have found that this seems to be more the problem:

 

When the engine is cold, I can turn it over and it will start just fine. However, as soon as it starts, I hear what sounds to be a severe exhaust leak. When I try to rev up the engine, the car shakes just a little as if it is missing.

 

The sound subsides once the engine reaches at least 120 degrees, so does the "missing". Once warm the truck runs just fine.

 

I have trouble finding out where the noise is coming from. I've used a stethascope and found the slight clicking but I don't think that is it. Off advice from others, I changed the manifold and flange gaskets. (the manifold is not cracked) I also changed the plugs. I still get the same problem.

 

Its tough to diagnose because it takes so long for the engine to cool back down. Any help is appreciated.

[GMC_MTR_4X4]

Are you sure its not the valves ticking cause it seems to be a problem with alot of chev/gmc trucks in cold temp. I have a 97 z71 5.7 and unless you run heavy oil in it the valves howl until it heats up almost sounds like a diesel. and one thing I did to get it to shut up was just add a STP fuel additive or an engine treatment. all those do is gum up the valves or sprigs or what evers loose to keep it from rattling around quite so much. does your vehicle have high miles?

[bwolsen]

I'm pretty sure it isn't them. Like I said, it sounds like a severe exhaust leak at first. Then it dies to more of a clicking and after about aminute, its gone. When revving the engine, the truck shakes a little like its missing. But that stops too after its warm.

 

By the way, the truck does have 120K miles on it. A friend mentioned that it could be the catalytic converter. Does this sound right?

[GMC_MTR_4X4]

Well on that truck you should have two cats and they are welded to the rest of the pipe. They could be clogged up.I doubt there leaking but you could pretty much tell just by getting under there while its running just throw some water on the welds and look for bubbles. I think that if it goes away after heating up it could very well be the valves but you would have a better idea then I would. Its just that gm's are notorious for that.