Alright, heres the deal. Checked my exhaust temps and they were pretty close to equal on either end. Differing by maybe 5-10 degrees with the measurement infront of the cat being slightly higher.

As for the rattling sound, I spoke too soon. It does seem to come in right at 2500rpm and ONLY happens once the motor has gotten up to about 200 degrees on the gauge. Before that temp when its cooler I get no "rattle" at all. Also it will not rattle if I'm just sitting in neutral revved up to 2500rpm. But, as I said it sounds like it coming from underneath of the cab.....[sm=insomnia.gif]

Finally, the "knock" that I'm getting is only at idle, and the best way to describe it is very similar to the "knock" that a diesel makes when it idles. Just not so LOUD. But again, just like the "rattle" I'm hearing, it seems to be coming from underneath the cab. Not the motor.

I pulled the throttle body off last night and could not see any oil, but have not had the chance to get any kind of mirror to look back towards the rear of the plenum.

 

your cat is becoming plugged... hotter temps on the inlet side of the cat indicate that it's plugging up. swap it out asap. if your cat's are by the head like mine, better swap the cats now or consider not driving it. Reason... too much heat building up by the head will cause damage to the exhaust valve seats and they will eventually fail. this is what happend to mine. plus, the head is prone to cracking between the valves and excessive heat may contribute to it (not 100% sure on this one, that's my theory anyway).

fix the cat, then look into the knock... they may be related since your cat is plugged/broken...

 

Will this not throw out a check engine code? When my father-inlaw's Chevy Tahoe had a cat go bad it gave him a check engine code. I'm not getting any codes currently.[X(]

 

maybe, maybe not... think about it, what's the purpose of the o2's? the up stream one is used to control the AFR and make sure there isnt too much gas being dumped into the engine. the down stream o2 is there to measure how efficient the cat is working and nothing else. so if the down stream cat sees that the cat is not letting too much unburnt fuel thru, it's happy. and if the front o2 is able to measure the o2 levels before the cat, it's happy. so why throw a code? no reason to....

 

good point.

 

Refering to plentum leak,mineknocked while idling.Take off oil fill cap,if knocking goes away
or gets quieter its your plenum.

 

ok i scanned the replies here and found no pinging on start-up.

2001 5.9l pings loud on cold start. also pings on hard accelaration like others....

is this the plenum?

 

Well, I took care of the problem.. mine, as I said before, was doing all of these things. pinging, knocking, hesitating and studdering at about 45mph-60mph... I needed 7 new spark plugs and 3 new wires, they were completely burned up.. also, I did need new intake manifold gaskets... all in all a very expensive job, but worth it, the truck runs like it did in 1997!!!!
ALso, I HIGHLY recommend RESTORE or LUCAS added to your next oil change.. seriously, helps boost compression, smooths out the cylinders.. I swear by it! get the 8cylinder bottle of RESTORE and see the difference (wow, I sound like a commercial huh?) but truly does wonders for your gitty-up