99 2500

It might be the #6 ignition coil starting to fail. This happened to my brother's 2000 silverado with 6.0l, it would intermittently miss and sometimes work fine for a couple days but down on power. Finally the coil just completely failed so was easy to diagnose then.

TJ

iTrader: (10)

so last week the motor started to rattle. rattle as in about to come apart. noise was 99% sure on the driver side, and the dealer only had one gasket and head bolts in stock, so i replaced the drivers side lifters.
head was clean. way clean for a 150K motor. exhaust valves werent even chaulked up with soot, neither was the chamber. very clean, dark grey exhaust valves. no build up on the pistons either. you could see a light black on them, with a swirl on the piston. id say the motor is burning clean and healthy. #7 piston looked the worse, but still great for them milage. i was guessing the bad lifter was in this cylinder. checked them all with a screwdriver, but none were busted. put back together. truck runs great, still down on power. now everyday, it rattles again, and then quits!!! WTF!!! does it for about 5 minutes. sounds like its dry of oil and its about to come apart, then the noise gets lower and lower and goes away.

any ideas? im going to pull the pass side head and replace the lifters just cause. if it were a rod bearing, it would have already gone south.
broke ring would be smoking or using oil by now.
crack in skirt or a wrist pin not staying put, but the cylinders on the driver side were good. i know noises can travel, but im really lost now.

put a mark on every weld and hole on the flexplate as i spun the motor over to inspect. it looks like it just came out of a GM box off the shelf. no oil, dirt, clean as a whistle. all bolts are installed (not that i can tell if they are loose or not)

Tootall

iTrader: (79)

Rattles only on startup only? Or just at random times while running?

TJ

iTrader: (10)

slight rattle on start up, then random times while running.
very strange. its has to be a lifter or a rod bearing. it sounds more like a rod bearing, but i dont know how a spun bearing can work its way back in and stop knocking.

as a note, the oil pressure does not change or fluctuate on the gauge at all while its making noises.

Tinbender59

I am not completely sure about this, just a theory but it sounds like you may have an O2 sensor out of tollerence telling the system to cut back on fuel, (thinks it is to rich) you get preiginition knock from to lean and then the timing is pulled way back to compensate for the knock. This combination of lean, and retarded timing would cause your exaust temps to go insanely high. And cause a no power situation. To much O2 in the exaust will cause the cats to get over active as well (I think). Someone also mentioned that the 6.0's are detuned, that is correct!! All of the LS series engines are restricted by a torque control parameter in the ECU. The purpose of this is to facilitate the use of a 4L60E insted of the more expensive 4L80E. If the LS series motors were to have all of thier ponies turned loose, a 4L60E would not last 3 months, maybe some of the programs are a little to active??? who knows??? You will need to get a program that will let you data log the goings on inside of the ECU, to determin what is really going on.

this is a relative cheap system (I have this one)" http://www.obdcom.com/ " works great for data loging and clearing engine codes. once you have some data someone should be willing to help you decipher it. good luck

MikeGyver

iTrader: (5)

Mine was doing that, at idle it went tap, tap, tap, pause,............... tap, tap, tap, pause,............etc. Like the monkey inside the motor tapped on the block with a small ball peen hammer, waited for an answer, and did it again over and over. It was either the cam lobe ruined the lifter roller, or the lifter roller wiped out the cam lobe. After enough of the grindings from the cam lobe circulated through the motor, it took out two main bearings and my oil pressure dropped. I ran it for quite awhile between first hearing the noise and ruining the motor.

TJ

iTrader: (10)

well thats good to know. haha.
mine does it at all rpms. pulling the pass side head monday or tuesday and replacing the lifters on that bank and hopefully she will have a long life ahead of her.
hopefully the power comes back too and i just misdiagnosed the drivers side noise.

TJ

iTrader: (10)

after pulling heads, replacing lifters, cutting open my stock muffler, numerous computers, gauges and testers hooked up and couldnt find the issue, it was the water pump!
it started pouring out of what i thought was the weep hole.

got it off the truck and filled it with water and it was flooding out of the front seal.
my buddy at gm said he hadnt seen one do that. it was always the weep hole or a bad water pump to block gasket.

pump was harder to spin by hand than the replacement. i didnt take it apart, but im guessing a bearing failure. talked with another buddy of mine and he said his tahoe did the same thing. it magically had more power after a water pump replacement.

all is well for now.

i also replaced the stock muffler with the "big oval" from flo pro. they advertise stock sound and its almost that.

truck sounds like the converter is unlocked when it is locked, but thats about all the noise it makes. just a lil hum. its got to be the least noisey aftermarket muffler ive ever put on anything.

stock muffler temps were 360-380 empty and 470-520 while towing.

this muffler is only 150-160 degrees across the muffler.

thanks to all that gave opinions and advice. hope this thread will help the next guy!

MikeGyver

iTrader: (5)

This thread is about your lack of power. Replacing the water pump gave your missing power back?

TJ

iTrader: (10)

crazy. i know. not sure if there was a bearing going out or what. just that lil bit of strain on the motor was killing some HP.