2004 Monte Carlo SS 3800 supercharged.
Loud knock at idle. Problem originated when idling in a drive thru. The knock as intermittent at first. Very noticeable when throttle was bounced off the rev limiter in park. When load was placed on the motor the sound went away. The sound also went away when all belts were removed from the serpentine system. This is no longer the case. Unable to locate the source of the sound with a stethoscope. Knock seems to be getting worse with time. No noticeable loss of power no codes being thrown. Knock seems to disappear at approx. 1700-1800 rpms.

• Added supercharger oil to super charger. Removed approx. 3 oz replaced with the recommended 8oz no change.
• Added ristone and marvel mystery oil. No change
• Replaced spark plugs on all cylinders and ran compression tests. 60 PSI at idle across all cylinders. No change
• Engine seems to be using oil but does not appear to be leaking.
• Coolant was low. Topped off with water. No issues with overheating.
• Removed inspection plate. All flex plate bolts appear to be tight and found no visible cracks in the flex plate. No scrapes indicating any rubbing. No change
• Replaced harmonic balancer. The original had no rubber separating from the pulley. No change
• Ran motor with each individual spark plug wire unhooked from coil pack. All packs sparked and there was no change when removed vs installed across all cylinders. No change.

 

First off, welcome to the forum


Sounds like it could be one of the following

Bearings
Rod
Lifter's

My money would be on the bearings or rods if it goes away when under load

here are a couple links to help with your diagnosing and troubleshooting process

http://www.foxvalleymarc.com/Tech_se...ne_noises.html


http://www.justautorepair.com/whats-...ocking-ticking

http://www.mhnetwork.com/news/what-s-that-engine-noise/

 

A cracked flexplate causes knocking also

 

I would check the lifters before you get into anything serious

 

A cracked flexplate will indeed cause this also. Just had mine crack and it wound up also chewing up the rear main seal plate so bad that it was dumping oil continually.

Bear with me I'm trying to remember what my nephew said and maybe somebody else can chime in....lifters would be "HALF" the time of the crank shaft? Is that right? I can't remember what he said about my knock but he was able to rule it out as lifters with the timing that it knocked....which was either half that of the crankshaft OR in time with the crankshaft. Again....maybe someone else more experienced can chime in on that one?

Good luck with whatever it turns out to be.