Vehicle is a 2003 Grand Caravan Sport with rear AC, (3.8 motor). I am trying to diagnose a knocking noise that is not steady. It happens when I start the vehicle and gets worse when I turn the AC on. It lessens when the van warms up. I think it is coming form the AC compressor. But if I use my stethoscope, the knocking noise seems to be coming from everything that is connected - the oil pan, the compressor, even the top of the motor. When I took the serpentine belt off, the alternator spins fine, the AC compressor clutch spins fine, the compressor itself seems to be stiff but turns smoothly, the idler and tension pulley spin fine. The vibration damper turns slightly, (I always thought this was a drive wheel attached to the cam shaft?) but it turns slightly, very stiff.


I have seen mentioned something about the damper being bad and causing rattling noises. Is there anything that can go bad with the vibration damper?


Will the AC compressor be working but something inside it be rattling around?


Is there any other suggestions to look for?


Thanks,

 

Further to my last post, I went out and did a little more diagnosing and I removed the serpentine belt and ran the motor for a few minutes and the noise was still there. Ruling out alternator, water pump and AC compressor. Found out that the large pulley on the drive shaft is called a harmonic balancer or vibration dampener. The vibration dampener seems to be rock solid, no play sideways, only that I can slightly turn it in a circular motion, but it doesn't appear to be wobbling at all.


Can anyone tell me what would indicate a bad vibration dampener/harmonic balancer?


Thanks

 

Could it be piston slap? That would explain the noise when it's cold and slap does either go away or lessen as the engine heats up.

 

Any chance of a youtube video showing the noise?

 

Ok here goes the following link is not me but it is the exact same noise The next is me with the balancer removed
The major rattling has gone but there is still a thump and a little rattling left .
Would this be because the engine needs the balancer or is there still a problem in side?