A/C causing PK

[r1991_4g63t]

ok heres an off the wall question im asking instead of trying first because im not around my car at the moment.

first off im seeing 43 counts of knock when taking off in 1st driving normal and sometimes 2nd. if i get on it i see under 8 if any. have tried many things to determine its not real knock.

my car still has the A/c compresor but the pulley is fried and not hooked up any longer. one day while changing all the belts, short time before i started to notice the car was running bad, i pulled all the rubber strands out of the pulley. now the pulley moves maybe 3/4in from side to side. is it possible since its mounted so close to the KS that the vibrations from the car taking off, especially after installing the prothanes, are bouncing the pulley back and forth and the sensor is picking it up?

 

[Defiant]

Not likely. The knock sensor is a microphone tuned to pick up the frequencies of a ringing iron block. I'd expect the compressor is too high-pitched for the KS to "hear".

We used to have a great time in the eighties when GM started with knock sensors. Tapping on the tailpipe with a wrench while another guy was working the Sun machine would wreak havoc. Right up until there was a beating.

 

[delta448]

If your pulley is bad and you don't have the belt on it, why are you keeping the whole compressor on the car? You're obviously not using it, so why not have a shop collect the refrigerant and then you can pull the whole compressor off the block to be sure. The mounting bracket is pretty heavy too, but it's only -IIRC- 4 more bolts. I doubt the compressor or it's pulley resonate at the same frequency as the block when the compressor is not even running.

You might be able to use a mechanic's stethoscope with a partner at the throttle to probe around the bay for your PK source, unless it's coming from the driveline or suspension.

Tapping on the tailpipe with a wrench while another guy was working the Sun machine would wreak havoc. Right up until there was a beating.

 

[r1991_4g63t]

it wasnt the compressor itself knocking, it was the pulley hitting the compressor. it had to have made noise for quite some time for whoever had it before it ate the belt judging by how loose the pulley is to the compressor. i secured it and i have no more knock. it will come off completely soon.