Detonation problem need help

[dirt5track]

I have a 4.7 in my 90 wrangler running '95 wire harness and injection (obd1). Build specs are 60 over block,kb944 pistons, stock rods, stock head, comp cam, hesco adj fpr, bigger injectors, stock ignition.
I don't remember the cam model or injectors. The cam is mild as I am in California and need to pass emissions.
I originally had this motor in my xj till a tree jumped out and totaled it. At about 5k miles I broke #5 piston and at that time it was assumed to be a vacuum leak. I changed the intake and verified I had no leaks after reinstalling everything. Since then I have installed the stroker into my yj and have broken #5 piston again.
The piston is broken at the top compression ring and appears to be a pre-ignition problem. I have installed a new piston and have everything back together and now have a bad rattle that sounds like detonation. Using a stethoscope the sound is strongest at #5 listening at the cylinder head.
Base timing is at 12 deg and total timing is at 34 deg, my wide band o2 is reading 12.4-13.8 afr and engine temp is at 210.
if anyone has any advice on what to check please let me know I am at the point of pulling the motor in favor of a v8.
Thank you in advance, any thoughts are welcomed

1990 yj 108" wb 4.7 aw4 231/d300 dana 60 kp 14 bolt on 40's

[dirt5track]

I forgot to mention that the pinging noise comes on about 1800 rpm and goes away at 2600 rpms. It's quiet at idle and higher rpms. With a stethoscope I can hear the noise at idle but not without it.

[dirt5track]

Update: I changed to ngk 7373 spark plugs and it helped a little bit. The range of rmps that I get the ping is smaller. Also I have isolated that it is coming from cylinder 5 only, when I pulled #5 wire the sound goes away completely.
Has anyone ran into the obd1 pcm advancing the timing on 1 cylinder only? Or is there any other ideas that could cause this?

[SkylinesSuck]

It's not possible for it to advance the timing on one cylinder only. You have something else going on like a good spot in that cylinder or maybe a lean condition? I'd swap injectors just to try something, but you might have to peak inside. Got a boroscope? Cheap ones can be had that work with Android phones.

[SilverXJ]

Using a stethoscope the sound is strongest at #5 listening at the cylinder head.

How are you doing this?

[dirt5track]

Using a stethoscope the sound is strongest at #5 listening at the cylinder head.

How are you doing this?

I have a stethoscope with a metal rod in the tube. I just touch the rod in the area I want to listen too, then move it around to other areas.
I have determined that I have an internal mechanical problem causing my noise. It may be skirt slap so I have decided to pull the motor and go through with my v8 swap. I appreciate the help guys. If anyone is in central Ca. I will have a 4.7 for sale that will need one cylinder sleeved or a new block.

[SilverXJ]

Denotation won't happen at idle or under no load.