The '94's knocking sound seems to be getting louder. I would like to inspect the flex plate, since I have covered all the usual suspects already. Any tips to accomplish an inspection of the flex plate?

Just timed the ticks about 6.25 per second at idle around 750 rpm (12.5 revs per second) on the dash. So, one tick per two revolutions. Maybe not flex plate, maybe a cylinder.

 

pull the inspection panel (moon shaped) and use a 'boroscope' of some kind. I bought one on Amazon a few years ago when I suspected my flex plate (turned out to be nothing). Video here...

The trouble is that the flex plate is behind the 'fly wheel' where the reluctor rings are located. The only way to really see it is to sorta look past the bolt heads that secure the flex plate to the torque converter.

Here is what you'll see when you remove the plate... i've circled the bolt head you'll need to look past.

 

Walt, thanks for the photo, very helpful.

Still working on this problem. Tried removing spark from cylinders one by one. I did not notice any change, knocking did not go away. Crawled under with engine idling and a rubber tube up to my ear. Definitely pinpoints sound to rear of engine. Interestingly, clearly hear knocks on right side cat, but not on left side. Only burnt my arm once. Still need to do the visual on the flex plate.

 

Check the reluctor ring attached to the flywheel very carefully. The reluctor ring on mine had come loose at one of the attachment points and was hitting my CPS causing a knocking sound and a hell of a misfire.
That's one of the only times I've paid a shop to do the work for me since the transmission had to be dropped to replace the flywheel. Luckily a local LR indy shop had a used flywheel, flex plate, and torque converter on hand.
I had them replace the flywheel, flex plate, torque converter, and rear main seal while they were in there.

 

I parked the truck ('94 3.9L) because it's space in the garage is taken at the moment. When I get to it, I'll be checking the valve train first, since the tick is in sync with the cam shaft vs crank. Used a stop watch to time 8 ticks (several times), then did some math to compute RPMs. It came out near 1/2 of the tachometer reading.

Some time ago, I installed a new set of rocker arms and lifters, so I'll check for a loose bearing cap on the rocker arms (read about that on this forum) and for a stuck lifter and for a bent push rod. Listening carefully with a tube, it sounds like cyl 8 or 6, maybe? Maybe the right bank? Tick did not really change when spark was removed, so could be valve train noise. Planning to slip a 2 mil feeler gauge on top of the valve stem (engine running) to try to pinpoint which one. I think (hope) it's only one?

Truck is really running great, by the way. Just had it up in the Blue Mountains on logging and NFS roads. In the mean time, I will be running around town on my 49cc Yamaha Zuma (132 MPG, 40 MPH), while the weather is still good.

 

One tick per two revolutions of crank would tell me that it is a cam driven tick. I have one that starts right as the temp gauge reads 175° F. Like clockwork. Lifters and rockers are nasty.