I have an '86 jeep comanche with over 380000 mls that has started to tick on acceleration and through gears. Also at idle. Have changed motor mounts, transmission mounts, track bar, rear differential fluid, brake pads and rear driver axle and bearings. It always smells like exhaust! Pyew. HELP? And it is a manual. Oil level is ok. But need to tighten the valve cover.
Alright! An 86 Comanche, XJ/MJ's are my specialty!
So you said it smells like exhaust, the sound at idle sounds like a 'pft, pft' sound and the sound while driving sounds like a ticking sound.
It sounds very much like an exhaust leak.
Tracking down the leak:
First I would check the manifold to block connection. These loosen up over time on these inline motors due to their reverse-flow design. Tightening these bolts back to spec will normally fix this issue unless the manifold is warped which is possible if it was not torqued to spec properly or has come lose for an extended period. With over 300,000 miles, you're definitely due to to check all the bolts on the Jeep to make sure they're torqued properly.
You can easily check if it's the manifold to head connection by looking for sooty deposits around the manifold, or by holding a piece of tissue paper near the motor at the flange with it running. If it wiggles, you found your leak! (disclaimer: when the engine is cool of course). The mechanical fan is on the other side of the motor and shouldn't cause any breeze, but make sure you turn off the A/C or the electric fan will skew your results. If torquing it down properly doesn't fix it, replace the gasket.
Next I would check the actual manifold. Because AMC/Jeep designed these motors to run particularly inherently lean, they run SUPER HOT which means that the metal in the headers tend to fatigue, weaken, and eventually fail and crack. You will usually be able to see failures at the collector, and rarely further up into the mounting flange on the motor.
Finally I would check all the other exhaust connections under the vehicle to make sure they're not damaged or leaking. If it sounds like it's coming from the engine bay, it's likely the manifold or manifold to downpipe. Otherwise, it could be where the cat bolts to the downpipe.
A clogged cat can also cause excess backpressure which will result in leaks and the aforementioned "Pft" noise.
It certainly sounds like an exhaust leak. Check your connections, check the pipes for any rust, the collectors are notorious for rotting out because of how inherently hot the Inline motors have been designed to run for emissions.
The best way to find a noise is a stethoscope.
For the ticking, I would listen in the valve covers to see if it is lifters. Since you mentioned a pft sound and exhaust smell also, you should check your exhaust manifold gaskets. If you do not find anything there, work your way down the exhaust system and look for leaks. Be sure to check all around junctions