My ‘88 2.9 has the lifter tick and at times it doesn’t. What would be the reason it only does it some of the time and what is the best cure?

 

The 2.9l used the center cam bearings to send oil to the valve train parts, and when the engine gets a few miles on it, the cam bearing, like ALL bearings, gets a bigger gap, so oil pressure to the valve train goes down

You can try adding some Marvel Mystery oil

The problem is the high miles

Before the next oil change is due add a 1/2 to full Quart of ATF to engine oil, ATF is a high detergent oil and can help clean out lifters, run for a few hundred miles then change the oil like normal
You should also run a 10-40w or 20-40w oil in a high mile engine, not 30w