I have the 92 trooper with 3.2L SOHC, and the ever ticking valve noise.
I tried every additive, treatment etc. with no luck. It would come and go.
Last resort was a procedure in the ISUZU TSB, changing to Mobil 1 0W-30 Synthetic. No luck, lifter still ticking (this is a very loud noise and
makes driving a very unpleasant experience.) I am now in the process of
the hydraulic lifter cleaning procedure detailed in the ISUZU factory TSB
on this subject. This procedure is no quick and easy project. Set aside
at least a few days, more like a week, especially for the home mechanic.
There is a LOT of stuff to take off the engine BEFORE you can even get to
the valve covers. YES you will have to pull both cams, and all rocker shafts, then carefully disassemble each rocker and each lifter individually
cleaning all oil passages very carefully. Especially the rocker and the
shaft. These have very small oil passages, only slightly larger than a paper clip in diameter. Mine had numerous clogs in the rocker arms and rocker shaft oil passages, even though only ONE lifter was noisy. ISUZU
says the hydraulic lifters are NOT available separately and must be purchased along with a new rocker arm. The tiny "O" rings on the lifters
also are NOT available separately from ISUZU, so be verrrry careful with
these. While all this is disassembled, there are many short rubber hoses
that cannot otherwise be reached. Replace all. Also you will need a new
timing belt, and the tensioner and idler pulley, and a new water pump too.
New radiator hoses won't hurt either. Get LOTS of spray carb cleaner and
a gallon pail of carb cleaner for soaking the lifters. Steam clean the
entire engine BEFORE starting anything. I have about $500. in parts. I can
now plainly see that no additive of any kind would have ever cleaned these
oil passages and lifters.