I have to drive to Denver (my sister is having heart surgery) and decided to take my '93 4Runner instead of the '85 since it gets better gas mileage.
Now, the '93 has been making noise which I was pretty positive was piston slap. It had a fairly noisy ticking/knocking noise in #4 cylinder. When the plug wire was pulled or the injector unplugged, the noise went away completely since no force on the piston. Not a very good test really other than to definitely identify what cylinder the noise is in. What had me thinking it was a piston/wrist pin/bushing was the fact that the sound would start immediately upon starting the motor and never really changed as the motor warmed up.
So, today, I figured on doing a quick bit of minor maintenance before driving over. Fluids, tire pressure, air filter, injector cleaner and since I decided it wouldn't matter either way I did what I consider unthinkable and put STP in the oil after the truck had warmed up. Within moments the sound was almost completely eliminated. Not being the positive "butterflies are pretty, fluffy bunnies make me happy, gosh I love rainbows" kind of person I had no faith in what happened so I went for a drive. I ran the truck through the gears getting the RPMs up and down, idled at stoplights, rev'ed at stoplights, drove for a while, stopped in a parking lot and let it sit for a bit then cranked it back on. I focused a lot on having the engine in the 2500 rpm range. Still the noise was almost not to be heard.
My question then, is this a pretty good indicator then that the noise is bearing related and the now thicker oil is taking up the slack with the bearing issue? STP couldn't mask a wristpin problem could it? I wouldn't think it would be strong enough to support a bad bushing.
Any opinions?

 

Only thing I could think is it may have been a sticky valve???

Engine knock from a piston is real real noticable, just my .02

 

Most likely a rod bearing that is bad.....

 

I'd go with the rod bearing also....3.0s seem to have rod problems. I've never heard of any piston problems...other than a recent "hole in a piston". STP has thickeners that would help take up the slack in the bearing...as you probably know. You also might try running 40W or 50W...but no matter what, You're gonna do a rebuild...I'd just hate to see you have to buy a new engine because this one detonated.

 

Whoops, I forgot to say it is a 22re. I'm thinking of just having all the rod bearings and timing chain while it's apart done for now. It only has 114k on it and if I can get another 50-100k out of it for $600-700 I'll do it.
What I would also like to do is find a couple 4.56 diffs. The front diff has to be pulled to get to the bottom end anyway so it would be a good time to switch gears and the rear diff wouldn't be any big hassle to do.