My Friend just got his 91 4runner with the 3vze motor back from the shop after 6 months of "2 more weeks". Allegedly the machine work was done to bore/hone cylinders, deck the block and cylinder head rebuild.

The vehicle sounds horrible, ticking and hammering. Engine seems balanced so not likely a fuel/compression issue. Engine has about 20 minutes on it since he got it driving it home.
He cannot deal with the shop anymore as it would be up to lawyers instead of getting it resolved. Its my opinion they threw together what they got to get it out of their hair.

Steps done
Listen with a length of hose to see if we can identify where noise was from (I could not, noise is from all over but nothing on the top end that I could tell)
Put a mechanical pressure gauge where the electric oil pressure sender was.
Started vehicle has 0 psi.
Ran at 3000-4000 rpm, it briefly jumped as in moved the needle then back to 0 (It would not hold oil pressure at this rpm) Vehicle sounds significantly worse at higher RPM than lower. To me this means a gross internal oil leak inside of the motor.

He called me as I am a 80's jeep guy, and understand older vehicles, and rebuilt a motor before (recently) of similar vintage. This motor has this "oil cooling" system which I understand but have not seen before on stuff I have worked on.
Want to know if there is any of this that can be serviced in the engine bay. Its not leaking externally anywhere. The oil is super clean/looks new. The motor has 20 minutes of runtime on it at this point.
Here are my likely culprits looking for ideas on what is :"likely" to have been screwed up.
1. Oil suction tube not properly attached to oil pump
2. Oil suction tube gasket missing/sucking air
3. Wrong length oil suction tube installed (It has plenty of oil/Full on dip stick)
4. Oil pump is broken/shot/wrong internal tolerances
5. Oil pump relief valve is stuck "open"
6. Gasket between oil pump and oil coolers/main oil gallerie is somehow bad or missing a plug. (I don't really understand this part of the oiling system). Do these motors have oil galleries plugs anywhere inside?
7. Wrong main bearings installed
8. Wrong rod bearings installed
9. Something with the cylinder head cam bearings.

I personally feel this is likely a gross assembly mistake.
Ideas to try
1. Switch it to 20/50 oil temporarily to see if that increases the oil pressure. This would help in diagnostics but motor still needs to be dropped to rectify.
2. Is there anything with the relief valve on the oil cooler assembly that could cause this?
3. Is there any way to see if there is cavitation in the oiling system that would indicate a leak in the intake side. (Like attach a clear tube to the 1/8 npt fitting for the oil pressure sensor and see if it bubbles)

The only fix "in vehicle" might be the oil pump, or a missing oil galleries plug, the rest is pull the motor and try again. Any thoughts on how to diagnose?

 

You'll need to get it to a competent shop that is also very good at paperwork and documenatation. I don't know what state you're in, but reading up on the regulations by the state agency governing repair shops would be very good. Here in Calif we have the Bureau of Automotive Repair(BAR) which is a division within the Consumer Affairs dept.

Make sure to keep all paperwork generated by the first shop. You will need that. Paperwork is key in court.

Odds are, it'll be a bit of a gamble in that you'll have to pay another shop quite a bit to correct issues. Hopefully in court you'll be able to get a judgement, and then collect on that judgement.(not always easy). Finding a shop might be tough. Shops can be reluctant to take on a job that is trying to track down all the mistakes a previous shop made. It's truly a can of worms at that point. And if they miss something they're now on the hook.

Calif BAR has a very short booklet that every consumer, regardless of the state they live in, should read. It's called "Write it Right". It was intended for service people doing the paperwork, but consumers should read to make sure the work order they are about to sign, well, should be signed, or needs to have the wording fixed.

 

Yes we are in California. I am enough of a hobby machinist I have most of the measurement tools and experience to figure this out. My friend is not interested in legal stuff at this point not throwing time and $$ after this at a second shop. The few people he has contacted don't want to touch it for the reasons you mentioned.

For those who have rebuilt this motor is there anything captain obvious that you would forget to assemble that would cause oiling issues like this.

I think regardless of what it is, beyond missing an oil pickup tube, its going to be pull the motor again type of activity.

 

Well, it’s probably a good idea to do a Leakdown test first. At least you’ll have some idea of what you’ve got to work with. Then pull the pan and valve covers and take some bearing caps off both a main and connecting rods, along with some cam shaft caps and see if there’s visible damage. It is passes a visual you can then plastigage the main and connecting rods bearings to see if they’re sized correctly. This may/or may not address the root cause, but What’s a bit scary is if you do have oil starvation just how long did it run like that. At least this initial inspection will help give you an idea if damage has resulted.

Depending on what you find, you might end up talking with a BAR rep by the time you’re done with this stage. BAR field people aren’t ignorant about cars. They know their ˟˟˟˟˟. They have the same certification (ASE’s) that a certified master tech has.
If this an actual licensed/permitted repair shop getting the BAR involved is almost a civic duty to help protect future consumers. Skilled techs actually resent those out there doing their chosen trade a disservice. But this advice is only dependent on what is uncovered.