Replacing Valve stem seals

2003 double cab, 3.4l, 4x4, automatic

started throwing a p0302 a while back, tried the usual changing the plugs, coils and wires, and running seafoam through the tank. Would clear the code for a day or two and it would come back.
Did a compression test at home, cylinder 2 producing 75 psi compare to the 150/160 of the others.
I havent noticed any blue smoke from the tail pipe and the truck runs with only a very small rythmic hiccup at idle.
Took it to a shop for further diagnosis and borescoping.
Mechanic also performed compression test with same results of 75 psi in cylinder 2.
Said valves were in synch and coming down in correct timing, yet there was some oil on the stem of the exhaust valve of cylinder 2. reported that the walls of the cylinder were clean and without damage, but there was a small buildup of some kind of sludge on the piston head of cylinder 2, closer to the exhaust side.
Also mentioned that the fuel injector for cylinder two was giving weird and inconsistent ohm readings from a multimeter, but told me that a bad injector wouldn't lead to a loss of compression.
Mechanic recommended to start by replacing valve stem seals, then checking the injector and if it was still an issue then look into piston rings.

I'm not the most familiar with the internals of valves, cams and all of that jazz, but I'm confident in my mechanical skill and believe that youtube can make a mechanic out of anybody so I'm going to attempt this job myself.

Do you guys agree with the diagnosis of valve stem seals?
What other parts and seals should i be replacing while I'm doing this job?
I read someone recommending to just save myself the trouble from the beginning and pull the engine and put it on a stand.

Thoughts, opinions, comments, and wisdom are all appreciated!

 

pic related it the piston head of cylinder 2. piston if perfectly clean except for this buildup on the edge.
sorry fo the poor quality as this is a picture of his phone taking a picture of a borescope screen.

 

Unfortunately, you need an engine. If valve timing is good and the head gasket is good there is no adding the compression back in and the code will keep coming back. Hate to see you do valve stem seals and an injector just to need an engine.

 

Did you find a video on how to do this on the 5vz without taking the head off?
I’m considering this too

 

I’ve seen a lot off these situations and it was the valve shims I believe the exhaust that are out of wack, Timmy did one where the compression was I’m thinking 90 psi and after the valve adjustment it went up to 175 or something

 

It's not too bad. You can use a cylinder leak tester to put pressure in the cylinder to hold the valves up or you can fill the cylinder with rope and turn the engine over to push the rope up to hold the valves. You need a special tool to compress the valve springs going back together though. Not sure space-wise on the v6.

 

okay that sounds pretty extreme. can you tell me why i would need a new engine, considering these symptoms.
I'm not 100% if the head gasket is good or not, but im really curious as to why you say the engine is toast.

 

Most likely getting coolant into cyl 2.

About a 50 chance of it being a head gasket or crack between the valves.

Engine Head Gasket / Cracked Head Repair (Toyota 3.4L V6 5VZ-FE ) - Part 4 (youtube.com)

 

Did the mechanic check the valve clearances with a feeler gauge? That'd be the SOP with low compression - the exhaust valves tend to get tight over time and burn out, although it's not as common in the 5VZ as it is in the 3RZ.

If it was a head gasket/coolant leak, I'd expect to see a "steam-cleaned" piston without any sludge. I think it may be a combination of worn rings and an exhaust valve or two out of adjustment. Hopefully you can get away with a valve adjustment and you don't need a new head.

 

Several months ago I started to lose alot of power from my Taco and had constant white exhaust. It seemed to have been getting worse and worse so I decided to buy a new truck to allow for downtime on my Tacoma which was my one and only daily driver but is now my project truck. Anyways to get to the point... without doing any compression test or diagnostics I just decided to go ahead and start taking apart my engine likely knowing what to expect.
Just this past week, I got to removing the intake manifold and the heads to find exactly what I expected but didn't hope for. Here are just a few of the many pictures I've taken of this project...

Currently I've got all but my heads cleaned up but I'm able to see the crack in cylinder 3 which is where that pool is in the picture above.

Seeing as how this is my project truck now, My plans are to replace both heads with rebuilt ones, and change out everything else I think might need changing; starter, alternator, water pump, engine mounts, knock sensors, fuel injectors, hoses, gaskets, etc

Trucks gonna get pieced back together and run better than ever.

 

I have no idea how he got to that diagnosis based on the information you provided. A leak down test would be the route I would go. I bet it's head related and not something so catastrophic to require a new engine haha.

 

Did he do a wet compression test?

I'd hate to see you do valve work and then it ends up needing a engine rebuild anyway