1. 130
2. 135
3. 145
4. 100
5. 150
6. 150
7. 140
8. 150

Car has 212K miles on it. Keep in mind I'm in Colorado at 6000' elevation, so compression tests read lower than normal here. I'm totally cool with 130-150psi. But that being said, 100psi on cylinder 4 is not good.

I added oil and tested it again and it only went to 108 psi.

Wishful thinking, but could it be something as simple as a bad valve seal? Or is it likely valves?

I just bought the truck, everything else seems pretty good (paid $2500). It needs brake pads, maybe rotors, possibly fuel pump (has trouble starting when fuel is low). All of those are pretty easy and inexpensive though.

Keep it or flip it?

 

A bad valve seal is not going to cause low compression. Could be bad rings could be bad valve could be worn camshaft could be a bad lifter.

Does it run rough or does it run okay?

 

It runs great. I only did the test because it's a new purchase and I wanted to check it.

The fact that oil didn't really help more than likely indicates a problem in the head, not the block/piston, right?

Thanks!

 

Low compression is valve or rings worn. Is the air pressure going into the crankcase? Pull oil fill cap, to find out.

 

I'd run it unless...
oil consumption is excessive
smoke is excessive
that plug fouls up frequently
you can't pass emissions inspections

 

another possibility could be a worn cam lobe?

 

How about doing a leak down test? That is going to tell you more and help you with your decision. If you don’t have one, or have access to one, some auto parts stores will rent, or loan them out.

 

I'm gonna run it.

It doesn't use oil.
It doesn't smoke at all.
Plugs seem fine (haven't had it long though)
passed emissions just fine.

If it comes down to it, I've been wanting to do a LS rebuild anyway. It pulls strong, sounds good and seems healthy, so I'm gonna rock it.

This guy gives me a lot of inspiration : D (Tacoma 5.3 truck motor rebuild and swap)