This site is an awesome resource but I haven't found a solution for my problem. I am a mechanic/fabricator by trade and I am baffled! Here is the whole story...
The motor was running great, then it developed a squeak that seemed to be from the bottom end. I changed the oil since it was due and the first time I started my truck after the oil change the squeak turned into a knock until it built oil pressure, and then turned back into a squeak. So at this point I'm bummed because I feel like I have a bad bearing in the bottom end but I continue driving it. Runs fine but seems a little low on power. I put 100 miles on it or so and then got some gas. 13 miles after getting gas the engine just dies on me while I'm driving. No bad noises, just dead and wouldn't refire. I get it home thinking timing best flew off but no, it's still there and the timing marks are all lined up still. Confirmed spark. Confirmed fuel. Checked compression. All were between 160-180 PSI but funny stuff happens on both rear cylinders while doing the compression test. I start cranking and the gauge with go up to around 20-40 PSI and not move for 3-4 more revolutions and then spike up to 185 on one and 200 on the other. It doesn't even try to start. Turns over fine but with a squeak. Plugged in scan tool and there are NO DTC. WTF!!! Nothing makes sense. I don't know why a squeak would prevent it from running? If it is bad gas how could I drive for 13 miles and not be able to start it with starting fluid? What is up with the compression on the 2 rear cylinders? I really don't want to tow it to a Toyota Stealership. Any input is appreciated.

 

Piston Ring(s) went out? Bent rod(s) possibly as well. That's my guess based on what it sounds like. If you can get an inspection camera with a light in there, and check the walls of the cylinder, I think you'll know for sure then.

Edit: Are the valves opening up at all?

 

I don't feel like the rods could be bent or the rings being bad if it gets good compression. I took both valve covers off and checked the cams and valve clearance and confirmed everything is moving properly. It all looks good.

 

So I took it to the dealer out of frustration. They called and said, sorry it needs a new motor. I asked why? They said motor has no compression. I called bull˟˟˟˟ since I did a compression test and all was good for the most part.
So they called the next day and told me the timing belt tentioner exploded which caused the horrible squeak and no running. Doesn't need a motor.

 

Good thing you'd done a compression check and knew enough to call bullsqueakers....
Glad it wasn't internal and that it's non-interference.
thanks for updating!

 

Sad you got a bad call from a dealership shop. Not all dealerships are bad. It's the technician. Some good and skilled some bad.
Timing belt tensioner bad can be the noise and the non-start. It could explain the compression also if the timing belt jumped.
Glad it wasn't what I've seen in the past..... 3.4L are notorious for throwing the thrust washer shims usually from a torque converter problem excessively pushing on the flywheel.

 

So easy to pull that top timing belt cover !!

Since both the Crank and Cams were turning those two sensors won`t show a error .

Just curious how many miles on the engine ??

 

That's awesome it got figured out! The Tensioner, it all makes so much sense now.