96 3.0L XLT, 4x2 Automatic.
Past few days on start up truck has idled rough like it was misfiring, evens out after a bit and ran fine. Today I was burping the coolant and the engine made a click noise, engine stumbled and misfired a bit and returned to normal. Another click noise and the engine dies. No start, fuel pump cuts on, there is fuel pressure at shrader valve. I removed a few spark plugs and cranked the engine and they fired. The engine does turnover (spins not start) but sounds very fast and uneven, backfires. Smoke comes out of intake. Concerned maybe timing chain snapped? The truck ran very well only a week ago. Only issue I was dealing with before is the engine never heated up all the way even with a new thermostat. Any advice appreciated.

 

First thing to do is a compression test.

 

So I'm getting pretty low compression
65psi. 60psi
75psi. 95psi
70psi. 60psi
On their respective cylinders. Also, while trying to crank the engine sometimes it seems to abruptly stop. The battery is getting low with these attempts, I've had to charge it once already, but could it be trying to seize up?

 

try again with a good charged battery with all plugs out.

 

And throttle held wide open.

 

I didn't get another pressure test before I stupidly decided it must be the timing chain and tore everything apart. So, it's not the timing chain... While waiting for OEM parts to replace the timing chain and water pump since I'm there I scoped all 6 cylinders. All of them look brand new, no carbon even. Except cylinder 6 which has a milky white substance on top of the piston. I'm guessing head gasket. That wouldn't be enough for a no start though would it? Anyway, as for all the cylinders being so clean l, I've heard that can be a blown head gasket too due to steam cleaning, but for both head gaskets to blow... Seems unlikely. Truck ran fine a few days ago. Also all the plug tips were wet with gas. Wish I hadn't listened to reddit about the timing chain now.

Cylinder six

Cylinders 1-5 look like this.