Bad compression 3 cylinder
 

Good morning friends, I recently bought a Ford F150 Lariat XL with engine 4.9 6L, the problem is that three cylinders of the engine have a very low compression (3 BAR) and the engine does not stabilize correctly. I have done the test of putting engine oil in the cylinder and retesting the compression and in this way, the compression is good. Then the segments are either stuck or broken. 1º.- If they are stuck, how can I release them? 2º.- If I have to remove the pistons, can I do it without removing the engine, taking out the crankcase and disengaging the cranks to remove it by the high part removing the stock? I appreciate the comments, greetings.

This caption explains how to do a compression test, and how to interpret the results:

https://www.supermotors.net/getfile/...-pressures.jpg
(phone app link)

I don't know what you mean by "stabilize", or what "segments" you're talking about. If the piston rings are broken, stuck, or damaged, the engine must be removed & either rebuilt, or replaced.

https://www.supermotors.net/getfile/...9lexploded.jpg
(phone app link)