Yeah definitely bad compression in atleast 3 of those cylinders. It may be worn or stuck piston rings causing the compression and oil usage problem.
How does your oil look? Does it darken pretty quickly after an oil change? It may simply be dirty with sludge.
Before you dump alot of money on a new engine, try to clean this one. Some oil additives may be able to help. I highly highly recommend Auto-Rx, which I believe is available in Mexico but don't quote me on that. This product cleans better than any other oil additive and does it in a way to prevent sludge breaking off and clogging oil galleries. The down side is it takes a long time for it to work (hundreds to thousands of miles).
For a quick attempt at cleaning up the engine, buy 1 can of Seafoam, 8 new spark plugs (Motorcraft or Autolite), and 6 quarts of Motorcraft 5W-20 or 5W-30 motor oil and a Motorcraft FL-820S oil filter.
Dump in half a can of Seafoam into the oil. With the engine hot and running, introduce the other half of the Seafoam into the PCV valve. I find that holding the throttle to about 1,000-1,200 RPMs and slowly pour it into the PCV valve works best - do not submerge the valve in it or it will not vaporize correctly. When it sucks it all up, turn off the engine and let it sit for 15 minutes. Start the engine and rev the engine up and down, mostly keeping it at mid-range RPMs. The mid-to-high RPMs help really force carbon out of the cylinders and off the rings. It will smoke ALOT. This is normal. When it mostly stops smoking, drive it around for about 10 minutes and then change the oil with fresh oil.
Wait until the engine cools off and then change the spark plugs. Do not change with the engine hot as they will not torque down properly and can cause thread damage. Only torque down to 16 lb-ft and do not use any anti-seize. You can skip the spark plugs if you've changed them recently, but it's a good idea to do them after a Seafoam treatment and they also may have alot of oil on them from the leaking rings.
Here's a friend's video of his Seafoam treatment through the PCV valve:
http://www.youtube.com/watch?v=yibMhMADJV8