engine problems

Hello,
I have a chevy blazer 95 with a 4.3 liter engine about 68k miles. For sometime now i can sligthly hear the lifters when i accelerate greatly but when i drive normally the sound is gone. One time i parked my car and went home to go to sleep and the following morning when i started the car it felt as if only two cylinders were working and it shook greatly. Also when i switched to neutral it could not reach 3000rpm which normally it could. When i took it to my mechanic he ran several tests on the compression of the engine and he said it was 90-120. They also told me that it isnt the catalytic converters fault. They are suggesting that i replace the engine.

Any Ideas?

Thanks in advance.
P.S. Maybe is important - beffore the prpblem, to the tank was added 1Quart alcohol. Crankshaft sensor is new,instaled after problem.

i beleve you have a cpi, which means its time to replace the nut kit, you also should check your fuel pressure

When you are accelerating, you are hearing pinging, not the lifters.

In your situation, this is caused by a plugged cat.

Also, check your oil for the strong smell of gas.