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Usually that is a sign of a broken timing belt or timing chain.
Timing chain slipped or broke
The year and engine size would help but you may have a bent valve or bent pushrod for # 4 cylinder if that is the only cylinder that has 0 for compression.
Never, it will last the life of the engine.
The chain will last the life if the engine and does not require changing.
You may have compression on any cylinder where the valves happen to be closed, but you will not have compression on all cylinders. 1991 Sable does not have a 305 engine.
If a timing chain broke, the engine wouldn't run and a compression test would read "0".
The engine would not run. The engine would lack compression.
Highly doubtful, the engine has a timing chain and the ignition relies on a crank sensor for timing. But if the chain did jump you could probably tell by doing a compression test.
Broken cam or timing chain is the most likely cause.
Factory recommendation is 90,000 miles. If it is a timing CHAIN and not a belt, it doesn't require changing. It should last the life of the engine.
No, timing chain doesn't need replacing.