2.2 corsica won't start

1990 Corsica 2.2L I went to start it this morning, but all it would muster is some backfiring. I changed the spark plugs and checked the compression while I was at it.
The result...it still backfires but won't start. How do I trouble shoot from here? This car has always started very easily and runs well. Thanks in advance!
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backfiring.
timing belt.
Jim.J
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Checking spark, they -seem- ok from each wire. This car has a timing chain, but also has 300,000km Could it possibly jump a cog? Is there anyway to check other than removing the front cover? Oh, the backfiring is always through the intake. Richard

backfiring.
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Sounds like it's a timing chain issue. The 2.2 is bad about shreading the nylon chain tensioner; then the chain will jump 2 or 3 teeth. It's about a 3 hour job to replace it.

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OK, I ripped apart the front cover of the engine to find the car is in perfect time. I put it all back together again, and now it starts. Hmmmmm. Would contamination (oil or guck that I cannot see back there) on the cam/crank sensor cause a mis-time, or did the computer wack out on the timing for some other reason? Me thinks I need to visit GM and have them scan the computer if it happens again. rick

backfiring.
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It was the crank sensor

backfiring.
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