First guess on a 2.2 Chevy?

[gmf]

'91 Cavalier, 155,000 miles. Turns over, spits sputters and back fires but won't start. Broken or stretched timing chain? Any guesses about a particular sensor it could be? Are these engine set ups famous for something going out? Someone mentioned to me a plug ya pull out of the catallytic converter. A plug? Were they talking about the O2 sensor? Any little bit of experienced forward thinking would be greatly appreciated. Thanks!

[Bubba B]

My first guess is it needs a new timing chain.