1994 Chevrolet Truck

I have a 94 Chevy S-10 4.3L w/ 146000 miles. A few months ago, my car began stuttering. When I would drive and maintain a certain throttle level, the car would jerk and the engine would backfire. If I opened the throttle all the way, the car would jerk forward, backfire, then take off. The Next day I replaced the fuel pump. This did not fix the problem. A few days later, the weld between the muffler and catalytic converter cracked, and the muffler fell off, causing the catalytic converter to hang down. I noticed that the stuttering/stalling was gone. Yesterday I hung the catalytic converter back up with some wire, and now the stuttering is back. I was thinking it was a compression problem, or maybe a oxygen sensor problem, but my knowledge is limited. Any help would be greatly appreciated.
January 10, 2007.

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