1990 Lumina 2.5L backfiring?

today my car was extremely tempermental on me, stalling sometimes but mainly when I shut off engine it would not wanna start and would frequently backfire at the same time engine died when trying to start engine. After quite a while of trying to get it started, it would miraculously start up normally and I could go again for a while until I shut off engine whereupon it would do same thing all over again.

I have taken a tester to the plug under the dash and got codes 13 and 44 which are oxygen sensor related codes from what I understand.

I havent been able to replace O2 sensor yet and am wondering if I might also try looking elsewhere for other problems linked to the backfiring or if said backfiring is caused by O2 sensor problems. Any information would be helpful on this.

By the way, it currently has approximately 217,930 miles on it, uses no oil between changes and also has no coolant issues. I am somewhat impressed with this car even though I am not a true chevy fan.

That's a TBI motor. Take the lid off the air cleaner and see what the injector is doing when this happens. If no spray or seem to randomly spray a bit and stop, the ignition control module or coil pickup may be the problem (it times the injector pulses too)...if it's dumping fuel like a showerhead, the coolant temp sensor could be bad and telling it to go full rich when not needed.

I'm betteing the o2 sensor codes are symptomatic rather than the cause...o2 sensor shouldn't keep it from starting...

Heat soak ignition control modules and coil pickup failures were common on the 2.5...they ran hot back there close to the engine in the FWD configuration they didn't get much airflow...could even be a bad coil for that matter, old as it is...

when I check for spark at the plug, what is the best way to check that if I am alone? (if possible) - after it warms up more sunday I am gonna be doing other diagnostics as well