No codes in your OBD box? I would expect a bad 02 sensor to throw some code, even if it didn't directly say 02.

It's fairly easy to pull out all the injectors, still on the fuel rail. Then turn the key to 'on'. This should pressurize the system and you should see dripping if any injector leaks. Don't forget the cold start injector under the intake manifold. An easy way to eliminate that for testing is to clamp off the fuel line to it, but my old line was split when I took the clamp off, so be careful.
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Andy in St. Paul. '89 244 147K mi, '91 745 Regina 202K, '87 245 lost to rust at 225K