95 S-10 suddenly running rough

4cly 5 speed 95 S-10 has suddenly started running rough and hesitating, backfireing occassionally. Check engine light not on so can't use code reader to help. Changed fuel filter, plugs and did ohm check on wires. Unplugged sensors to see if it changed (only because that worked with the mass air flow sensor on my old T-Bird) to no avail except check engine light came on and had to clear error. I would think anything beyond these items would trigger an error code but not getting any. Any suggestions would be greatly appreciated. Thanks

fuel filter fuel pressure?