Backfires when I give it gas when it was up - 1994 GMC Jimmy

exhaust restricted////catalytic converter or muffler

probably one of the coils. There was a major recall for 4 and 6 cyl engines with faulty coils.

I’m happy to assist further over the phone at https://www.6ya.com/expert/howard_977676954994c5b2

Has anyone checked base fuel pressure with a gauge ?

Fuel delivery problem, not enough fuel on acceleration could cause backfires. Many things cause backfires, mechanical and electronic. I need more info to give a better diagnosis. Did the problem happen all of a sudden or has the vehicle been running crappy for awhile.

Backfiring occurs when uncombusted gasoline gets into the muffler. You will have to figure out if the engine is flooding and why (can be a lot of things - poor ignition, problem with fuel pressure regulator or an injector, vacuum leak, etc.). Existing trouble codes (DTCs) will help you diagnose the problem.

Check timing yet? Try advancing it slightly a few degrees.

you might have a blocked catalogue in your manafold systrm

ITS COULD BE A PLUG FUILTER OR IT,'S JUST JUMP TIME AT THE TIMMMING BULT. OR THE DIUSSDEPTER MOVE...

it is the fuel pressure most likely have the fuel pressure checked

Have the throttle position sensor checked, might be faulty.