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With the plenum off, go to the fuel pump relay and jump the Orange to the Gray wire. Let the fuel pump run and visually look for a leak.
Also check the EGR valve to make sure it is not stuck open.
You need to make sure the fuel pressure regulator is not leaking on the spider also. Does the fuel system hold pressure??
The TPS should have a smooth sweap when checked with an ohm meter voltage should be about .5 closed throttle and about 4.5 WO .Thottle.
You can also check it with a scan tool.
Are you getting any sensor codes??
Are you sure about that EGR valve I see a lot of rich running problems related to stuck EGR's
Do you still have acces to the scan tool if so check the injector pulse width and ley me know what you get.
You describing a lean condition (popping on accel) and not knowing a fuel pressure or volume reading isn't helping. A misfiring engine due to a lean condition will result in unburned fuel entering the CAT and making it glow, just like a rich condition will. You could have a clogged CAT also; Try taking a vacuum reading.
And that EGR could be the cause of a lean condition also
Lean miss looking like a rich condition.
Should have a code but I would check to make sure.
Maybe it has a scratchy area that makes it hic-up But I'd would be eliminating fuel and air problems first.
Also found this while looking around one of my subscription sites:: 95 GMC SAFARI 4.3 W engine
Complaint: came in to our shop after being to another shop several times..originally for a fuel smell with no drivability concern. after the other shop replaced the injector unit and fuel line kit, the customer complained of a poor idle after warm up and still had a very strong fuel smell. Tech Notes: scanned for codes. engine had low vaccum (9lbs) ran rough . Tested for vac leaks by spraying carb cleaner around common leak areas, with carefull attention to intake area. lo leaks detected. injected propane into crankcase and test showed no intake leak. reccomended going in to the intake to re-ck work of other shop. intake interior wet but no puddles, van sat overnight before opening, may have evaporated. replaced injector and return and feed lines which looked like they werent replaced, but no physical sign of leak. after installation of new injector and lines, engine hunts and on accel, backfires through carb. fuel pressure good and vaccum good. checked egr using scan tool and computer would only switch egr to full or closed Fix Notes: found tsb relating to prom update when replacing egr tsb #57-65-22. replaced prom . problem solved