Experienced mechanic 93 jimmy-Appreciate your time!

I HAVE A 1993 JIMMY V6 4.3VORTEC AND THE FUEL PUMP WENT OUT! I WORK AT A DEALERSHIP AND WENT TO AUTOZONE TO GET THE FUEL PUMP, GOT IT PUT ON BY A TECH HERE, HE TESTED THE PRESSURE OF THE NEW FUEL PUMP AND IT WAS PINGING 100PSI, IT RAN FOR ABOUT 4-5MINS BEFORE HE SHUT IT OFF, SAID THATS WAY TO HIGH, SO HE TOOK IT BACK OFF, I WENT BACK TO AUTOZONE AND GOT ANOTHER PUMP, HE PUT IT ON, IT TESTED AT ABOUT 60PSI... NOW THE VEHICLE WILL SHAKE LIKE ITS ABOUT TO DIE AT IDLE BUT WILL NOT, WHEN IM DRIVING IT SEEMS FINE, JUST AT IDLE IT SHAKES AND IDLES ROUGH.. THE GAS MILEAGE IS CRAPPY AND THE EXHAUST HAS BLACK SMOKE COMING OUT SOMETIMES AND IS BURNING VERY HOT AND WHEN YOU LISTEN TO THE EXHAUST IT SEEMS AS IF ITS POPPING. DOES ANYONE HAVE AN IDEA WHAT IT COULD BE, NO CHECK ENGINE LIGHT, NEW PLUGS, SUPER CLEAN TRUCK, EVERY RECOMMENDED SERVICE HAS BEEN DONE ON THE VEHICLE SINCE NEW, HAS 99K ON IT.....PLEASE HELP!!:confused::confused::confused::confused: FEEL FREE TO CALL ME OR EMAIL ME AT ECLINE25@HOTMAIL.COM

OK, just curious, but lets see. You work at a dealer, you had a dealership tech install the fuel pump. You have a issue with poor/rough idle, sounds like its dumping fuel with the black smoke description and poor fuel economy. Why not have the guys you work with diagnose it?

I work at a Toyota Dealership, it being a 93, they dont have computer to test it, there is no gmc dealer around here. Just wondering if you have an idea of what it could be. thanks in advance for any thoughts!

did you check fuel presure before or after regulator?
sounds like fuel presure regulator is bad?

I didnt manually check it the tech did, i seen where he tested it at and it was on the back side of the motor in the middle so im not sure if that is before or after the regulator. I had another mechanic tell me sounds like the regulator, so i will try to replace it and go from there. Is the regulator hard to replace? Thanks so much for your help!

Fuel pressure is critical on these engines and they are real fussy when it comes to fuel pumps, they only like AC Delco and Delphi pumps. Stay away from aftermarket stuff, too many problems with them, (as you already found out).

If/when the fuel pressure regulator is subjected to more than 75psi, (you had 100psi) chances are real good that the diaphragm is ruptured. The regulator and injector are inside the plenum, along with two fuel lines that like to sprout leaks.

Key ON, engine OFF, fuel pump running, fuel pressure must be 55psi to 61psi and must remain above 50psi for at least 10 minutes after the pump shuts off.