Engine Performance problem
1997 Oldsmobile Bravada 6 cyl All Wheel Drive Automatic 102000 miles

qUESTION IS DUE TO MY OWN STUPIDITY OF ADDING YR OLD GAS FROM BOAT. WOULDN'T START, FINALLY BURNT OUT ALL BAD GAS, STILL BARELY RUNS, REPLACED 4 O2 SENSORS, CAT, MUFFLER TAILPIPE, PERFORMANCE THE SAME. HAD PRO CLEANED EMISSION SYSTEM DONE MISFIRE CODES OF PO300 ALONG WITH 137 AND 143. NO IMPROVEMENT, NO POWER, #3 CYLINDER IS MISFIRING LIKE CRAZY, COMP TEST OK, FUEL PRESSURE AT 40 + CAT GOT SO HOT MELTED CASING AROUND GAS TANK (THE REASON FOR REPLACING) CHECKED FOR VACUUM, NEW GAS FILTER, PCV. EITHER PLUGGED INJ OR SOME OTHER COMPONENT LIKE MAP (CLEANED) SHORT, PGR VALVE, IAC COULD BE CAUSING BUT AS CAR IS WORTH AT MOST 3 GRAND, I HESITATE TO PUT 1200 IN A FUEL INJECTOR HARNESS AND BOOKS SAY DO NOT REPLACE JUST THE OFFENDING ONE. IDLE ROUGH, NO POWER, TAKES FOREVER TO GET TO 50 MPH, SERV LT INTERMITTENTLY BLINKS BUT ONLY GOES AWAY IF i DISCONNECT BATT OR PULL FUSE. CURRENTLY RUNNING BEST FUEL PREM. WITH THE CLEANER SHOP PUT IN OIL AND GAS. i AM GOING BROKE IN CLEANERS, BOUGHT A MULTITESTER TO SEE IF i COULD ISOLATE SOME EMISSION COMPONENT AT FAULT, BUT HAVEN'T GOT TO IT YET. RAN BEAUTIFULLY BEFORE BOAT GAS FUBAR, BUT WAS STUCK IN THE WATER W/O POWER TO RETRIEVE IT OUT. i NEVER WOULD HAVE USED THAT GAS BUT AT 4 BUCKS A GAL IT WAS 120 BUCKS WORTH. SO FAR I AM APPROACHING 1000. IN REPAIR. I WRITE THIS SO OTHERS DO NOT OUT OF DESPARATION BURN THEIR FURNACE OIL IN HOPES OF GETTING TO WORK. :.) THXS IN ADVANCE, ME? I AM LOOKING FOR A 50-60S SMALL V-8 TRUCK THAT I CAN STILL WORK ON. "ANOTHER REASON TO HATE OPEC AND FOSSIL FUEL CARS" "LEARNT MY LESSON LEE"
BTW IT HAS A V-6 4.3 LITER SYSTEM AND AS NEAR AS I CAN FIGURE A CMFI INJECTION SYSTEM
DEFINED BY THE W IN VIN WHICH CALLS IT CPI. WHICH I THOUGHT MEANT COMPICATED PUNISHMENT FOR IDIOTS. BUT REALLY MEAN COMPICATED MONEY PIT FOR IDIOTS. GIVE ME A CARB AND SOME GUMOUT SO I DON;T HAVE TO LEAVE MY SENSES AND STAY IN, WHEN MY MATE SAYS OUT.

40 psi fuel pressure isn't good. You should have closer to 50.
As for the CPI, the reason you cannot change just one injector is because you only have one. It feeds different cylinders through poppet nozzles.
However if you're only seeing a miss on number three and your SURE it isn't plug related you can clean the poppet nozzles. You just pull the CPI unit and soak the poppet nozzles in cleaner, then shoot some cleaner through them.

It is also possible that the fuel pressure regulator has failed. That could be dumping extra fuel into the engine causing the hot cat and muffler. You can follow the test procedure in the book and see what you get.
The regulator in attached to the back of the injector inside the intake.

Also you can buy a re-man spider unit from
http://www.lindertech.com/reconinj.htm
or
http://www.robstark.com/scpi.htm
for about 300 bucks.

You need to get a factory book and follow the testing/troubleshooting steps. The online ones at mitchell are pretty good and they are not that expensive either (compared to a factory set from Helm that will run almost 200 dollars)