I have my buddy's 01 Extreme Blazer in my garage right now. It needed a pump (no start, no noise from the pump). We put a pump in it and got it to start, but now its running extremely rough. Idles rough, revs rough, whether hot or cold.

Fuel pressures at right around 59-60 psi while running. With just the key on it goes to around the same then after the keys turned off it drops down a bit to around 45-50 in about 20 minutes of sitting with the guage hooked up. Problem?

It also threw three codes: P0155 O2 sensor heater circuit malfunction, bank 2 sensor 1........P0135 O2 sensor heater circuit malfunction, bank 1 sensor 1.......P0300, which we all know the meaning of...

Any ideas? Am I looking at a fuel problem or a spark problem? 135k on the truck, plugs and wires were done in the last 2 years. Please help me out! My buddy needs his truck and I need my garage!

 

No ideas/opinions folks?

 

Not sure if you have located these:
P0135 - HO2S Heater Circuit Bank 1 Sensor 1
P0155 - Heated Oxygen Sensor Heater Circuit (bank 2, sensor 1)
P030x - Random/Multiple Cylinder Misfire Detected

Other than that, have you checked out the plugs, wires, cap & rotor?