Chevrolet Repair: Injector miss fire, fuel inj, compression gauge

Question
hi.. i have a 2004 chevy colorado with 3.5l engine,have fault code p203 and 303 for cylinder #3. i have replace coil pack and all spark plugs and also the fuel injector for #3 cylinder. i have checked the wire harness only from the inj to the back of engine where it plugs into  main harness. i still have engine miss fire and not running good. i have no access for any wire schematics or any way to test the ecu. do you have any ideas or advice that i may have not tryed?? thank you.

Answer
HI JASON, OK WHAT I WOULD DO IN YOUR SHOES IT GET YOURSELF A MARKER LIGHT BULB, #921 GO TO THE PART STORE GET ONE COST YOU ABOUT $1.25 OR REMOVE THE LIGHT BULB FROM YOUR LICENSE PLATE LIGHT HOUSING. THIS SHOULD BE A 194 OR 921 BULB. BEND THE TABS STRAIGHT OUT AND REMOVE THE INJ PLUG HARNESS THAT IS NOT FIRING ON THAT CYLINDER. PUT THE LIGHT BULB WIRES IN EACH SIDE OF THE FUEL INJ HARNESS AND START IT UP..THIS LIGHT SHOULD BE GOING ON AND OFF. THIS IS CALLED A PULSE. THIS COMES FROM THE PCM..IF NO PULSE HERE, EITHER THE PCM OR WIRING HARNESS IS BAD...BUT LETS SAY THERE IS A PULSE AND YOU KNOW FOR SURE YOU HAVE IGNITION [SPARK AT THAT CYLINDER] THE ONLY THING LEFT IS INTERNAL PROBLEMS SUCH A BAD VALVE...IF THIS IS THE CASE GET YOURSELF A COMPRESSION GAUGE AND TEST THAT CYLINDER..SHOULD HAVE ABOUT 150 LBS OR SO + OR- 25 LBS. I DO NOT KNOW HOW YOU HAVE CHECKED THE INJ HARNESS FOR A PULSE ?? LET ME KNOW IF THIS DOES NOT HELP YOU,,GOOD LUCK,TOM..