I have a 03 yukon xl with a 5.3, went the check engine light first came on the code was p0171 and p0174. I changed both of the pre o2 sensors, the check engine light went out and came back on after a week with a code of p0171. Changed the fuel filter, mass airflow sensor, air filter and add lucas fuel injector cleaner, the engine light went out for about 2 weeks. Now it is back on, I checked the operation of each injector according to the chilton manual, can anyone help me out?:mad:
