I have a 97 with 4.3 liter. Keep getting codes po171 and po174. Truck starts immediately and is running better than ever. Idles very smooth. Have replaced fuel pressure regulator, fuel filter, and all of the ignition system. Cleaned MAF sensor and checked for vacumn leaks with carb cleaner and propane. Fuel pressure before the filter is 72psi. Fuel pressure at the test port is 50psi at idle and about 52 when applying throttle. Fuel pump leakdown is good. Can't figure this one out as the truck runs better then new. Any help would be appreciated. Need to get rid of codes to pass inspection. Thanks

 

usually when you have a double lean code like that theres a air leak in the intake system. can sometimes be a easy fix. if you have that engine with that little plastic hat that twists onto the throttle body, if that gasket is torn it can throw that code. check all your plastic lines going into the rubber boot for rips or cracks, same goes for the boot itself , make sure your air filter is clamped down properly

 

When those two DTC's are set together, the first thing to check is fuel pressure and leakdown. GM does not publish any "engine running" fuel pressure specs for this engine. All readings are taken with the engine off. Pressure and leakdown readings must be taken at the service port next to the distributor, AND at the fuel filter outlet. When checking at the fuel filter, the pressure tester must be connected directly to the filter, all fuel pressure and flow must end at the tester, and not allowed to the engine. Pressure readings are taken with the ignition in the RUN position, engine OFF, and the fuel pump running. At the service port, pressure must be 60psi to 66psi, and it must remain above 55psi for at least 10 minutes after the pump shuts off. At the fuel filter, pressure must be 73psi to 108psi, and it must remain above 55psi for at least 10 minutes after the pump shuts off.

Post your readings.

 

Added a bottle of Seafoam to the tank a couple days ago. Cleared all codes. Drove about 40 miles and no check engine light. Vehicle passed inspection today with no problems. Light is still off, were it previously would have come on after about 5 miles. Guess injectors were dirty. Thank you all for your input. Great forum.