1998 Chevy Truck fuel delivery problem, I think

https://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm
Go here and checkout our video.
You can rent the test gauge at Autozone.
Be aware that GM advises to use only top tier detergent gas, from top tier suppliers, this keeps injectors clean. You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs! Last tune up was? Air filter?

I'll be here!

174 is a lean code, it is not an O2 code! Did you check for a vacuum leak yet? Also check the injectors, if it seems to misfire. And the MAF especially if you use an oil type replacement air filter is suspect!

TESTS W/CODES - 5.7L -1998 Chevrolet Pickup K1500
Page 1 of 2

NOTE: For circuit reference, see WIRING DIAGRAMS - 5.7L article.

DTC P0174 - FUEL TRIM SYSTEM LEAN BANK 2
Circuit Description
A "closed loop" air/fuel metering system is utilized for driveability, fuel economy and emission control. While in closed loop, VCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change in fuel delivery can be monitored using a scan tool and is indicated by Long Term (LT) and Short Term (ST) fuel trim values. Ideal fuel trim is about 128. If a lean condition is present, VCM will increase fuel, resulting in a fuel trim value greater than 128. If a rich condition is present, VCM will reduce fuel, resulting in a fuel trim value less than 128. DTC will set if an excessively lean condition is detected.
Conditions for setting DTC:
à   No ECT, EGR, EVAP, HO2S, IAC, IAT, MAF, MAP, TP or VS sensor DTCs are set.
à   No misfire DTCs are set.
à   Throttle position is less than 69.9 percent.
à   Engine speed between 575-4000 RPM.
à   BARO is greater than 70 kPa.
à   ECT 167-237 °F (75-114 °C).
à   MAP 22-85 kPa.
à   IAT 46-169 °F (-8.3 to 76 °C).
à   MAF 3-85 gm/s.
à   Vehicle speed is less than 85 MPH.
Diagnostic Procedures
1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK, then go to next step. 2. Check for the following conditions:
à   Exhaust system for corrosion, loose or missing hardware.
à   HO2S is securely installed and pigtail is not contacting exhaust manifold or ignition wiring.
à   Vacuum hoses for splits, kinks and proper connections. Throttle body, intake manifold and EGR for vacuum leaks. See Fig. 1 -Fig. 3.
à   IAC, if a high or unsteady idle is being experienced.
à   Crankcase ventilation valve, spring and "O" ring for proper installation.
à   Fuel for excessive water, alcohol or other contaminants.
à   VCM and sensor ground are clean, tight and in proper locations.
If a problem is found, go to step 8). If no problem is found, go to next step.

8/15/2008
TESTS W/CODES - 5.7L -1998 Chevrolet Pickup K1500
Page 2 of 2
3. Connect a fuel pressure gauge to fuel rail fitting. Turn ignition off for 10 seconds. Turn A/C off. Turn ignition on. Fuel pump should run for about 2 seconds. It may be necessary to cycle ignition on more than once to obtain maximum pressure. Note pressure with pump running. On CSI models, pressure should be 60-66 psi (4.2-4.6 kPa). On SFI models, pressure should be 56-62 psi (3.9-4.4 kPa). On all models, when pump stops, pressure may slightly vary, but should hold steady. If pressure is as specified, go to next step. If pressure is not as specified, go to step 11). 4. Start and idle engine at normal operating temperature. If pressure decreases by 3-10 psi (.2-.7 kg/cm2 ), go to next step. If pressure does not decrease by 3-10 psi (.2-.7 kg/cm2 ), go to step 11). 5. Perform injector balance test. See SYSTEM/COMPONENT TESTS - 5.7L article. If a problem is found, go to step 9). If no problem is found, go to next step. 6. Perform canister purge solenoid check. See SYSTEM/COMPONENT TESTS - 5.7L article. If a problem is found, go to next step. If no problem is found, see DIAGNOSTIC AIDS. 7. Repair EVAP system. Install scan tool. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to step 10). If values are not as specified, see DIAGNOSTIC AIDS. 8. Repair problem as necessary. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to step 10). If values are not as specified, go to step 3). 9. Replace fuel injector. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to next step. If values are not as specified, go to step 6). 10. Lean condition is not present. See TESTS W/O CODES - 5.7L article. 11. Diagnose fuel system. See BASIC TESTING - 5.7L article. After repairs, go to next step. 12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2). 13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
Diagnostic Aids
If problem can not be isolated during diagnostic procedures, monitor LT fuel trim value while operating vehicle under various load conditions. A condition that causes DTC P0300 may also result in DTC P0174 setting. Also, an extreme lean condition that may cause DTC P0174 to set may result in P0300 setting due to misfire at idle. If cause for DTC P0174 can not be determined and DTC P0300 is also set, go to DTC P0300.

8/15/2008
You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!

Myself, I would use an air impact and remove the two staps holding the tank, with a floor jack under it! Drain it down to within one gallon of empty, remove the connections and remove the tank, use a spanner wrench or a brass punch and hammer and remove the lock ring, R & R the pump and reinstall the tank.