1998 K1500 5.7L Engine P0171/P0174 (Pending) - Lean Fuel Trim Issues and Low Fuel Pressure Diagnosis
Diagnostic information from Torque app (web lookup): System: Powertrain - Fuel and Air Metering - ISO/SAE Controlled Description: Fuel Trim System Lean Conditions Location: Bank 1 Cause: - No active PCM fault codes set. - ECT (Engine Coolant Temperature) input ranges from 176°F to 230°F. - Engine speed between 1000 and 4000 RPM (up to 4000 RPM based on VIN). - Throttle angle remains steady below 91%. - Vehicle speed sensor (VSS) reading under 70 mph. - Purge duty cycle below 80%. The Powertrain Control Module (PCM) detected either: - Long Term Fuel Trim (LTFT) exceeding 100%, OR - Short Term Fuel Trim (STFT) falling below 94% for a sustained period of over 25 seconds. Fuel pressure check results: - Cold start (KOEO): 55 psi. - After 5 minutes, fuel pressure dropped approximately 2 psi. Question: If this is a fuel pressure issue, why does the fault code first appear on Bank 1? Attached screenshot: screenshot.jpg (247.38 KiB) - Viewed 351 times
Your Long Term Fuel Trim (LTFT) values are high, and fuel pressure is low — this strongly suggests a fuel pump issue. The fact that Bank 1 is reporting the fault first indicates higher fuel trim readings on that bank, which aligns with lean conditions. Note: This diagnosis is currently theoretical. An injector cleaner may help improve performance but will not resolve underlying low fuel pressure. Recommendation: Try replacing the fuel filter — it is still frame-mounted in 1998 K1500 models. If replacing, I recommend installing an OEM-quality fuel pump for long-term reliability. PS: Your ECT reading appears low in the snapshot — please confirm whether the engine will warm up properly under normal conditions.