A 2007 Ford F150 XLT is experiencing hesitation and misfire issues. A scan tool reveals a potential fuel pump fault. This article outlines diagnostic steps taken using a scan tool and lab scope to pinpoint the problem within the Ford’s FPDM fuel system.
Diagnosing a 2007 F150 Fuel System Problem
The truck exhibits a slightly rough idle with minor misfires detected across all cylinders during a cylinder contribution test. Hesitation is pronounced under wide-open throttle (WOT) conditions. Notably, the only diagnostic trouble code (DTC) present relates to a generator fault, potentially impacting voltage stability. A voltage reading of 13.3V at idle was observed.
Initial scan tool diagnostics, with a vacuum line connected to the Fuel Rail Pressure Sensor (FRPS), revealed consistent fuel rail pressure between 37-39 PSI at both idle and WOT. However, a pressure spike to 49 PSI occurs upon releasing the throttle after a WOT run. Simultaneously, the upstream oxygen sensors (O2) transition from a normal reading to a pegged rich condition only when the FRPS hits 49 PSI. Interestingly, a momentary lean condition is registered by both upstream and downstream O2 sensors at the initial throttle application.
Further investigation involved using a lab scope to analyze the Fuel Pump Driver Module (FPDM) fault return signal (PIN 30) and the PCM to FPDM control signal (PIN 62) at the PCM connector. The FPDM return fault signal consistently showed a 50% duty cycle, suggesting no fault. However, the PCM to FPDM control signal exhibited a decrease from 86% to 67% with increasing engine load. This contradicts the expected behavior of an increasing signal with higher load. This raises the question of whether the signal interpretation should be inverted, with 86% on the lab scope representing a 14% command to the FPDM.
Understanding Ford’s FPDM Fuel System and Potential Issues
The normal operating fuel pressure for this system is considerably lower than other systems, typically around 28-35 PSI Key On Engine Running (KOER). The observed pressure readings of 37-39 PSI at idle and WOT, along with the unusual pressure spike to 49 PSI, warrant further investigation.
A common issue in these trucks is corrosion within the FPDM. While the observed symptoms don’t definitively point to FPDM failure, it remains a possibility. A mechanical fuel pressure gauge reading could provide a more accurate assessment of fuel pressure under load.
Next Steps in Diagnosing the F150’s Fuel Problem
Further diagnostic steps include:
- Verify Generator Output: Confirm stable voltage output from the generator under load to rule out voltage-related issues affecting the fuel system.
- Direct Fuel Pressure Measurement: Install a mechanical fuel pressure gauge to compare readings with scan tool data and confirm accurate pressure readings.
- FPDM Inspection: Visually inspect the FPDM for signs of corrosion or damage. Consider testing the FPDM directly.
- FRPS Testing: Evaluate the FRPS for proper operation as its readings are crucial for fuel system control.
The diagnostic process is ongoing. Determining the root cause of the hesitation and misfire will require further testing and analysis of the FPDM, fuel pump, and related components.
