Mechanic's Tunnel Vision: Diagnosing an Intermittent Stall on a 2009 Dodge Challenger

The Intermittent Stall Mystery

• 🎯 A 2009 Dodge Challenger with only 9,000 miles stalled unexpectedly after an exhaust system installation.
• 💡 The initial diagnosis focused on the fuel pump, as it wouldn't prime and the car wouldn't start after stalling.
• ⚠️ The car's behavior was intermittent, stalling and then refusing to start, only to start and run fine later, frustratingly making diagnosis difficult.

Diagnostic Process and Equipment

• 🔬 The mechanic used an oscilloscope to monitor voltage and current draw of the fuel pump during cranking.
• 📈 Initial tests showed the fuel pump drawing current but not receiving voltage when the car wouldn't start, leading to the assumption of a faulty pump.
• 🛠️ A scan tool was used to check for diagnostic trouble codes, revealing issues like "Torque request signal side" and "Remote key battery pull or battery low," but no direct fuel pump control codes.

Unraveling the Tunnel Vision

• 🧠 The mechanic realized they had "tunnel vision" fixated on the fuel pump, neglecting other possibilities.
• 💡 A crucial test involved removing the fuel pump relay to see if the car would stall and if a code would be set.
• 📉 Surprisingly, the car continued to run on residual fuel pressure even after the relay was removed, indicating the stall was not due to a fuel pump failure.

Key Learnings and Next Steps

• ✅ The diagnostic effort confirmed the fuel pump and its control circuit were not the cause of the intermittent stalling.
• ⚠️ The mechanic acknowledged the wasted effort due to the initial misdiagnosis but emphasized the learning experience.
• 🔍 Future steps include checking service bulletins, looking for similar issues on platforms like Identifix, and preparing to gather more data if the problem reoccurs.
• 💬 The mechanic plans to discuss the findings with the customer and drive the car to try and replicate the issue before further diagnosis.

Bonus Finding

• 📌 A "Fuel pump control circuit open" code (627) was eventually found, though it did not help diagnose the current issue, it confirmed the system's ability to monitor the control side.