Vehicle: 2003 Toyota Camry Sedan, L4-2.4L (2AZ-FE), Automatic Transmission/Transaxle

Mileage: 156,002 Miles

Problem: The customer had this vehicle towed to the shop. They stated it stalled at idle and would not restart. They also smelled fuel.

Case Details: The technician went out and started the engine in the parking lot. He didn't smell any fuel, so he brought it into his bay and let it sit with the engine idling. The engine began to surge a little and then stalled. It immediately started back up and would idle for a while (around seven minutes), then stall again.

The technician connected a scan tool and found no diagnostic trouble codes (DTCs) were set in the PCM. He hooked-up a scope to the crankshaft position sensor (CKP), camshaft position sensor (CMP), fuel injectors, mass airflow sensor (MAF), and coil IGT. He noted that before a stall occurred, nothing glitched or dropped out in the waveform.

Next, he watched short term fuel trim, air/fuel (AF) sensor voltage, RPM and the MAF sensor PID readings. To his surprise, right before the stall, the short-term fuel trim pegged negative, and the air/fuel voltage was at 2.3 volts.

He suspected the AF sensor was hanging up and causing the PCM to pull fuel from the engine causing the stall. He replaced the AF sensor but still had the same issue. He decided to add the rear O2 sensor voltage PID to the list and watched it. Right before the engine stalled, both O2 sensors went rich and the PCM sharply decreased fuel to the engine. The PCM was seeing an actual rich condition and was pulling fuel out. But why? Not sure where to go next with the diagnosis, he called ALLDATA Tech-Assist.

The consultant advised disconnecting the evaporative purge valve or pinching the hose closed to see if that corrected the stalling condition. NOTE: The purge valve doesn't start pulsing open until the engine has been running for 5 or 10 minutes. He said that if it does correct the problem, the charcoal canister could be loaded with raw fuel from overfilling the gas tank.

Confirmed Repair: The technician performed the test as advised and found the charcoal canister was full of fuel. That made perfect sense. When the evaporative purge valve opened, excessive fuel was pulled into the engine, the air/fuel ratio went rich, the PCM leaned out the air/fuel ratio and the engine stalled. The technician replaced the charcoal cannister. The overfill check valve's float was questionable and really didn't seal too well when the float was all the way up, so he also replaced the overfill check valve located on top of the tank. Interesting fix!