1994 Ford Taurus 3.8L Fuel Injector Driver Circuit Fault: Diagnosis and Repair Options with PCM Readings
I own a 1994 Ford Taurus with a 3.8L engine, currently at 150,000 miles. After installing a remanufactured Powertrain Control Module (PCM), I noticed inconsistent readings on the fuel injector driver circuits. The new PCM shows 11.88 MΩ on five of the six circuits and 0.455 KΩ on one circuit when measured directly at the PCM connector pins. In contrast, the original PCM displayed 12.25 MΩ on five circuits and an open (no reading) on one circuit under identical conditions. The question is: Can the fuel injector driver circuits be repaired or replaced? Are these internal to the PCM, or could there be a wiring issue between the injectors and the PCM? I’ve already tested the injector harness at the transmission bell housing with the main engine harness disconnected. Results: - Power wire (red) to each injector: 15 ohms - Red power wire to ground: open (no reading) - Injector wire to ground: open (no reading) - Injector wire to injector wire: 29 ohms I’ve also tested the PCM connector with the module disconnected, key off: - All pins show ~12.1 volts when measured to battery negative. - Voltage readings to positive post vary from 70 MV to over 150 MV (e.g., pin #39 fluctuates between 129–120 MV). - Resistance from PCM connector to battery terminals: all at ~7.4 KΩ. I’ve also verified that the red common power wire is functional and that there’s no open or short in the injector harness. However, when back-probing ground circuits at the PCM (pins 40/60), I observed inconsistent voltages—12V on one pin, 5V on another—which led me to suspect a grounding issue. I’ve since replaced the PCM and driven the vehicle for 50 miles. The engine runs normally now with no fuel delivery issues. However, I’d like to understand whether the original fault was due to a faulty PCM or a wiring problem in the injector circuit that could have been repaired before replacement.
The fuel injector driver circuits are internal to the PCM. In most cases, replacing the PCM is the standard solution. You may contact a reputable PCM remanufacturer to inquire about available repair or replacement components. Before proceeding with a new unit, ensure there’s no fault in the wiring from the injectors to the PCM—such as open circuits, ground faults, shorted wires, or excessive injector current draw. These issues can cause false readings or prevent proper operation. I recommend using a remanufactured PCM—search for 'PCM remanufacturers' on Google. In most cases, cost versus time and learning makes this the more practical option. Also, ensure any replacement unit comes with warranty support.