1997 Ford Ranger 4.0L Fuel Trim % Reading -100.0: Cause and Resolution
My 1997 Ford Ranger with a 4.0L engine shows all normal sensor readings, but the ST FTRM (%) values are consistently displaying -100.0. The truck runs and drives perfectly, with no performance issues. I'm wondering if this is a legitimate fault or simply an anomaly in the scan tool reading. Can anyone confirm whether a -100.0 fuel trim percentage is normal for a healthy engine? Or could it be a software or hardware issue within the ECU or scan tool?
This is most likely a scan tool interpretation issue rather than an actual engine problem. A reading of -100.0 for fuel trim is outside typical operating ranges and may indicate a flaw in the scan tool's calibration or software. I recommend contacting the manufacturer of your diagnostic scanner to verify if this value is supported or if there’s a known bug with their device.