Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSFORD1990RANGER 4WD L4-140 2.3L SOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTIGNITION SYSTEMDESCRIPTION AND OPERATIONIGNITION DIAGNOSTIC MONITOR (IDM)
1990 Ford Ranger 4WD L4-140 2.3L SOHC
Ignition Diagnostic Monitor (IDM)
1990 Ford Ranger 4WD L4-140 2.3L SOHCSECTION Ignition Diagnostic Monitor (IDM)
Ignition Diagnostic Monitor Schematic:
The Ignition Diagnostic Monitor (IDM) circuit is an Electronic Control Assembly (ECA) input from the negative terminal of the ignition coil. The input is a comparison reference, enabling the ECA to determine if the ignition primary circuit has an intermittent fault. When the ECA gets a Profile Ignition Pickup (PIP) signal and sends a Spark Output (SPOUT) signal to the ignition module the signal should be observed by the IDM terminal at the ECA (term. 4 DG/Y wire No. 11). Failure to monitor an ignition coil signal will result in the ECA setting an intermittent failure code into memory. This allows for more diagnostic leverage when attempting to service the vehicle.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.