Case IH 3637 – Engine Control Unit (ECU): Fuel in Oil not expected reaction (FMI 3)

The ECU infers fuel dilution by monitoring the crankcase pressure sensor. If the crankcase differential pressure sensor reads abnormally high (typically greater than 5 kPa / 0.7 psi after startup), the ECU interprets this as fuel diluting the oil. Code 3637 indicates that the ECU has detected an unexpected reaction or plausibility error regarding this fuel-in-oil calculation.

• Magnum
• Steiger
• Puma
• Maxxum
• Axial-Flow 6140
• Axial-Flow 7140
• Axial-Flow 8240
• Axial-Flow 9240

1. 1

   Check the engine oil level: Pull the dipstick to see if the oil is overfull, thin, or smells strongly of diesel, which confirms fuel dilution.

2. 2

   Inspect the blow-by filter (crankcase breather): A clogged filter will cause high crankcase pressure, tricking the ECU into detecting fuel in the oil even if the oil is fine.

3. 3

   Test the crankcase pressure sensor: Inspect the sensor and its wiring harness for damage, shorts, or open circuits that could send false high-pressure readings to the ECU.

4. 4

   Perform a fuel system leak test: If fuel dilution is confirmed, check for leaking fuel injectors, high-pressure fuel pump (CP3) shaft seal failure, or a low-pressure fuel supply pump leaking internally into the crankcase.

1. 1

   Verify Oil Condition

   Drain a small amount of engine oil. If it is NOT contaminated with fuel and the level is normal, replace the crankcase blow-by filter and test the crankcase pressure sensor.

2. 2

   Pressure Test the Fuel System

   If the oil IS contaminated, perform a fuel system pressure test to locate the internal leak (injectors, CP3 pump, or lift pump).

3. 3

   Replace the Leaking Component

   Remove and replace the faulty fuel system component causing the leak into the crankcase.

4. 4

   Change Oil and Filter

   Completely drain the contaminated engine oil and replace the engine oil filter. Refill with the OEM-specified engine oil (e.g., 15W-40).

5. 5

   Clear Codes

   Use the Electronic Service Tool (EST) to clear the fault codes from the ECU and reset the system. Run the engine and verify that crankcase pressure returns to normal parameters.