Oil dilution diagnostic test

1. A method for an engine, comprising:

responsive to detection of rich engine operation;

sealing a crankcase and spinning an engine unfueled to heat an engine lubricant; and

collecting pressure measurements at the crankcase and comparing the pressure measurements to a baseline to diagnose a presence of fuel in the engine lubricant.

2. The method of claim 1 , further comprising indicating a fuel leakage at one or more fuel injectors of the engine upon confirming the presence of the fuel in the engine lubricant and wherein indicating the fuel leakage includes setting a diagnostic trouble code (DTC) for the fuel leakage.

3. The method of claim 2 , wherein indicating the fuel leakage further includes activating an alert for an oil change.

4. The method of claim 1 , wherein spinning the engine unfueled includes spinning the engine after the engine cools to at least a threshold temperature and wherein the threshold temperature is a temperature at which the engine lubricant is not vaporized.

5. The method of claim 1 , wherein sealing the crankcase includes closing valves of a positive crankcase ventilation (PCV) system, the valves including a first valve arranged upstream of the crankcase, at an intersection of an air induction system (AIS) of the engine and a PCV vent tube, and a second valve arranged downstream of the crankcase between the crankcase and an intake manifold.

6. The method of claim 5 , wherein spinning the engine unfueled includes commanding the first valve to close and forcing the second valve to close by venting vacuum at the intake manifold.

7. The method of claim 5 , wherein collecting the pressure measurements at the crankcase includes measuring a pressure detected by a crankcase pressure (CKCP) sensor positioned in the PCV vent tube, downstream of the first valve.

8. The method of claim 1 , wherein comparing the pressure measurements to the baseline includes retrieving a baseline set of pressure measurements stored in a memory of a controller and wherein the baseline set of pressure measurements are obtained within a threshold mileage and/or period of time after an oil change.

9. The method of claim 8 , wherein obtaining the baseline set of pressure measurements includes collecting pressure data while spinning the engine unfueled with the crankcase sealed.

10. The method of claim 8 , wherein diagnosing the presence of the fuel in the engine lubricant includes determining if a pressure in the crankcase rises a threshold amount above the baseline set of pressure measurements.

11. A method for diagnosing oil dilution in a vehicle, comprising:

during a first condition, including the vehicle being in an engine-off mode and operating within a threshold mileage or duration of time subsequent to an oil change;

spinning an engine unfueled and collecting a first set of pressure measurements at a sealed crankcase; and

during a second condition, including detection of rich engine operation and the vehicle being in the engine-off mode;

spinning the engine unfueled and collecting a second set of pressure measurements at the sealed crankcase;

comparing the second set of pressure measurements to the first set of pressure measurements to identify an oil dilution by fuel in the engine; and

indicating the oil dilution by setting a diagnostic trouble code (DTC) and activating an oil change alert.

12. The method of claim 11 , wherein collecting the first set of pressure measurements at the sealed crankcase includes sealing the crankcase via a positive crankcase ventilation (PCV) system and wherein the PCV system includes a PCV vent tube extending between an air induction system (AIS) and an inlet of the crankcase and a first, PCV valve positioned between the crankcase and an intake manifold of the engine.

13. The method of claim 12 , wherein sealing the crankcase includes closing the PCV valve and closing a second valve positioned upstream of the crankcase at an intersection of the AIS and the PCV vent tube.

14. The method of claim 13 , wherein closing the PCV valve includes at least one of opening an electronic throttle to remove vacuum from the intake manifold and opening an intake valve to add compression air to the intake manifold when the PCV valve is passive.

15. The method of claim 13 , wherein closing PCV valve includes commanding the PCV valve to close when the PCV valve is electronic.

16. The method of claim 11 , further comprising stopping the collecting of the second set of pressure measurements when a pressure in the crankcase passes a threshold pressure within a pre-set duration of time or when the pre-set duration of time elapses.

17. The method of claim 11 , wherein collecting the first set of pressure measurements and collecting the second set of pressure measurements includes measuring a pressure in the crankcase by a crankcase pressure (CKCP) sensor.

18. An engine system for a vehicle, comprising:

an engine lubricated by oil and configured with a positive crankcase ventilation (PCV) system; and

a controller configured with executable instructions stored in non-transitory memory to conduct an oil dilution diagnostic test that, when executed, causes the controller to:

upon detection of rich engine operation and confirmation of an engine-off mode of the vehicle,

seal a crankcase of the engine;

spin the engine unfueled;

collect pressure measurements at the crankcase;

compare the pressure measurements to a baseline to determine a presence of fuel in the oil; and

indicate the presence of fuel in the oil by setting a diagnostic trouble code (DTC) and activating an oil change alert.

19. The engine system of claim 18 , further comprising executable instructions to repeat the oil dilution diagnostic test based on an increment of vehicle mileage to confirm an increase in an amount of oil dilution.

20. The engine system of claim 18 , wherein comparison of the pressure measurements to the baseline includes normalization of the pressure measurements to an oil temperature.