Systems and methods for diagnosing valve lift mechanisms and oil control valves of camshaft lift systems

1. A system for an engine comprising:

a signal monitoring module that receives a cylinder fuel correction signal when an engine speed signal is within a first predetermined range of a speed for a predetermined period and an engine load signal is within a second predetermined range of a load for the predetermined period; and

a fault detection module that detects a fault of at least one of a switchable roller finger follower (SRFF) and an oil control valve (OCV) based on the cylinder fuel correction signal and an exhaust gas recirculation (EGR) value,

wherein the cylinder fuel correction signal is generated based on: an engine position signal; and at least one of an oxygen signal and a wide range air fuel (WRAF) signal.

2. The system of claim 1 , further comprising a valve overlap control module that controls activation of intake and exhaust camshafts of a camshaft lift system to adjust an overlap between intake and exhaust strokes for each of N cylinders, where N is an integer greater than 1,

wherein the valve overlap control module determines the EGR value based on the overlap,

wherein the valve overlap control module adjusts camshaft phasing of intake and exhaust valves based on the EGR value, and

wherein the valve overlap control module maintains a predetermined level of residual exhaust gas for each of the N cylinders by setting the camshaft phasing of the intake and exhaust valves to a predetermined position.

3. The system of claim 1 , wherein the signal monitoring module samples the cylinder fuel correction signal during a diagnostic event,

wherein the signal monitoring module stores sampled fuel correction values of the cylinder fuel correction signal as first values when a camshaft lift system is operating in a first lift state, and

wherein the signal monitoring module stores the sampled fuel correction values as second values when the camshaft lift system is operating in a second lift state.

4. The system of claim 3 , further comprising a camshaft transition module that intrusively commands the camshaft lift system to transition from the first lift state to the second lift state after the signal monitoring module stores the first values during the first lift state, and

wherein the signal monitoring module stores the second values during the second lift state.

5. The system of claim 3 , further comprising a signal comparison module that determines differences between the first values and the second values,

wherein the fault detection module generates a fault control signal that indicates the fault when at least one of the differences is greater than a first predetermined threshold, and

wherein the fault detection module generates the fault control signal when at least one of the differences is less than a second predetermined threshold.

6. The system of claim 5 , wherein the fault control signal indicates that the fault is with at least one of the SRFFs when the fault control signal is associated with Y of X cylinders, where X is a number of cylinders that are controlled by the OCV and Y is less than X, and

wherein the fault control signal indicates that the fault is with the OCV when the fault control signal is associated with the X cylinders.

7. The system of claim 3 , wherein the fault detection module, based on a fault control signal, at least one of: limits speed of the engine to a first predetermined speed; permits a first lift state change from the first lift state to the second loft state; and prevents a second lift state change from the second lift state to the first lift state.

8. The system of claim 5 , wherein the signal monitoring module stores the sampled fuel correction values as third values when the engine speed signal is less than a second predetermined speed,

wherein the signal monitoring module stores the sampled fuel correction values as fourth values when the engine speed signal is greater than a third predetermined speed,

wherein the signal comparison module determines differences between the third values and the fourth values, and

wherein the fault detection module generates a fault control signal when at least one of the differences is greater than a third predetermined threshold.

9. The system of claim 5 , wherein the signal monitoring module stores the sampled fuel correction values as fifth values when camshaft phasing of intake and exhaust valves is set to a first predetermined position,

wherein the signal monitoring module stores the sampled fuel correction values as sixth values when the camshaft phasing of the intake and exhaust valves is set to a second predetermined position,

wherein the signal comparison module determines differences between the fifth values and the sixth values, and

wherein the fault detection module generates a fault control signal when at least one of the differences is greater than a fourth predetermined threshold.

10. The system of claim 1 , wherein the signal monitoring module receives an air/fuel ratio imbalance signal when: the engine speed signal is within the first predetermined range for the predetermined period; the engine load signal is within the second predetermined range for the predetermined period; and a carbon canister vapor signal is within a third predetermined range for the predetermined period,

wherein the fault detection module detects the fault based on the air/fuel ratio imbalance signal and the EGR value, and

wherein the air/fuel ratio imbalance signal is generated based on: the engine position signal; and at least one of the oxygen signal and the WRAF signal.

11. A system for an engine comprising:

a signal monitoring module that receives an air/fuel ratio imbalance signal when an engine speed signal is within a first predetermined range of a speed for a predetermined period and an engine load signal is within a second predetermined range of a load for the predetermined period; and

a fault detection module that detects a fault of at least one of a switchable roller finger follower (SRFF) and an oil control valve (OCV) based on the air/fuel ratio imbalance signal and at least one of a residual exhaust gas level of a cylinder of the engine and an intake-to-exhaust camshaft overlap,

wherein the air/fuel ratio imbalance signal is generated based on: an engine position signal; and at least one of an oxygen signal and a wide range air fuel (WRAF) signal.

12. The system of claim 11 , wherein the signal monitoring module samples the air/fuel ratio imbalance signal during a diagnostic event,

wherein the signal monitoring module stores sampled imbalance values of the air/fuel ratio imbalance signal as first values when a camshaft lift system is operating in a first lift state, and

wherein the signal monitoring module stores the sampled imbalance values as second values when the camshaft lift system is operating in a second lift state.

13. The system of claim 12 , further comprising a signal comparison module that determines differences between the first values and the second values,

wherein the fault detection module generates a fault control signal that indicates the fault when at least one of the differences is greater than a first predetermined threshold, and

wherein the fault detection module generates the fault control signal when at least one of the differences is less than a second predetermined threshold.

14. The system of claim 13 , wherein the signal monitoring module stores the sampled fuel correction values as third values when camshaft phasing of intake and exhaust valves is set to a first predetermined position,

wherein the signal monitoring module stores the sampled fuel correction values as fourth values when the camshaft phasing of the intake and exhaust valves is set to a second predetermined position,

wherein the signal comparison module determines differences between the third values and the fourth values, and

wherein the fault detection module generates a fault control signal when at least one of the differences is greater than a third predetermined threshold.

15. A method of diagnosing a camshaft lift system comprising:

receiving at least one of a cylinder fuel correction signal and an air/fuel ratio imbalance signal when: an engine speed signal is within a first predetermined range of a speed for a predetermined period; and an engine load signal is within a second predetermined range of a load for the predetermined period;

detecting a fault of at least one of a switchable roller finger follower (SRFF) and an oil control valve (OCV) based on an exhaust gas recirculation (EGR) value and at least one of the cylinder fuel correction signal and the air/fuel ratio imbalance signal; and

generating the cylinder fuel correction signal and the air/fuel ratio imbalance signal based on: an engine position signal; and at least one of an oxygen signal and a wide range air fuel (WRAF) signal.

16. The method of claim 15 , further comprising:

controlling activation of intake and exhaust camshafts of a camshaft lift system to adjust an overlap between intake and exhaust strokes for each of N cylinders, where N is an integer greater than 1;

determining the EGR value based on the overlap;

adjusting camshaft phasing of intake and exhaust valves based on the EGR value; and

maintaining a predetermined level of residual exhaust gas for each of the N cylinders by setting the camshaft phasing of the intake and exhaust valves to a predetermined position.

17. The method of claim 15 , further comprising:

sampling at least one of the cylinder fuel correction signal and the air/fuel ratio imbalance signal during a diagnostic event,

storing sampled values from at least one of the cylinder fuel correction signal and the air/fuel ratio imbalance signal as first values when at least one of: a camshaft lift system is operating in a first lift state; and camshaft phasing of intake and exhaust valves is set to a first predetermined position, and

wherein the sampled values are stored as second values when at least one of: the camshaft lift system is operating in a second lift state; and the camshaft phasing of the intake and exhaust valves is set to a second predetermined position.

18. The method of claim 17 , further comprising:

intrusively commanding the camshaft lift system to transition from the first lift state to the second lift state after the signal monitoring module stores the first values during the first lift state; and

storing the second values during the second lift state.

19. The method of claim 17 , further comprising:

determining differences between the first values and the second values;

generating a fault control signal that indicates the fault when at least one of the differences is greater than a first predetermined threshold; and

generating the fault control signal that indicates the fault when at least one of the differences is less than a second predetermined threshold.

20. The method of claim 19 , further comprising:

indicating that the fault is with at least one of the SRFFs when the fault control signal is associated with Y of X cylinders, where X is a number of cylinders that are controlled by the OCV and Y is less than X; and

indicating that the fault is with the OCV when the fault control signal is associated with the X cylinders.

21. The method of claim 20 , further comprising:

limiting speed of the engine to a first predetermined speed based on the fault control signal;

permitting a first lift state change from the first lift state to the second lift state based on the fault control signal; and

preventing a second lift state change from the second lift state to the first lift state based on the fault control signal.

22. The method of claim 20 , further comprising:

storing the sampled values as third values when the engine speed signal is less than a second predetermined speed;

storing the sampled values as fourth values when the engine speed signal is greater than a third predetermined speed;

determining differences between the third values and the fourth values; and

generating the fault control signal when at least one of the differences is greater than a third predetermined threshold.