Systems for diagnosing a condition of an engine

1. A system comprising:

a crankcase pressure sensor configured to measure crankcase pressure of an engine having a plurality of cylinders; and

a controller configured to:

sample a signal output from the crankcase pressure sensor;

process the sampled signal to determine a half-order magnitude of a half-order frequency component of the sampled signal;

diagnose a condition of the engine based on a change in the half-order magnitude of the half-order frequency component, including diagnosing a degraded component of a positive crankcase ventilation (PCV) system when the change in the half-order magnitude is greater than a threshold change;

adjust one or more engine operating parameters responsive to the diagnosing; and

wherein the controller is configured to adjust one or more engine operating parameters by adjusting a fuel injection amount or timing.

2. The system of claim 1 , further comprising

a crankshaft speed sensor,

wherein the controller is configured to sample a speed signal output by the crankshaft speed sensor and process the sampled speed signal to determine the half-order magnitude of the half-order frequency component of the sampled speed signal; and

the controller is configured to diagnose cylinder knock when the half-order magnitude of the sampled speed signal is greater than a threshold magnitude.

3. The system of claim 1 ,

wherein the controller is configured to sample the signal from the crankcase pressure sensor at a timing corresponding to sample timing of a crankshaft speed sensor; and

wherein the controller is configured to diagnose cylinder knock when the half-order magnitude of the half-order frequency component of the sampled signal from the crankcase pressure sensor is greater than a threshold magnitude.

4. The system of claim 1 , wherein the change in the half-order magnitude includes a difference between a first half-order magnitude when the PCV system is active and a second half-order magnitude when the PCV system is inactive, and wherein the component of the PCV system comprises an oil filter.

5. The system of claim 4 , wherein the controller is configured to:

when the change in the half-order magnitude is not greater than the threshold change and the first half-order magnitude is greater than a threshold magnitude, diagnose degradation of a cylinder component.

6. The system of claim 1 ,

further comprising an exhaust NOx sensor;

wherein the controller is configured to sample a NOx signal output from the exhaust NOx sensor during low engine speed conditions where each cylinder is sequentially over-fueled and process the sampled NOx signal to determine a half-order magnitude of a half-order frequency component of the sampled NOx signal; and

wherein the controller is configured to diagnose cylinder misfire when the half-order magnitude of the sampled NOx signal is greater than a threshold magnitude.

7. The system of claim 1 ,

further comprising an exhaust pressure sensor or an exhaust temperature sensor;

wherein the controller is configured to sample a second signal output by the exhaust pressure sensor or exhaust temperature signal and process the sampled second signal to determine a half-order magnitude of a half-order frequency component of the sampled second signal; and

wherein the controller is configured to diagnose cylinder misfire when the half-order magnitude of the sampled second signal is greater than a threshold magnitude.

8. A system comprising:

an engine having a plurality of cylinders coupled to a crankshaft;

a crankshaft speed sensor; and

a controller configured to:

sample output from the crankshaft speed sensor;

process the sampled output to obtain a plurality of magnitudes each corresponding to a respective frequency component;

sum each of the plurality of magnitudes to generate a combined magnitude;

indicate cylinder knock in one cylinder based on a selected frequency component of the sampled output from the crankshaft speed sensor, including indicating cylinder knock when the combined magnitude is greater than a threshold magnitude;

responsive to indicating cylinder knock in the one cylinder, identify which cylinder is knocking based on a phase of a selected frequency component signal of the output from the crankshaft speed sensor; and

adjust a fuel injection amount to the knocking cylinder.

9. The system of claim 8 , wherein the controller is configured to detect the cylinder knock based on the output from the crankshaft speed sensor independent of output from a knock sensor.

10. The system of claim 8 , wherein the controller is configured to:

process the sampled output to obtain a half order frequency component of the sampled output from the crankshaft speed sensor;

determine a magnitude of the half order frequency component; and

indicate cylinder knock in the one cylinder of the engine if the magnitude is greater than a threshold magnitude.

11. The system of claim 8 , wherein the controller is configured to:

process the sampled output to obtain a sixth order frequency component of the sampled output from the crankshaft speed sensor;

determine a magnitude of the sixth order frequency signal; and

indicate cylinder knock in each cylinder of the engine if the magnitude is greater than a threshold magnitude.

12. A system comprising:

an engine having a plurality of cylinders coupled to a crankshaft;

a crankshaft speed sensor; and

a controller configured to:

sample a signal output from the crankshaft speed sensor;

process the sampled signal to determine a plurality of magnitudes each corresponding to a respective frequency component of the signal, the plurality of magnitudes determined from the signal sampled during a given range of piston positions for a cylinder of the engine;

sum each of the plurality of magnitudes to generate a combined magnitude;

detect cylinder knock of the cylinder when the combined magnitude exceeds a threshold magnitude;

adjust one or more engine operating parameters responsive to the detection of cylinder knock; and

wherein the controller is configured to adjust one or more engine operating parameters by adjusting a fuel injection amount to a knocking cylinder.

13. The system of claim 12 , wherein the given range of piston positions comprises ten to seventy degrees after top dead center.

14. The system of claim 2 , wherein the controller is configured to process the sampled speed signal to obtain a plurality of additional magnitudes each corresponding to a respective additional frequency component of the sampled speed signal, sum each of the plurality of additional magnitudes and the half-order magnitude of the sampled speed signal to generate a combined magnitude, and indicate cylinder knock when the combined magnitude is greater than the threshold magnitude.