When the misfire detection monitor detects a misfire, the check engine light will flash as the misfire is occurring. But the light will not remain on the first time a misfire problem is detected. It will come on only if the misfire continues during a second drive cycle and will set a P series code. A P code would indicate a random misfire probably due to a vacuum leak, open EGR valve, etc. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring.
Create a free Team What is Teams? Learn more. How does the car's ECU detect a misfire? Ask Question. Asked 5 years, 7 months ago. Active 2 years, 4 months ago. Viewed 19k times. Improve this question. Robert S. Barnes Robert S. Barnes Add a comment. Active Oldest Votes. Improve this answer. Summing up: you can detect misfire by looking at spark plug voltage.
HandyHowie Autistic Autistic 2, 1 1 gold badge 14 14 silver badges 27 27 bronze badges. Interesting, although it doesn't look like this is very common on vehicles, it seems like more of a tailpipe emissions testing technology. Figure 1 — Instantaneous engine speeds vs crank angle for normal combustion and misfire.
The OpenECU Simulink blockset provides an easy way to calculate the engine speed during specific portions of the engine cycle using the crankshaft position sensor. In the example shown in Figure 2, each instance of the Engine Speed block is used to calculate the average engine speed over a different portion of the engine cycle. The first block gives the average engine speed over degrees of crank rotation.
The tooth range is calibratable, which means that it can be easily adjusted in real-time to account for varying operating conditions, such as a change in the spark timing, which can affect the location of the fastest crank speed relative to the TDC of the cylinder. The tooth ranges can be specified relative to the TDC of each cylinder, or relative to the missing tooth region of the crankshaft position sensor pickup wheel.
Each cylinder will have its own pair of blocks to detect the maximum and minimum crank speeds. The speeds calculated by the OpenECU blocks can then be compared and a misfire event can be detected if the separation between the two indicates that the crankshaft did not accelerate during the power stroke. The figure below shows the pre and post TDC engine speeds when misfire events are induced on a single cylinder engine using an ignition cut.
The reduced difference between the pre and post TDC engine speeds clearly shows the misfire events. Figure 1 — Instantaneous engine speeds vs crank angle for normal combustion and misfire The OpenECU Simulink blockset provides an easy way to calculate the engine speed during specific portions of the engine cycle using the crankshaft position sensor. Figure 2 — Example implementation of TDC relative engine speed measurement with OpenECU The figure below shows the pre and post TDC engine speeds when misfire events are induced on a single cylinder engine using an ignition cut.
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