misfire detection ??

Misfire is detected by analyzing crankshaft speed fluctuations. The crank sensor detects engine speed, and an rpm value is established for each cylinder for comparison. When a sufficient difference in rpm occurs among cylinders, a misfire count is recorded. The rpm varies slightly because of different input variables.

Two types of misfires can be detected. A two-trip misfire, which occurs about 2% of the time, will result in an emissions increase. A one-trip misfire, also called a catalyst-damaging misfire, occurs in about 10% to 20% of the events.

To detect a misfire, the PCM must first learn the spacing of the crank target windows. This is done when the engine is in the Deceleration Fuel Shutoff mode. To learn the crank target spacing, three closed-throttle decelerations from 55 mph to rest must be performed. The misfire monitor will not be enabled until this spacing is learned.

The PCM also checks the machining tolerances within each group of slots on the flywheel. The PCM calculates the variation among each group of slots. This calculation is called rpm error. The variation in rpm readings between cylinder pairs must be less than 5% in order to run the misfire monitor.

Once the PCM has detected a misfire for two consecutive trips, the MIL will be continuously illuminated and a permanent DTC will store. If the PCM detects a catalyst-damaging misfire, the MIL will flash. If the active misfire ends, the MIL will change to continuous illumination. The MIL will remain on for more than one trip, but will go out if the conditions that set the DTC are not found on subsequent trips.

Misfire Detection

This Site Might Help You.

RE:

misfire detection ??

There are no sensors connected to spark plugs, coils, ignition wires or injectors, so how does the pcm know when a cylinder misfires and which cylinder it is ??

I know but I want to see how sharp our mechanics are. Bet I don't get a right answer, 10 points

Um, I strongly disagree with Dog, the leak detection pump code means that there is a leak in your emissions evap system that keeps your fuel vapors contained and not airborn, the most common problem is that the owner of the car or truck did not tighten the fuel cap tight enough ( the cap should rattchet four to six times to make sure there is a proper seal). And no the leak detection pump will not cause a miss fire