Diagnostic Method: Notes

When a misfire occurs, the engine speed will decreased and the crankshaft position speed will change. Calculate the interval difference value (diagnostic value) from crankshaft position speed by the following formula, and judge whether a misfire is occurring or not comparing the calculated result with judgment value. Counting the number of misfires. If the misfire ratio is higher during 1000 revs, or 200 revs. Judge corresponding cylinders as NG.

Fig 1: [Interval Difference Value Calculation Formula]

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As shown in the following figure, pick a cylinder as the standard and name it omg 0. And the former crankshaft position speed is named omg 1, the second former crankshaft position speed is named omg 2, the third is named omg 3, etc.

Fig 2: Identifying Ignition Order And Crankshaft Position Speed

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180° Interval Difference Method

DIAGNOSTIC VALUE - 180° INTERVAL DIFFERENCE METHOD

Diagnostic value	domg 180 = (omg 1 - omg 0) - (omg 5 - omg 1)/ 4
Judge as a misfire in the following cases. domg 180 > judgment value of positive side domg 180 ≤ judgment value of negative side (Judgment value before 180° CA)

Fig 3: Threshold Value Graph For 180° Interval Difference Method

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360° Interval Difference Method

DIAGNOSTIC VALUE - 360° INTERVAL DIFFERENCE METHOD

Diagnostic value	domg 360 = (omg 1 - omg 0) - (omg 3 - omg 2)
Misfire judgment	domg 360 > Judgment value → Judge as misfire

Fig 4: Threshold Value Graph For 360° Interval Difference Method

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720° Interval Difference Method

DIAGNOSTIC VALUE - 720° INTERVAL DIFFERENCE METHOD

Diagnostic value	domg 720 = (omg 1 - omg 0) - (omg 5 - omg 4)
Misfire judgment	domg 720 > Judgment value → Judge as misfire

Fig 5: Threshold Value Graph For 720° Interval Difference Method

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FTP 1.5 times misfire (Misfire occurrence level which influences exhaust gas)

Judgment Value (Judge that malfunction occurs when the misfire ratio is high in 1000 engine revs.)

MALFUNCTION CRITERIA AND THRESHOLD VALUE REFERENCE

Malfunction Criteria	Threshold Value
FTP emission judgment value	> 1.0% in 1000 revs.

Time Needed for Diagnosis: 1000 engine revs.

Malfunction Indicator Light Illumination: Illuminates when malfunction occurs in 2 continuous driving cycles.

Catalyst damage misfire (Misfire occurrence level damaging catalyst)

Judgment Value (Judge that malfunction occurs when the misfire ratio is high in 200 engine revs. (400 ignitions))

MALFUNCTION CRITERIA AND THRESHOLD VALUE REFERENCE

Malfunction Criteria	Threshold Value
Catalyst damage misfire judgment value	See

Map 1 Fault criteria threshold for misfire which would result in catalyst damage