Diagnostic Method

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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 rpm or 2000 rpm, judge corresponding cylinders as NG.

DIAGNOSTIC METHOD

Diagnostic value calculation (Calculate from angle speed) →	Misfire detection every single ignition (Compare diagnostic value with judgment value) →	NG judgment (Misfire occurrence judgment required by the law) (Compare number of misfire with judgment)
	180° Interval Difference Method 360° Interval Difference Method 720° Interval Difference Method	FTP1.5 times misfire NG judgment Catalyst damage misfire NG judgment

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 1: Crankshaft Position Speed Chart

180° Interval Difference Method

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 2: Crankshaft Position Speed Graph - 180° Interval Difference Method

360° Interval Difference Method

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 3: Crankshaft Position Speed Graph - 360° Interval Difference Method

720° Interval Difference Method

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 4: Crankshaft Position Speed Graph - 720° Interval Difference Method

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.)

JUDGMENT VALUE CHART

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))

JUDGMENT VALUE CHART

Malfunction Criteria	Threshold Value
Catalyst damage misfire judgment value	See ENGINE SPEED SPECIFICATION CHART

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

ENGINE SPEED SPECIFICATION CHART

percentage		Intake air (g(oz)/rev)
percentage		0.16 (0.0006)	0.28 (0.010)	0.4 (0.014)	0.52 (0.018)	0.64 (0.023)	0.76 (0.027)	0.92 (0.032)	1.1 (0.039)	1.2 (0.042)	1.3 (0.046)
Engine speed (rpm)	700	25	25	25	25	22.5	20	16	12	12	12
	1000	25	25	25	25	22.5	20	15.75	11	11	11
	1500	25	25	22.5	20	18.25	16.75	13.5	10	10	10
	2000	20	20	20	20	17	14.25	12.75	11	11	11
	2500	20	20	18.25	16.75	15.5	14.25	12.75	11	11	11
	3000	16.75	16.75	15.5	14.25	12.75	11	11	11	11	11
	3500	16.75	16.75	14	11	10	9	8.5	7.75	7.75	7.75
	4000	14.25	14.25	11	7.75	6	5	5	5	5	5
	4500	11	11	8.25	7.75	5	5	5	5	5	5
	5000	11	11	9.5	7.75	5	5	5	5	5	5
	5500	9	9	7.75	6.75	5	5	5	5	5	5
	6000	9	5	5	5	5	5	5	5	5	5
	6400	9	5	5	5	5	5	5	5	5	5

These figures indicate the misfire rate (%) in 400 ignitions; for example, 22.5 (%) means 400 (ignition) x 22.5 (%) = 90 (ignition) misfires. This value or more is judged as a misfire.

Time Needed for Diagnosis: 200 engine revs.

Malfunction Indicator Light Illumination: Illuminates as soon as a malfunction occurs.