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 revs. or 200 revs., Judge corresponding cylinders as NG.

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	FTP 1.5 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: Ignition Order And Crankshaft Position Speed Chart

Courtesy of SUBARU OF AMERICA, INC.

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

Courtesy of SUBARU OF AMERICA, INC.

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

Courtesy of SUBARU OF AMERICA, INC.

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

Courtesy of SUBARU OF AMERICA, INC.

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

JUDGMENT VALUE (JUDGE THAT MALFUNCTION OCCURS WHEN MISFIRE RATIO IS HIGH IN 1000 ENGINE REVS.)

Malfunction Criteria	Threshold Value
FTP emission judgment value	≥ 30 x 100/2000% in 1000 revs.

Time Needed for Diagnosis: 1000 engine revs.

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

Normality Judgment

JUDGMENT VALUE CHART

Malfunction Criteria	Threshold Value
FTP emission judgment value	< 30 x 100/2000% in 1000 revs.

Time Needed for Diagnosis: 1000 engine revs.

Catalyst damage misfire (Misfire occurrence level damaging catalyst)
Abnormality Judgment

JUDGMENT VALUE CHART

Malfunction Criteria	Threshold Value
Catalyst damage misfire judgment value	≥ Value of Map 3

MAP 3 REFERENCE CHART

		Intake air (g(oz)/rev)
		0.2 (0.01)	0.4 (0.01)	0.6 (0.02)	0.8 (0.03)	1 (0.04)	1.2 (0.04)	1.4 (0.05)	1.6 (0.06)	1.8 (0.06)	2 (0.07)
Engine speed (RPM)	700	126	109	99	90	85	77	77	77	77	77
	1000	126	109	97	88	78	72	72	72	72	72
	1500	119	100	87	77	72	72	72	61	61	61
	2000	109	77	77	62	49	37	34	31	27	20
	2500	99	74	48	38	33	31	29	27	26	20
	3000	92	74	49	33	31	31	27	26	24	20
	3500	83	63	37	23	20	20	20	20	20	20
	4000	59	52	34	23	20	20	20	20	20	20
	4500	51	47	29	21	20	20	20	20	20	20
	5000	47	47	29	20	20	20	20	20	20	20
	5500	46	46	28	20	20	20	20	20	20	20
	6000	44	44	27	20	20	20	20	20	20	20
	6500	43	43	26	20	20	20	20	20	20	20
	6700	43	43	26	20	20	20	20	20	20	20

Time Needed for Diagnosis: 200 engine revs.

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

Normality Judgment

JUDGMENT VALUE CHART

Malfunction Criteria	Threshold Value
Catalyst damage misfire judgment value	< Value of Map 3

Time Needed for Diagnosis: 200 engine revs.