Diagnostic Method

When a misfire occurs, the engine speed will decrease 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. Count 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 value)
	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: Identifying Ignition Order And Crankshaft Position Speed

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 (Diagnostic value before 180° CA)

Fig 2: Misfire Judgement 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: Misfire Judgement 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: Misfire Judgement 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 diagnostic value	≥ 47 x 100/2000% in 1000 revs. (except for PZEV model) ≥ 17 x 100/2000% in 1000 revs. (PZEV AT model) ≥ 21 x 100/2000% in 1000 revs. (PZEV MT model)

Time Needed for Diagnosis: 1000 engine revs.

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

Normality Judgment

JUDGMENT VALUE

Malfunction Criteria	Threshold Value
FTP emission diagnostic value	< 47 x 100/2000% in 1000 revs. (except for PZEV model) < 17 x 100/2000% in 1000 revs. (PZEV AT model) < 21 x 100/2000% in 1000 revs. (PZEV MT model)

Time Needed for Diagnosis: 1000 engine revs.

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

JUDGMENT VALUE

Malfunction Criteria	Threshold Value
Catalyst damage misfire diagnostic value	≥ Value from Map 3

MAP 3

		Intake air (g(oz)/rev)
		0.2 (0.01)	0.3 (0.01)	0.4 (0.01)	0.5 (0.02)	0.6 (0.02)	0.8 (0.03)	0.9 (0.03)	1.1 (0.04)
Engine speed (rpm)	650	100	100	100	100	100	80	64	48
	000	100	100	100	80	80	80	52	24
	500	100	100	80	80	80	57	36	26
	000	80	80	80	80	80	44	26	26
	500	68	68	68	58	58	35	26	26
	000	57	57	57	36	36	26	26	26
	500	55	46	42	30	28	20	20	20
	000	55	36	26	20	20	20	20	20
	500	50	28	20	20	20	20	20	20
	000	50	20	20	20	20	20	20	20
	500	40	20	20	20	20	20	20	20
	000	40	20	20	20	20	20	20	20
	400	40	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

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

Time Needed for Diagnosis: 200 engine revs.