Diagnostic Method

WARNING: This page is about a different car, the 2013 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.

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	≥ 17 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

Malfunction Criteria	Threshold Value
FTP emission diagnostic value	< 17 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

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

MAP 3

		Intake air (g(oz)/rev)
		0.2 (0.01)	0.4 (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	100	100	100	100	100	90	90	90	90	90
	1000	100	100	100	100	92	85	85	85	85	85
	1500	100	100	100	90	85	85	85	72	72	72
	2000	100	90	90	73	58	43	40	36	32	20
	2500	100	87	57	45	39	36	34	32	30	20
	3000	100	87	58	39	36	36	32	30	28	20
	3500	98	74	43	27	23	22	20	20	20	20
	4000	69	61	40	27	22	20	20	20	20	20
	4500	60	55	34	25	20	20	20	20	20	20
	5000	55	55	34	23	20	20	20	20	20	20
	5500	54	54	33	22	20	20	20	20	20	20
	6000	52	52	32	21	20	20	20	20	20	20
	6500	50	50	30	20	20	20	20	20	20	20
	6700	50	50	30	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.