Diagnostic Method

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 rev. or 200 rev. Judge corresponding cylinders as NG.

INTERVAL DIFFERENCE VALUE CALCULATION FORMULA

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)
	120 degree difference method 360 degree difference method 720 degree 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.

120° Interval Difference Method

DIAGNOSTIC VALUE - 120° INTERVAL DIFFERENCE METHOD

Diagnostic value	domg 120 = (omg 1 - omg 0) - (omg 7 - omg 1)/6
Judge as a misfire in the following cases. domg 120 > judgment value of positive side domg 121 ≤ judgment value of negative side (Judgment value before 120°CA)

Fig 2: Diagnostic Value For 120° Interval Difference Method

Courtesy of SUBARU OF AMERICA, INC.

360° Interval Difference Method

DIAGNOSTIC VALUE - 360° INTERVAL DIFFERENCE METHOD

Diagnostic value	domg 360 = (omg 1 - omg 0) - (omg 4 - omg 3)
Misfire judgment	domg 360 > Judgment value → Judge as misfire

Fig 3: Diagnostic Value For 360° Interval Difference Method

Courtesy of SUBARU OF AMERICA, INC.

720° Interval Difference Method

DIAGNOSTIC VALUE - 720° INTERVAL DIFFERENCE METHOD

Diagnostic value	domg 720 = (omg 1 - omg 0) - (omg 7 - omg 6)
Misfire judgment	domg 720 > Judgment value → Judge as misfire

Fig 4: Diagnostic Value For 720° Interval Difference Method

Courtesy of SUBARU OF AMERICA, INC.

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% at 1000 revs.

Time Needed for Diagnosis: 1000 revs.

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

Catalyst damage misfire (Misfire occurrence level to damage catalyst)

Judgment Value

MALFUNCTION CRITERIA AND THRESHOLD VALUE REFERENCE

Malfunction Criteria	Threshold Value
Catalyst damage misfire judgment value	Refer to Map.

Map

INTAKE AIR AMOUNT SPECIFICATION

		Intake air (g (oz)/rev)
		0.2 (0.035)	0.4 (0.014)	0.6 (0.021)	0.8 (0.028)	1 (0.035)	1.2 (0.042)	1.4 (0.049)	1.6 (0.056)	1.8 (0.063)	2 (0.071)
engine speed (rpm)	700	90	90	88	76	68	78	78	78	78	78
	1000	90	90	88	76	68	78	78	78	78	78
	1500	89	88	80	64	56	62	62	62	62	62
	2000	88	84	64	40	36	35	35	35	35	35
	2500	88	80	56	36	24	34	34	34	34	34
	3000	64	56	26	23	23	33	33	33	33	33
	3500	50	40	24	24	32	32	32	32	32	32
	4000	40	38	30	26	20	20	20	20	20	20
	4500	50	28	20	20	20	20	20	20	20	20
	5000	40	30	20	20	20	20	20	20	20	20
	5500	40	25	26	21	20	20	20	20	20	20
	6000	36	36	25	20	20	20	20	20	20	20
	6500	32	32	20	20	20	20	20	20	20	20
	7000	32	32	20	20	20	20	20	20	20	20

Time Needed for Diagnosis: 200 revs.

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