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 in 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 Degree Interval Difference Method 360 Degree Interval Difference Method 720 Degree Interval Difference Method	NG judgment for exhaust gas misfire NG judgment for catalyst-damaging misfire

As shown in the following figure, pick a cylinder as the standard and name it A. And the former crankshaft position speed is named B, the second former crankshaft position speed is named C, the third is named D..., etc.

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC VALUE SPECIFICATION (180 DEGREE INTERVAL DIFFERENCE METHOD)

Diagnostic value	180 degree interval difference = (A - B) - (B - C)
Judge as a misfire in the following cases. 180 degree interval difference>Judgment value of positive side 180 degree interval difference < Judgment value of negative side (Diagnostic value before 180°CA)

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC VALUE SPECIFICATION (360 DEGREE INTERVAL DIFFERENCE METHOD)

Diagnostic value	360 degree interval difference = (B - A) - (D - C)
Misfire judgment	360 degree interval difference>Judgment value → Judged as misfire

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC VALUE SPECIFICATION (720 DEGREE INTERVAL DIFFERENCE METHOD)

Diagnostic value	720 degree interval difference = (A - B) - (E - F)
Judge as a misfire in the following cases. 720 degree interval difference ≥ Judgment value of positive side 720 degree interval difference ≤ Judgment value of negative side (Diagnostic value before 720°CA)

Courtesy of SUBARU OF AMERICA, INC.

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

Malfunction Criteria	Threshold Value
Diagnostic value of exhaust gas misfire	25 x 100/2000 % or more in 1000 revs.

Time needed for diagnosis: 1000 engine revs.

Malfunction indicator light illumination: Illuminates when malfunction occurs in 2 continuous driving cycles.

CATALYST-DAMAGING MISFIRE (MISFIRE OCCURRENCE LEVEL THAT WILL DAMAGE CATALYST) JUDGMENT VALUE SPECIFICATION

Malfunction Criteria	Threshold Value
Catalyst-damaging misfire diagnostic value	Value of Map or more

PERCENTAGE SPECIFICATION - MAP

Percentage (%)		Charging efficiency (%)
Percentage (%)		15	30	45	60	75	90	105	120	135	150	165	180
Engine speed (rpm)	700	20	20	20	20	20	20	20	20	20	20	20	20
	1000	20	20	20	20	20	20	20	20	20	20	20	20
	1500	20	20	20	20	16.5	16.5	14.25	14.25	12.5	12.5	12.5	12.5
	2000	20	20	20	20	16.5	14.25	11	10	9	9	9	9
	2500	20	20	20	16.5	14.25	12.5	10	9	9	9	9	9
	3000	20	20	20	16.5	12.5	11	9	8.25	9	9	9	9
	3500	20	16.5	16.5	12.5	10	9	8.25	8.25	8.25	8.25	8.25	8.25
	4000	20	16.5	16.5	11	7.5	7.5	7.5	7.5	7.5	7.5	7.5	7.5
	4500	20	16.5	14.25	11	7.5	7.5	7.5	7.5	7.5	7.5	7.5	7.5
	5000	20	16.5	12.5	10	7.5	7.5	7.5	7.5	7.5	7.5	7.5	7.5
	5500	20	16.5	12.5	10	7.5	7.5	7.5	7.5	7.5	7.5	7.5	7.5
	6000	20	16.5	12.5	10	7.5	7.5	7.5	7.5	7.5	7.5	7.5	7.5
	6100	20	16.5	12.5	10	7.5	7.5	7.5	7.5	7.5	7.5	7.5	7.5

Time needed for diagnosis: 200 engine revs.

Malfunction indicator light illumination: Illuminates as soon as a malfunction occurs.