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 Degree Interval Difference Method 360 Degree Interval Difference Method 720 Degree Interval Difference Method	FTP 1.5 times misfire NG judgment 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.

Fig 1: Identifying Crankshaft Position Speed And Ignition Order

Courtesy of SUBARU OF AMERICA, INC.

180° 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)

Fig 2: 180° Interval Difference Method

Courtesy of SUBARU OF AMERICA, INC.

360° INTERVAL DIFFERENCE METHOD

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

Fig 3: 360° Interval Difference Method

Courtesy of SUBARU OF AMERICA, INC.

720° INTERVAL DIFFERENCE METHOD

Diagnostic value	720 degree interval difference = (A - B) - (E - F)
Misfire judgment 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)

Fig 4: 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	Threshold Value
FTP emission diagnostic value	≥ 22 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.

CATALYST-DAMAGING MISFIRE (MISFIRE OCCURRENCE LEVEL THAT WILL DAMAGE CATALYST)

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria	Threshold Value
Catalyst-damaging misfire diagnostic value	≥ Value from Map

MAP SPECIFICATION

Percentage (%)		Charging efficiency (%)
Percentage (%)		15	30	45	60	75	90	105	120	135	150	165	180
Engine speed (RPM)	700	25	25	-	-	-	-	-	-	-	-	-	-
	1000	25	25	25	25	25	25	-	-	-	-	-	-
	1500	25	25	25	25	16.75	16.75	16.75	-	-	-	-	-
	2000	25	25	25	25	16.75	14.25	12.5	-	-	-	-	-
	2500	25	25	19.75	17	14.25	12.5	11	11	-	-	-	-
	3000	25	25	19.75	17	14.25	12	10.5	10	7.75	6	-	-
	3500	25	25	19.75	17	14.25	11	9	7.75	6	5	5	5
	4000	-	25	19.75	17	14.25	11	8.25	6.25	5	5	5	5
	4500	-	25	17.5	14.25	12.5	9	6.75	5	5	5	5	5
	5000	-	25	16.75	12.5	11	8.25	6	5	5	5	5	5
	5500	-	25	16	12	11	7.25	5	5	5	5	5	5
	6000	-	25	15	11	11	6	5	5	5	5	5	5

Time needed for diagnosis: 200 engine revs.

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