Diagnostic Method

WARNING: This page is about a different variant/trim than selected.

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	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: Crankshaft Position Speed And Ignition Order Chart

Courtesy of SUBARU OF AMERICA, INC.

180° Interval Difference Method

Diagnostic value	180 degree interval difference = {(C - B) - (G - C)/4} - {(B - A) - (F - B)/4}
Misfire judgment 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: Crankshaft Position Speed Graph - 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: Crankshaft Position Speed Graph - 360° Interval Difference Method

Courtesy of SUBARU OF AMERICA, INC.

720° Interval Difference Method

Diagnostic value	720 degree interval difference = (B - A) - (F - E)
Misfire judgment	720 degree interval difference > Judgment value → Judged as misfire

Fig 4: Crankshaft Position Speed Graph - 720° Interval Difference Method

Courtesy of SUBARU OF AMERICA, INC.

FTP 1.5 times misfire (misfire occurrence level which influences exhaust gas)

Time needed for diagnosis: 1000 engine revs.

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

Judgment value (Judge that malfunction occurs when the misfire ratio is high in 1000 engine revs.)

Malfunction Criteria	Threshold Value
FTP emission diagnostic value (Except for PZEV model)	≥ 45 x 100/2000% in 1000 revs. (CVT model) ≥ 64 x 100/2000% in 1000 revs. (MT model)
FTP emission diagnostic value (PZEV model)	≥ 48 x 100/2000% in 1000 revs.

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 2

Map 2

		Amount of intake air g/rev (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
	1000	100	100	100	80	80	80	52	24
	1500	100	100	80	80	80	57	36	26
	2000	80	80	80	80	80	44	26	26
	2500	68	68	68	58	58	35	26	26
	3000	57	57	57	36	36	26	26	26
	3500	55	46	42	30	28	20	20	20
	4000	55	36	26	20	20	20	20	20
	4500	50	28	20	20	20	20	20	20
	5000	50	20	20	20	20	20	20	20
	5500	40	20	20	20	20	20	20	20
	6000	40	20	20	20	20	20	20	20
	6400	40	20	20	20	20	20	20	20
g/rev

Time needed for diagnosis: 200 engine revs.

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