Diagnostic Method

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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.

180° INTERVAL DIFFERENCE METHOD

Diagnostic value 180 degree interval difference = {(C - B) - (G - C)/4} - {(B - A) - (F - B)/4}
Judge as a misfire in the following cases. 180 degree interval difference: More than judgment value of positive side 180 degree interval difference: Judgment value of negative side or less (Diagnostic value before 180°CA)

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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

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

Courtesy of SUBARU OF AMERICA, INC.

Exhaust gas misfire (misfire occurrence level which influences exhaust gas) Judgment value (judge that malfunction occurs when the misfire ratio is high in 1000 engine revs.)

JUDGMENT VALUE SPECIFICATIONS

Malfunction Criteria	Threshold Value
Diagnostic value of exhaust gas misfire	52 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 SPECIFICATIONS

Malfunction Criteria	Threshold Value
Catalyst-damaging misfire diagnostic value	Value of Map2 or more

AMOUNT OF INTAKE AIR - 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)	0.7 (0.02)	0.8 (0.03)	0.9 (0.03)	1 (0.04)	1.1 (0.04)
Engine speed (rpm)	1000 rpm	80	80	80	80	80	80	80	66	66	66
	1200 rpm	80	80	80	80	80	80	80	66	66	66
	1600 rpm	80	80	80	80	80	66	66	57	57	57
	2000 rpm	80	80	80	80	80	66	57	44	44	44
	2400 rpm	80	80	80	80	80	57	44	36	30	30
	2800 rpm	80	80	80	80	57	44	40	33	30	30
	3200 rpm	80	80	80	80	57	44	40	30	30	30
	3600 rpm	66	66	66	57	50	40	36	30	30	30
	4000 rpm	57	57	50	50	44	36	30	28	28	28
	4400 rpm	57	57	44	40	36	30	28	28	28	28
	4800 rpm	50	50	40	36	33	30	28	26	25	25
	5200 rpm	40	40	33	30	28	28	26	25	23	23
	5600 rpm	33	33	28	26	25	25	23	22	21	21
	5900 rpm	28	28	23	23	22	22	21	21	20	20
(g/rev)

Time needed for diagnosis: 200 engine revs.

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