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)
	120 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: Ignition Order And Crankshaft Position Speed

Courtesy of SUBARU OF AMERICA, INC.

120° Interval Difference Method

Diagnostic value	120 degree interval difference = (B - A) - (H - B)/6
Misfire judgment Judge as a misfire in the following cases. 120 degree interval difference > Judgment value of positive side 120 degree interval difference ≤ Judgment value of negative side (Diagnostic value before 120° CA)

Fig 2: 120 Degree Interval Difference And Misfire Graph

Courtesy of SUBARU OF AMERICA, INC.

360° Interval Difference Method

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

Fig 3: 360 Degree Interval Difference And Misfire Graph

Courtesy of SUBARU OF AMERICA, INC.

720° Interval Difference Method

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

Fig 4: 720 Degree Interval Difference And Misfire Graph

Courtesy of SUBARU OF AMERICA, INC.

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

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria	Threshold Value
FTP emission diagnostic value	≥ 63 x 100/3000% 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 2

MAP 2 VALUE SPECIFICATION

		Amount of intake air g/rev (oz/rev.)
		0.16 (0.01)	0.28 (0.01)	0.4 (0.01)	0.52 (0.02)	0.64 (0.02)	0.76 (0.03)	0.92 (0.03)	1.1 (0.04)	1.5 (0.05)	2 (0.07)
Engine speed (rpm)	650	150	150	150	150	150	120	96	72	72	72
	1000	150	150	150	120	120	120	78	36	36	36
	1500	150	150	120	120	120	85.5	54.6	40.2	40.2	40.2
	2000	120	120	120	120	120	66.6	40.2	40.2	40.2	40.2
	2500	102.75	102.75	102.9	87.3	87.3	53.4	40.2	40.2	40.2	40.2
	3000	85.8	85.8	85.8	54.6	54.6	40.2	40.2	40.2	40.2	40.2
	3500	70.02	70.02	63	45	42	30	30	30	30	30
	4000	54.6	54.6	40.2	30	30	30	30	30	30	30
	4500	42.3	42.3	30	30	30	30	30	30	30	30
	5000	30	30	30	30	30	30	30	30	30	30
	5500	30	30	30	30	30	30	30	30	30	30
	6000	30	30	30	30	30	30	30	30	30	30
	6400	30	30	30	30	30	30	30	30	30	30
	7000	30	30	30	30	30	30	30	30	30	30

Time needed for diagnosis: 200 engine revs.

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