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.

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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

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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

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Exhaust gas misfire (misfire occurrence level which influences exhaust gas)

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	68 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 Map2 or more

MAP SPECIFICATION 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)	650r pm	80	80	80	80	80	80	80	80
	1000 rpm	80	80	80	80	66	66	50	40
	1500 rpm	80	80	80	80	66	66	50	40
	2000 rpm	80	80	80	80	66	66	50	40
	2500 rpm	66	66	66	66	57	50	36	26
	3000 rpm	66	66	57	57	50	44	26	20
	3500 rpm	66	66	50	50	36	26	22	20
	4000 rpm	66	66	50	44	26	20	20	20
	4500 rpm	57	57	44	40	26	20	20	20
	5000 rpm	50	50	33	26	22	20	20	20
	5500 rpm	40	40	26	22	20	20	20	20
	6000 rpm	20	20	20	20	20	20	20	20
	6100 rpm	20	20	20	20	20	20	20	20
(g/rev (oz/rev))

Time needed for diagnosis : 200 engine revs.

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