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) |
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- 180 Degree Interval Difference Method
- 360 Degree Interval Difference Method
- 720 Degree Interval Difference Method
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- NG judgment for exhaust gas misfire
- NG judgment for catalyst-damaging misfire
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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.
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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)
|
 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 |
 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.
|
JUDGMENT VALUE SPECIFICATION
| 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.
JUDGMENT VALUE SPECIFICATION
| Malfunction Criteria |
Threshold Value |
| Catalyst-damaging misfire diagnostic value |
Value of Map2 or more |
INTAKE AIR AMOUNT - MAP2
| |
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 |
| 100 0 rpm |
80 |
80 |
80 |
80 |
66 |
66 |
50 |
40 |
| 150 0 rpm |
80 |
80 |
80 |
80 |
66 |
66 |
50 |
40 |
| 200 0 rpm |
80 |
80 |
80 |
80 |
66 |
66 |
50 |
40 |
| 250 0 rpm |
66 |
66 |
66 |
66 |
57 |
50 |
36 |
26 |
| 300 0 rpm |
66 |
66 |
57 |
57 |
50 |
44 |
26 |
20 |
| 350 0 rpm |
66 |
66 |
50 |
50 |
36 |
26 |
22 |
20 |
| 400 0 rpm |
66 |
66 |
50 |
44 |
26 |
20 |
20 |
20 |
| 450 0 rpm |
57 |
57 |
44 |
40 |
26 |
20 |
20 |
20 |
| 500 0 rpm |
50 |
50 |
33 |
26 |
22 |
20 |
20 |
20 |
| 550 0 rpm |
40 |
40 |
26 |
22 |
20 |
20 |
20 |
20 |
| 600 0 rpm |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
| 610 0 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.