Subaru 2006 Legacy, Manual

Page: 1322 / 4302

GD(H4SO U5)-96
Diagnostic Trouble Code (DTC) Detecting Criteria
GENERAL DESCRIPTION
3. GENERAL DRIVING CYCLE
• Detect misfires from idling to high rpm.
• Perform the diagnosis continuously.
4. DIAGNOSTIC METHOD
When a misfire occurs, the engine speed will decreased and the crankshaft position speed will change. Cal-
culate the interval difference value (diagnostic value) from crankshaft position speed by the following formu-
la, and judge whether a misfire is occurring or not comparing the calculated result with judgment value.
Counting the number of misfires, if the misfire ratio is higher during 1000 rpm or 2000 rpm, judge correspond-
ing cylinders as NG.
As shown in the following figure, pick a cylinder as the standard and name it omg 0. And the former crank-
shaft position speed is named omg 1, the second former crankshaft position speed is named omg 2, the third
is named omg 3, etc.
Diagnostic value
calculation
(Calculate from
angle speed)
→
Misfire detection every
single ignition
(Compare diagnostic
value with judgment
value)
→
NG judgment (Misfire occurrence judg-
ment required by the law) (Compare
number of misfire with judgment)
• 180° Interval Differ-
ence Method
• 360° Interval Differ-
ence Method
• 720° Interval Differ-
ence Method • FTP1.5 times misfire NG judgment
• Catalyst damage misfire NG judgment
(A) Ignition order (B) Crankshaft position speed
EN-01774
#3 #2 #4 #1 #3 #2 #4 #1 #3 #2 (A)
(B) omg0 omg1 omg2 omg3 omg4 omg5 omg6 omg7
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