Subaru Legacy IV (2008 year). Manual - part 408
GD(H4DOTC)-82
Diagnostic Trouble Code (DTC) Detecting Criteria
GENERAL DESCRIPTION
3. GENERAL DRIVING CYCLE
• If conditions are met, it is possible to detect the misfires from idling to high engine speed. However, to
avoid excessive load or harm to the engine, perform diagnosis at idle.
• 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 revs. or 200 revs., Judge corre-
sponding 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)
o
Misfire detection every single ignition
(Compare diagnostic value with judg-
ment value)
o
NG judgment (Misfire occurrence judg-
ment required by the law) (Compare
number of misfire with judgment)
• 180° Interval Difference Method
• 360° Interval Difference Method
• 720° Interval Difference Method
• FTP 1.5 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