Diagnostic Method

When the misfire occurred, the engine speed is decreased and the crankshaft position speed will change. Calculate the interval difference value (diagnostic value) from crankshaft position speed, and judge whether the misfire occurs or not comparing the calculated result with judgment value.

Calculate the diagnostic value (from crankshaft position speed) Misfire detection every single ignition (Compare diagnostic value with judgment value)

• 180° Interval Difference Method
• 720° Interval Difference Method
• Pattern Recognition Method NG judgment (Judge misfire occurrence required by the law) (Compare number of misfire with judgment)
• FTP1.5 times misfire NG judgment
• Catalyst damage misfire NG judgment

For misfire detection, there are three methods such as 180° Interval Difference Method, 720° Interval Difference Method and Pattern Recognition Method.

• 180° Interval Difference Method, 720° Interval Difference Method

Transform the time needed for crankshaft movement from BTDC 65° to BTDC 10° into revolution. As the following, regard the revolution as MNX0. And then regard the former revolution as MNX1, the second former revolution as MNX2, and the third as MNX3, etc.

Use the detecting method below for misfire patterns, and judge misfire occurrence when the result calculated from the formula is out of threshold value.

180° Interval Difference Method (DDNCON0) 

Judge misfire when the (1) and (2) above are completed.

720° Interval Difference Method (DDNCYL0) 

Judge misfire when the (1) and (2) above are completed.

• Pattern Recognition Method

  Pattern Recognition Method has two patterns such as every time misfire on one cylinder and continuous misfire on two cylinders.

  Fig 4: Identifying Pattern Recognition Method

  Courtesy of SUBARU OF AMERICA, INC.

Every time misfire on one cylinder 

Calculate the simple average (calculate MNX 0 - MNX 1) per one hundred ignitions for one cylinder (per four hundred ignitions for four cylinder).

Regard the value calculated for #1 cylinder as AVE1, #2 cylinder as AVE2, and as AVE3, AVE4 like the same way. Judge misfire occurrence when the value calculated from the following formula is larger than threshold value.

(Max. value of AVE1 to AVE4) - AVEn (n=1,2,3,4) >= threshold value --> Judge that misfire occurs.

Continuous misfire on two cylinders 

1. Two continuous ignitions with "MNX 0 - MNX 1 >= threshold value" occurs.
2. Two continuous ignitions with "MNX 0 - MNX 1 =< (threshold value)" occurs.

Judge misfire occurrence on continuous two cylinders when the judgment criteria (1) and (2) above repeated for four hundred ignition.

• FTP 1.5 times Misfire (Misfire occurrence level which influences exhaust gas)
• Judgment Value 

  Judge malfunction when the misfire rate in 1000 revs. is large.

  Fig 5: Malfunction Criteria Table (1 Of 2)

  Courtesy of SUBARU OF AMERICA, INC.
  1. Time Needed for Diagnosis: 

     1000 engine revs.

  2. Malfunction Indicator Light Illumination: 

     2 continuous driving cycles.

• Catalyst Damage Misfire (Misfire occurrence level which results in catalyst damage)
• Judgment Value 

  Judge malfunction when the misfire rate in 200 revs (400 ignitions) is large.

  Fig 6: Malfunction Criteria Table (2 Of 2)

  Courtesy of SUBARU OF AMERICA, INC.
• Map 1 Fault criteria limit for misfire which would result in catalyst damage
  Fig 7: Identifying Result In Catalyst Damage Table

  Courtesy of SUBARU OF AMERICA, INC.

1. Time Needed for Diagnosis: 

   200 engine revs.

2. Malfunction Indicator Light Illumination: 

   Illuminates as soon as malfunction occurs.