EGR Flow Check

Chart C-7:

EGR Solenoid Circuit:

CIRCUIT DESCRIPTION:
A properly operating EGR system will directly affect the air/fuel mixture requirements of the engine. Since the exhaust gas introduced into the air/fuel mixture cannot be used in combustion (contains very little oxygen), less fuel is required to maintain a correct air/fuel ratio. If the EGR system sere to fail in a closed position, the exhaust gas would be replaced with air, and the air/fuel mixture would be leaner. The ECM would compensate for the lean condition by adding fuel, resulting in higher block learn values.

The fuel control in this engine is conducted within 4 block learn cells. Since EGR is not used at idle, the idle cell would not be affected by EGR system operation. The other block learn cells are affected by EGR operation, and when the EGR system is operating properly, the block learn values in all cells should be close to the same. If the EGR system becomes inoperative, the block learn values in the open throttle cells would change to compensate for the resulting lean mixtures, but the block learn value in the closed throttle cell would not change.

The difference in block learn values between the idle (closed throttle) cell and cell 2 is used to monitor EGR system performance. When the difference between the two block learn values is greater than 12 and the block learn value in cell 2 is greater than 140, Code 32 is set. The system operates in block learn cell 2 during a cruise condition at approximately 55 mph.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. Codes should be diagnosed using appropriate chart before preparing a functional check. If Codes 14, 21, 23, 32, or 33 are set, use those charts first.

DIAGNOSTIC AIDS:
This chart is a functional check of the EGR system. If the EGR system works properly, check other items that could result in high block learn values in block learn cell 2, but not in the closed throttle cell.