Diagnostic Aids

The EGR valve chart is a check of the EGR system. An EGR pintle constantly in the closed position could cause detonation and high emissions of NOx. It could also result in high long term fuel trim values in the open throttle cell, but not in the closed throttle cell. An EGR pintle constantly in the open position would cause a rough idle. Also, an EGR mounted incorrectly (rotated 180°) could cause rough idle. Check for the following items:

• EGR passages: check for restricted or blocked EGR passages.
• Manifold absolute pressure sensor: a manifold absolute pressure sensor may shift in calibration enough to affect fuel delivery.