Originally Posted by Bluegrass 7

Misfires only in OD at light throttle:
.
In OD the EGR is called to open allowing exhaust gas to flow into the intake tract, by design.
The purpose is to lower combustion chamber temperatures.
This action advances the ignition timing and reduces fuel injection amounts.
The results of this action is a very LEAN condition.
The Lean condition needs an ignition system in good condition due to the higher voltages required to fire the Lean mixture condition.
If any cylinder falls short on voltage, misfire will result under these specific conditions.
When the EGR closes from down shifting the EGR closes and conditions return back to lower voltages required to fire the standard mixture ratios.
Best way to find an offending coil is to look at stored data under mode 6, test 53.
This stored data is the misfire counts for each cylinder.
If any cylinder has high counts it likely is a cause of misfire and will not set a code.
The reason is the condition comes and goes with the driving condition so is actually cancelled as a possible code set due to it not being a 'hard' fault.
Bottom line is, do the testing before replacing parts.
Good luck.



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