Failure mode - Ford Triton gasoline (Super Duty / Excursion / E-Series)

Ignition coil (COP) failure / misfire

Reliability tier: verified - verify before ordering, see /disclosure/

Symptoms

random cylinder misfire (P0300-P0308), worst in moisture/cold
rough idle that follows a specific cylinder; flashing MIL under load
cracked coil boot with carbon tracking down the plug well

Root cause

Coil-on-plug coils fail with heat cycles and age, and the boots carbon-track down the plug well - Ford dedicated three diagnostic bulletins to accurate COP misfire diagnosis on these trucks. A misfire on these engines is triage: coil, plug, or (3V) phaser/timing - the COP bulletins exist to separate them.

Diagnosis

swap the suspect coil to another cylinder: does the misfire follow? (classic COP bulletins' method)
inspect the boot for carbon tracking; check the plug while the coil is out
scan which cylinder; moisture-correlated misfires point to boots/tracking

Fixes

replace the failed coil(s) with the correct generation (DG-508 2V / DG-511 3V) and any tracking boot (coil replacement) - cheap parts; the diagnosis discipline (bulletins) is what saves money

Ignition Coil, COP (Motorcraft DG-508 2V era / DG-511 3V era)

while a coil is out: fresh plug of the correct generation (coil + plug) - marginal cost near zero; avoids the second access job

Prevalence

very-common