Slight Misfire / Breakup at High RPM - Missing Coil Pack Ground Wire

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Problem

Engine has a slight misfire or breakup under load that persists even after a full tune-up. The coil pack ground wire is missing or broken, which can occur during engine work such as a head gasket replacement.

Slight misfire that no one can seem to diagnoseEngine breakup under hard pull / at high RPMMisfire persists even after full tune-up (plugs, wires, etc.)Possible electrical shock when touching valve cover or coil pack plate

Root Cause

The coil pack ground wire was missing or broken. This wire grounds the coil pack mounting plate to the cylinder head via a small Phillips screw under the cylinder 5 high-tension wire receptacle and a bolt on the head. Without it, the plate can hold a charge and the ignition system may not fire consistently, causing intermittent misfires.

Confidence

Moderate confidence — Multiple community members agreed on this solution

View Original Thread →Posted September 2005 on SupraForums.com