Misfire After Heavy Rain or Car Wash (Coil Pack Water Ingress) | MyMechanic

What’s Happening in Simple Terms

Modern cars use ignition coils directly over spark plugs. If moisture enters the spark plug wells or coil boots, the spark escapes to ground instead of firing the plug. That misfire causes rough running, warning lights, and loss of power until things dry or are repaired.

• Rough idle/shaking engine right after rain or wash
• Hesitation/jerking on acceleration (worse at low RPM)
• Check Engine light on/flashing (active misfire)
• Strong fuel smell from unburnt fuel
• Smooths once dry, but recurs with rain/wash

Why Moisture Gets In

• Aged coil boots and hardened seals letting water seep in
• High‑pressure washes forcing water past seals
• Cracked/loose ignition components from past repairs
• Blocked drains/weather seals dripping water near coils
• Condensation forming during humid climate shifts

• Ease throttle, drive gently if drivable
• Don’t push hard—misfire stress can overheat converters
• Flashing Check Engine? Stop in safe place
• Don’t open coils in rain—can worsen ingress
• If misfire won’t clear, call roadside help

• On‑site misfire check and coil inspection
• Practical recovery: advice/drying methods if safe
• Safe towing if misfire severe/persistent
• Guidance: coil/boot replacement, sealing, drainage fixes

• Replace old coil boots & tube seals before trips
• Avoid high‑pressure engine bay washing
• Check drains/weather seals are clear
• Use dielectric grease lightly for seal (per OEM guidance)
• Service spark plugs on time—worn plugs strain coils

Real‑World Scenario

After a wash or heavy rain the car bucks and misfires? Stay calm, ease off, let it warm—often it dries out. But if the light keeps flashing or the engine shakes badly, stop and call MyMechanic for help before costly damage sets in.

• Misfire right after rain/wash = coil moisture
• Rough idle only, better with heat = drying out
• Repeats with every rain = seals or drainage failing
• Flashing light + strong fuel smell = stop & seek help

Frequently Asked Questions

Conclusion

A misfire after rain or a wash is common but avoidable. Stay calm, don’t force the car, and get professional support if it persists. MyMechanic helps Singapore cars in Malaysia with roadside assessment, guidance, and safe towing—so rain doesn’t ruin the trip.

Frequently Asked Questions