January 19

A Really Ugly Spark Plug

Auto Repair, Car Maintenance


On Friday we had a seemingly straight forward diagnosis on a 2003 VW Jetta.

The check engine lamp was blinking and this indicates a serious concern, more specifically a catalytic converter damaging engine misfire. The engine ran very rough.

The conclusion of the diagnostic was that the concern was caused by bad spark plugs and ignition wires.

While performing repairs I found something very interesting: a spark plug with the ground electrode and center insulator completely gone. I suspect that these spark plugs were never replaced! Surprisingly they lasted for160,000 km.

good vs. bad sparkplug

Beyond the interesting spark plug wear was the diagnostic trouble codes stored in the computer. There were codes P0300, P0301, P0302 & P0303. Translating these codes in order are: Random cylinder misfire and misfire in cylinders 1, 2 & 3.

While all the spark plugs were worn none were as severe as #4 cylinder (that’s the one in the picture) and yet there was no code for a misfire in that cylinder.

About the author 

Bernie Pawlik

You may also like

2015 Mercedes C300, A Service

2015 Mercedes C300, A Service
{"email":"Email address invalid","url":"Website address invalid","required":"Required field missing"}

You might also like