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91 Riviera Running Rough in Rainy Weather Only

Guest vlg

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Hi,i have a 91 Riviera 3.8L non supercharged that runs rough intermittently in heavy rain only.I drove the car on long trips when it,s dry or light rain,also during the 2010 NY snowstorm no problems.I replaced the plugs and wires already-no change.There,s no check engine light on,scan the pcm-no codes.It stalled in rain once yesterday but started right back up

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If you had bad ignition wires that were replaced you can have a problem with carbon tracking. Spark seeks the easiest path to ground. When the ignition wire is open the spark is strong enough to travel down the coil terminal to ground. This action will leave a trail of carbon where the spark traveled down the coil terminal. When the wire is replaced it becomes the easiest path to ground. When humidity is high the carbon track becomes the easiest path to ground. This creates the intermittent misfire. If the spark plugs were used with the bad ignition wires the plugs can be carbon tracked. The defective wire provides the clue. If the corrosion was at the plug terminal check the plug. If the corrosion was at the coil terminal the carbon tracking is at the coil terminal. There is no way to remove carbon tracking. The part must be replaced. Before you get too involved I would remove the plugs and inspect for cracks in the insulator. I've seen brand new spark plugs that have porous insulators. Look for a small black (carbon) dot on the insulator. Good luck.

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