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sprinkles08
sprinkles08, ASE Certified Technician
Category: UK Car
Satisfied Customers: 21571
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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I have a 3.8 2007 C2S and i'm getting misfires when cold on

Customer Question

Hi Mark,
I have a 3.8 2007 C2S and i'm getting misfires when cold on 1 & 3 and random (P0300, P0301, P0303). Today I have changed coil packs and plugs on cylinders 1 and 3 but still getting the misfires, any ideas before I take it to a garage?
Submitted: 11 months ago.
Category: UK Car
Expert:  sprinkles08 replied 11 months ago.

Hello and welcome to JustAnswer!

There are many possible causes for misfires including fuel injectors, localized vacuum leaks affecting only certain cylinders, cylinder sealing issues or possibly coolant entering the cylinders, assuming the spark plugs and coils can be ruled out.

You can use some carb cleaner to spray at suspected leak areas while the engine is idling to see if there is a vacuum leak, but a vacuum leak wouldn't usually come and go based on temperature, a valvetrain issue wouldn't usually happen only when cold either.

If it only misses when cold then I would more suspect injectors or coolant entering the cylinders. If coolant enters a cylinder while the engine is off or continues to during warmup until the head expands then it will cause a miss when cold. If this is the issue then you may note the coolant level has dropped and/or white smoke from the tailpipe on startup.

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