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Q: My car will not start - 2002 Saturn SC2

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My vehicle will not start when it is warm outside. It will crank and attempt to turn over, and sometimes will start for one or two seconds, then immediately sputter out and die. It has a brand new fuel pump/filter, as well as new O2 sensors. I will start just fine after dark, or when it is cool outside, and run without any issues. I can restart it multiple times, and it will turn over on the first try. I have tested it at multiple points in the day over the last three days, and the temperature outside is the only connection I can find in the problem.

My car has 95500 miles.
My car has an automatic transmission.

A: This is a common sign of a faulty ignition ...

This is a common sign of a faulty ignition coil. Ignition coils are coated with a varnish-like insulation that becomes brittle over time after being stretched and contracted repeatedly as the copper beneath them expands and contracts at a higher coefficient than the insulation. The insulation develops small fractures that open when heated and close when cooled. When open, they allow shorting of coil windings and decrease or eliminate the coil's ability to function.

This type of temperature cycling happens because every time you shut the engine off, the fan stops running, the coolant stops flowing, and the temperature under the hood rises. Every time you start the engine again, the coolant flows, the fans turn on, and the temperature drops. The areas in and around the tops of the combustion chambers, the exhaust manifolds, and the exhaust components are hundreds of degrees hotter than the outside temperature under the hood.

When this heat dissipates and is absorbed under the hood, it is trapped, causing this cycling effect. Components that contain heat sensitive materials include parts like coils, injectors, igniters, and some sensors. Any of these may be potentially subject to this same kind of heat problem which can be very difficult to trace.

I would recommend having an expert, such as one from YourMechanic, come to your location to take a look at your vehicle to properly diagnose your ignition system and determine if the ignition coil needs to be replaced.

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