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2009 Corolla S will not start when it rains

My 2009 Corolla S will not start after rain. It cranks fine, but no start. Research points to a possible cracked dizzy cap letting moisture in and causing spark problems, but this car has a computer controlled spark with no distributor that I can find. Anyone have any ideas what may be causing this? I still need to get to work even on rainy days… I checked fuel pump and pulled one spark plug which seems to be sparking away.

Try replacing the coil-on-plug boots.

https://www.rockauto.com/en/catalog/toyota,2009,corolla,2.4l+l4,1442280,ignition,spark+plug+/+coil-on-plug+boot,10150

Tester

You’ve just GOT to stop using Lucas replacement electrical parts in the UK. Prince of Darkness, you know!

Just kidding, I think @Tester has the right idea. Next time it refuses to start, spray some starter fluid into the intake. If it starts for a moment and dies, it isn’t electrical. If it doesn’t fire, that is confirmation it is electrical.

Thanks, I will try the starter fluid. I checked that the fuel pump is providing pressure at the fuel pump, but could not think of a way to confirm it is getting all the way into the cylinders.

I don’t know much about how the starting sequence works, but wouldn’t all 4 coil on plug modules have to be shorted to not get any kind of start at all?

Yes, I think that’s true. I think the problem is electrical although it would be odd for all 4 coils to stop working when wet. And coil on plug doesn’t expose the spark plug boot. The separate sealing boots are cheap so it couldn’t hurt to just change the boots. I’d be looking at the crank and cam position sensors as well to make sure their electrical connections are clean and water-tight as well.