M3 Convertible got wet, now barely cranks and won't start

[hooRAH]

So after a long hiatus from BMWs, I have a friend drop off a barn-find M3 that hasn't run in a long time and he needs a place to store it. Its an interesting story, but for another time. I got the car running, put a new battery in it, put a car cover on it, and parked it in my driveway.

I came back from a long weekend away after what I heard was torrential rain and discover the whole interior is wet. Obviously the car cover was subpar and the covertible top doesn't seal. I shop vac out all the water I can find in the floorboards and made room in my garage to get the car in there, but now it won't start.

When I first tried, the whole car was dead - not a single light came on. I put the battery on the charger (in the car) and came back a few hours later and the charger is showing the battery as charged, but the thing still won't start.

It turns over, but only once. It just does a single RRRR. Thats it. Feels like a weak battery.

Recalling that the main battery wires run under the rear seat, I pull up the rear seat to find even more standing water - gross. Vacuum up all of that and I still have the same issue.

The main power is clearly shorting out to the chassis and not getting enough power to the starter motor, but I don't know where to check next.

I'd like to put the top down during the day and let the sun dry it out, but it just keeps raining. I have a tarp over it for now to keep it from getting more water in but would really like to get it into my garage. I have the battery out of the car and on the charger overnight, so I can try again in the morning with a known charged battery.

[B328iC]

As you stated the car got extremely wet. Under the rear seat is some electronics. If it gets wet you will have a problem. You need to get the car indoors or at least under something that will prevent the rain from getting into the car. Thin covers and tarps won't work. The car needs to dry out completely. If you can raise the tonneau cover you will probably fine that area full of water as well. You will need to clear the drains for that area. get the car dried out and then see where you are.

[SimonJD]

There is a big chance that your dme got wet, there are water outlets behind your engine head, if they clog, water will gather beneath the wiper cowl. And this can flood your dme giving the symptoms you describe.
Pictured is a water outlet, and the dme which is located (us/eu) on the passanger side of the engine bay.

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[hooRAH]

Appreciate all the info. I'll look into the drains near the DME for the future.

So here's the update - it seems to be ignition switch related. If I very gently tick the key over to the start position, it will start every time now. If I manhandle the key and force it all the way over, I only get one bump of the starter and then it stops. At this point Im not sure if it had anything to do with the water after all. Maybe.

Anyway, I got the car in the garage and its been drying out for the past 3 weeks or so. Everything is dry at this point (although my garage is pretty cramped). I opened up the tonneau cover and got some water out of there as well.

I still need to do a post on the condition I found this car in and the work I put into getting it to run. Its in fairly nice condition for as old of a car its in.

[clabs]

HooRAH

Sounds like it is the water and resulting condensation that might be affecting the ignition switch - it was working ok before. Might be worth spraying some WD40 in the lock - that is quite a good water dispersant.

Anyway - looking forward to some pics because it sounds like a great project.

Good luck with it mate.

Mark