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I drove through a puddle and now my car is broken.

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So today driving home from school I got stuck in a puddle. The engine didn't stall nor did it hydrolock. It started running rough from the water mist on the maf so I shut it off to prevent a hydrolock. The water eventually reached the floor mats. Unsure how high it actually got. I doubt it reached the interior fuse panel because everything i checked works so far. Well except the engine. I think the ECU might be screwed. Idk where it is on this car but I believe the fuel injectors are firing even with the car not running. When I first tried to start the car just cranked sounded good. Definitely has compression. I then unplugged the maf and attempted to start again and it fired and ran for about 10-20 seconds then shut off. It has not started again. I do smell gas though around the engine. I also hear a noise when the key is in the on position. I tried to listen for the fuel pump prime but instead it's overshadowed by some noise from under the hood. It's a new noise to me. It sounds like rapid tapping. So the first thing that came to mind is that it's an injector stuck open. Anyways I primed the fuel pump a couple times then attempted a start the car just cranked and eventually the motor stopped cranking. My guess is that a cylinder or two is full of gas. I forgot to try a flood clear but I don't think that would help if an injector is stuck open. I don't believe the starter has enough power to bend rods so I'm not concerned about that. I'm just confused as to what can cause an injector to be stuck open in such a fashion.
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Pretty sure you shouldn't need to clear a flood yourself since the engine continually drains fuel from the cylinders. The only time you could flood the engine is when you start it, and only if you have a faulty coolant temp sensor or some other issue that causes too much fuel to get sent into the cylinder. Try some starting fluid behind the MAF and rev the engine up to 3-4k and see if it stays running.


Also what kind of "puddle" is deep enough to reach your floor mats? It's a Subaru, not a duckboat... You probably shorted something. Even if it didn't reach the fuse box there's all kinds of other electronics lower in the vehicle.

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Stuck in water how deep? When you say water made it to the floor mats do you mean they got damp or they were submerged? Water didn't come in the door when you stepped out right? You'll have to verify all your fuses by the driver's left knee and in front of the driver's shock tower under the hood.


The computer is on the sloped part of the passenger footwell. You should pull the carpet back and see if it got flooded. It would be possible for a flooded computer to do silly things like fire injectors because the injector driver is shorted instead of because it's time to fire it. If it is wrecked, it's pretty easy to swap a new one in.


Once the computer is verified clean and dry, charge the battery and see if it cranks again. If it doesn't take out the spark plugs and crank it and see if gas shoots out.


That should keep you busy for a little while if it doesn't get it running. Then we can check back to keep going.



P.S. I once went through water deep enough for the back end to be bouyant and wash me three feet to the side. Momentum made water come up over the hood all the way to the washer jets, but the actual depth was less than half way up the doors. But I didn't stop in that water and the door gaskets kept the inside dry for the short time I was in there. (Turns out it doesn't matter if you know how deep the water is, erosion might have made it a lot deeper when you weren't looking.) It scared the crap out of me.

Edited by doublechaz
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Chaz is right. My bets reading what you posted is that your ECU is hosed. I've seen hurricane flood vehicles where the water level was at or below the door seal and the ECU is the first thing to go. It's stupid but I've seen Subarus flooded halfway up their doors but not higher than the seat bottom and they start right up as soon as you change the ECU and drain/refill fluids.


Take out the ECU, remove the screws from it's non-waterproof cover, and see if there's any water in it.


Second, remove your damn spark plugs before you continue to turn it over. You say you don't believe the starter has enough power to bend rods, and I disagree. A Subaru starter delivers 1.4kw (~2HP) of force at full cranking amperage. The more resistance in cranking, the more power (HP) the starter delivers. It is enough to bend or snap a rod, and even enough to push your steel wrist pin clear through a cheaply made cast aluminum piston. Worse yet, if no damage to the piston or rod occurs, you also risk mashing your rod bearings with the force causing you to have a spun bearing.


Finally, the compression chamber volume of a standard 2.5L motor is only 46.6cc and is even lower for the 2.2 at 41cc. That equates to just 1.5oz of fluid to hydrolock a motor. The cylinder volume on a 2.5 is about 615cc and with a max injector flow rate of 280cc/min a small drip in the injector can put enough fuel in a cylinder in just a few minutes to hydrolock a motor. Bad ECU Injector drivers, a short in the wiring caused by water in the engine bay or on the harness connectors, or a weak injector can all cause flooding.


When you look at the math of all of it, it's kind of scary to think that less than a mouthful of water could kill your engine.

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