M42 + Water Do Not Mix

[SSE30]

Hi everyone,

Sadly, I think I destroyed my M42. Sucked up some major water during a flash flood. Plug wells were filled with oil/water. The car did not hydrolock as far as I know. Ran shittily and wouldn't hold idle after.

Compression numbers are good in cylinders 2-4 at ~190PSI. Cylinder 1 is around 160.

Can I expect this engine to run well again without major repair? Am I delusional?

Thanks a lot in advance.

[bmwman91]

I wouldn't worry about the spark plug holes too much. The oil is probably from the notoriously leaky valve cover gaskets. Did you drive through 3ft deep water, or was it just raining so hard that a ton of water pushed into the engine bay as you were driving?

Chances are that the engine is fine, mechanically. If I had to guess, the bad idle is either because water messed up the AFM (and you probably just need to dry it out), or because water went through the combustion chamber and flash-cooled the O2 sensor which is really bad for it. You could also have a wet wiring harness, or some water in the plastic wire box that sits under the intake manifold.

If you had hydrolocked it, it would not be running at all. The bad idle...does it stall if you let off of the gas? Is it only on cold starts, once the engine warms up or both?

Your compression numbers seem OK. The original engine in my 318iS had similar numbers (cylinders 1-3 were 210PSI, cylinder 4 was 160PSI) and it ran great for 70K miles like that (until the timing chain came loose lol).

[DER E30]

I wouldn't worry about the spark plug holes too much. The oil is probably from the notoriously leaky valve cover gaskets. Did you drive through 3ft deep water, or was it just raining so hard that a ton of water pushed into the engine bay as you were driving?

Chances are that the engine is fine, mechanically. If I had to guess, the bad idle is either because water messed up the AFM (and you probably just need to dry it out), or because water went through the combustion chamber and flash-cooled the O2 sensor which is really bad for it. You could also have a wet wiring harness, or some water in the plastic wire box that sits under the intake manifold.

If you had hydrolocked it, it would not be running at all. The bad idle...does it stall if you let off of the gas? Is it only on cold starts, once the engine warms up or both?

Your compression numbers seem OK. The original engine in my 318iS had similar numbers (cylinders 1-3 were 210PSI, cylinder 4 was 160PSI) and it ran great for 70K miles like that (until the timing chain came loose lol).

This, dry it out and it will probably be OK

[SSE30]

I wouldn't worry about the spark plug holes too much. The oil is probably from the notoriously leaky valve cover gaskets. Did you drive through 3ft deep water, or was it just raining so hard that a ton of water pushed into the engine bay as you were driving?

Chances are that the engine is fine, mechanically. If I had to guess, the bad idle is either because water messed up the AFM (and you probably just need to dry it out), or because water went through the combustion chamber and flash-cooled the O2 sensor which is really bad for it. You could also have a wet wiring harness, or some water in the plastic wire box that sits under the intake manifold.

If you had hydrolocked it, it would not be running at all. The bad idle...does it stall if you let off of the gas? Is it only on cold starts, once the engine warms up or both?

Your compression numbers seem OK. The original engine in my 318iS had similar numbers (cylinders 1-3 were 210PSI, cylinder 4 was 160PSI) and it ran great for 70K miles like that (until the timing chain came loose lol).

Holy shit man. This gives me hope.

I was going down a hill during a flash flood (way too fast mind you) parallel with a truck. We reached the trough of the hill at the same time and he splashed a metric shit ton of water into the intake side of my grill. It started sputtering after that so I feathered it around 3-4k RPM to keep it from hydrolocking. Got it all the way home running like absolute crap.

I took the plugs out, cycled the pistons to get any water out (there was maybe a tablespoon in one or two cylinders, if that).

The plugs and plug wires are toast (oil all over them) but I cleaned them and put in new plugs and those fouled.

Still to do:
New plug wires
New Plugs
Possibly a new VC gasket (what do you guys think?)
AFM is good, checked on another M42.
02 i suppose.

[SSE30]

When I say bad idle, I mean misfiring and won't stay on unless gassed.

Im attributing this to the bad plug wires which are fouling the the plugs.

Also I still have to change the oil.

[Josh1254]

Unplug electrical connections that got wet. Let it dry out. It should be fine

[5Toes]

my m42 is currently running the same way. I think my plugs are fouled, or the crank sensor is intermittent. your crank sensor sounds fine if it ran all the way home.

start with ignition and go from there definitely.

[SSE30]

my m42 is currently running the same way. I think my plugs are fouled, or the crank sensor is intermittent. your crank sensor sounds fine if it ran all the way home.

start with ignition and go from there definitely.

Cool, will do. Just ordered new Bosch wires.

Hope you get yours running.

[varg]

My car misfires until it dries out if I drive through a deep puddle. Compression numbers could be cause for concern, maybe a cracked valve is not seating correctly, I was informed that it does happen with these engines when I had my cylinder head rebuilt.

[SSE30]

I got it running like new!

For future reference by anyone having the same issue:

Suck any remaining oil/water from the cylinders
Clean spark plug wells thoroughly
Replace spark plugs
Replace spark plug wires
Change oil

Pretty basic procedure, but it worked flawlessly. Thanks to everyone that helped.

[Dirty325ix]

Badass :ST1G:

[SSE30]

Update: M42 blew up 4 months after fixing water damage. Huge hole in the crankcase. Oil and metal all over the road. The end of an era.

Turns out water will significantly shorten your engine's life span.

Deciding If I should do a M30 swap or just throw in a healthy M42.

[roguetoaster]

Pics?

Install another M42 for now, and build an M30 if you have space. A little Hartge treatment goes a long way. Large valves, sporty cam, smaller intake manifold, header and maybe Megasquirt to get rid of Motronic.

[SSE30]

Pics?

Install another M42 for now, and build an M30 if you have space. A little Hartge treatment goes a long way. Large valves, sporty cam, smaller intake manifold, header and maybe Megasquirt to get rid of Motronic.

I'll post some up soon. It's nasty.

I think I will put in another M42. Quick and relatively easy I suppose.

I was even thinking about doing an M42 turbo. Always thought that was a cool setup but people seem to have so many issues with them.

A nice built M30 is a great option too but now that I think about it, it may not be the most practical or responsible thing given my cars mileage.

[AndrewBird]

You probably DID hydrolock the engine and bent a rod. Did the exact same thing in a MK2 Jetta I used to own. Went through a deep puddle, hydrolocked it, got it back running after a oil change, then 2 weeks later it blew TWO holes in the block.

For future reference, running the engine AT ALL with water in the cylinders will damage it. Also, if it has been run after getting water in, there won't be any more later. If there is, it means you have a blown head gasket and coolant is getting into the cylinders. The combustion process will vaporize any small amount of water and it will go out the tailpipe.