Thoughts on what I broke?
 

I was out boating with the family last night. Second trip out for the season, first trip was flawless. This time we started out strong, cruised the lake, filled up the ballast tanks and surfed for 45 minutes or so. Drained the tanks and we were taking a final lap around the lake before leaving and this is when the problem started. The tanks were empty, we had 7 people in the boat and were cruising ~20mph or so. I remember there being a few sticks in the lake and slowing down and swerving to avoid one. When I went to throttle back up the engine was sluggish and firing poorly. I didnt have any lights or sounds from the dash, but the engine was HOT. Temp was around 230 and it usually lives at 170. Engine wouldnt go over 1500-2000 rpms, somewhere around there. Sounded fine at idle, but anytime I tried to throttle up it would just bog down and sound like it was occasionally misfiring. As best I could tell backfire/misfire came from the port side of the motor. Noticeable white exhaust coming up around swim deck, but nothing in the engine bay. Back in the marina it sat for a while and cooled down some while we replaced a bunk that floated off the trailer (it was a rough night). It started up just fine this time, sounded good at idle, but again, anytime throttling up the engine would bog down/smoke/misfire. Any thoughts on what this could be? I have it narrowed down to one of about two dozen things.... Boat is a 2004 MB sports with the PCM 330 in it.

Sorry for your problems with your boat!
Im no mechanic and I'll let someone else who knows more chime in but I'm gonna guess its either a fuel pump filter or your impeller is going bad?
Please post up the answer once you find out what it is! Best of luck!

If it were a mercruiser I would say cap and rotor.

Again, I'm not a mechanic, but it sounds kind of like your impeller. If they explode, you will need to clean out all the water lines as well and hope nothing is clogged.

Thanks for the ideas guys. The impeller is good though. It was replaced at the beginning of the season, and just for good measure I pulled it today to double check. Anyone know if this is something that could happen from the thermostat randomly deciding to stay closed? Engine overheats and goes into limp mode?

if the engine was overheating for some time and no alarms went off to warn you ...you could have blown a head gasket. The symptoms , white smoke sounds like water getting into the heads , and a loss of power. It is a simple task to check cylinder compression and would rule this out in about 30 minutes

check the scoop on the bottom of the boat

I had the same problem last year, minus the HOT engine temp and white smoke. I ended up have water in my fuel tank and water in the fuel filter. Unknown how water got in there?

Have you looked at your oil? Hopefully it doesn't look like chocolate milk.

Sounds like it went into LIMP mode to keep u from melting the head. Could be a lot of things. Happened to me last year and it was my oil pressure sensor that went bad.

also check water intake at the transmission cooler for debris

I would think it's just an Impeller and you just never paid that much attention to the amount of steam that comes out of the back of the boat normally. A lot people think its smoke and its just normal steam from the exhaust.

The impeller goes bad it over heats and goes into limp. You turn it off it cools down and you can crank it but it won't let you rev it because it's still in limp because it's still hot and can't cool off because there is no fresh water flowing through it.

No mechanic but it happen to me on my boat.

This may not be exact for your motor, just going off of memory from a couple of motors I have had, a merc and now an indmar, so forgive me if this is inaccurate for your motor.

Get a fake a lake hooked up to your raw water intake on bottom of boat. Run your boat to op temp, 170 as you stated. Shut off motor, check your motor oil and pray it is black/ dirty gold and the proper level, and not chocolate milk colored. If it is low on oil, add, if it is chocolate milk, then stop everything and take it to a boat mechanic. And I am sorry, that is not good.

Check the sea-water/raw water intake grate underneath the hull. Attach fake a lake, Pull the raw water hose going into your impeller off the pump housing, and make sure you can flow water up from there and it is clear of debris. If so, re-connect hose and move on.

Check the transmission cooler diverter/manifold, should be one of the first things you come to after water leaves the impeller pump, just follow the water hose from pump housing until you reach it. There is a screen on the bottom/intake side of this manifold. Pull the hose, then feel up in there to make sure it is clean metal, visually inspect it. If clear move on.

Loosen alternator mounting bolt, the one that pivots, then loosen the tension adjusting bolt and get slack in your belt. Pull belt off water pump pulley (the circulating water pump mounted on motors front, not the raw water/sea water pump with impeller in it). See if the pulley on the water pump spins... should spin freely. If not, you may have a failing water pump. If it turns "too freely" you may have a snapped water pump shaft, but you won't know till you pull it off. If everything seems normal, move on. While belt is off, loose, see how hard it is to spin your impeller pump, it should not spin easily at all, if it does, then your impeller pump is broken, or your impeller is spinning on the spline and needs to be replaced... prob not your issue as you have checked this already.

Pull water intake on top of engine to get to your thermostat. May have to disconnect a bunch of hoses.... It is a $10-20 part, so it is best to just change it while you are there, but take it out and put it in some water on stove and drop it it, bring water to boil to see if that t stat starts opening around 170 and then fully open before the water gets to boil. If it is stuck closed, or won't open all the way, then you will know it was bad.

Lastly, but hopefully you do not have to do this and you find the problem before, pull your circulating pump, make sure it spins freely, pull the back cover off, inspect the veins to make sure they are all there and you did not send chunks of metal down the line. Hold the pump veins from spinning and try to spin the pulley to see if the shaft is connected and intact. A 12 year old boat will prob have a lot of corrosion, so it may be best just to get a new pump along with the t stat, new pump is prob $50-100....

I do not know how to completely flush the motor and hoses of debris, but definitely do that too. After all this, if you still overheat, then It is way over my knowledge level and ability.

good luck.

Now this is an answer! Do you have any marital advice? Ha! Well done man!

sounds like its in limp mode from an overheat. check cooling system. may have to reset codes

lol.... thank you. And sorry, I have no marital advice. I am slowly learning that the old adage "happy wife equals happy life" is true. I just buy her flowers randomly but often.... she seems to really like that.

WHOA! Thank you for possibly the greatest answer ever. After spending some time in it and hooking it up to a computer at a dealer I learned there where no active codes. Compression checks revealed cylinders were good. Leak down test was good. So far smart money is on thermostat sticking closed, motor going into limp mode, and messing with the rotor and distributor a little bit. Gonna replace those things and it should be good. Hopefully. Aside from the hours of diagnosing it shouldn't be a big problem. Thanks for all the help and answers everyone. I appreciate the support and guidance.

this is the best of wakeworld, enthusiasts that just love boats and are willing to help others.

Another possibility for misfire is an overheat leading to detonation/pre-ignition, so it is good that your leak down was good.

I would bet money on something in your raw water system or like you said, a stuck thermostat.

Having dealt with this on a nearly 20 year old boat, it's gonna be nasty in there getting to your thermostat should you choose to do the work yourself. They corrode up pretty good