Fellas,

I've got this PowerQuest 280 with a 496MAG HO and a factory build M1 intercooled Procharger. So far, it's been golden. But then, we pulled the ultimate bonehead boater's move and dropper it in without the drain plug. We were out of routine. Don't judge... We got it back on the trailer, but it it took keeping it on at full throttle, plowing around the inlet to the ramp area until the wife could get the trailer back into the water. Luckily, there was nobody at the ramp, so no harm, no foul. After letting it drain, we dropped back in, drain plug in, of course, and headed out for an evening cruise. Upon exiting the no wake zone, I throttled up as I usually would, but the boat didn't want to get out of it's own wake. It took forever to climb up on a plane. A few details... First time with a full load of fuel. First time with this many people (four adults, two of them fairly good size, two small children). typical 496 transom soot seems excessive after this event. Take-off power seems off considerably, even with lighter load (fuel and people). Fuel consumption seems excessive, although this is the first time we've made an extended trip with this boat (and hour or so, one way, at modest cruise speed). Obviously boat seems to run fine once it's on plane. One service shop suggested new spark plugs, which I've done. While the engine seemed to like them, the issue is still there, even if slightly improved (maybe). Old plugs seemed slightly fouled, but not horribly. Center electrode seemed very small, as if eroded, but pics of the Denso plug seemed to indicate they are made fairly small. New plugs, ACDelco 41-983, had much more substantial center electrodes. I've spoken to Mercury. I've spoken to a total of three shops. I've gotten suggestions about the O2 sensor(s) and I've gotten suggestions about a locked open injector. Both seem like reasonable possibilities, but I'm not of the mind to just start throwing parts at it. With the intercooled Procharger, the intake for the engine is actually pretty low in the engine well, and I wonder about ingesting small amounts of water as it sloshed around while the boat was loaded down with the drain plug missing. I have not had a chance to plug into the ECM and see if there are any codes, but I have gotten a commitment from one of the local Mercury service shops to do so. I wouldn't be about purchasing one of these scanners for my own, if they aren't to spendy, but I'm not really sure what to get. My last boat had an old school 454 carb engine. This is my first go with a "smart" engine. Don't know if the attempted sinking, or the subsequent heavy load plowing had anything at all to do with this, but the coincidence is there. That's when the behavior changed and the performance dropped off. While planing, the tach hits a wall at 2900 RPM until the hull starts to break loose. After that, I can put it wherever I want it within it's normal RPM range. While planing, boost gage shows zero manifold pressure at that 2900, which is different from on a plane, where it hits zero manifold pressure at about 3700 RPM.

Thoughts?

Thanks. Brad.
Model Machine and Precision LLC
(937)545-8991

are you sure that the belt was not wet and slipping? that would give a low boost issue. it would take enough water to sink the boat in order to really ingest any water that should be a problem plus you say it runs once it is up so engine is probably fine.

MerCruiser 496 MAG HO | ProCharger

FWIW,

This is pretty much my exact setup. I provide this to illustrate how low the intake is. I don't realy think we had THAT much water in the boat, but I'd think enough could get in to potentially toss some into the bellmouth of the ProCharger. Not enough to hydrolock the engine, but, maybe, enough to kill an O2 sensor. Not really sure how much it takes to do that, or even if any would make it through the combustion tract. Just adding food for thought.

Thanks. Brad.
Model Machine and Precision LLC
(937)545-8991

Comp,

I'd think the belt would either dry out and stop slipping or burn its way through. Don't have any real basis for this assumption. Just what I think is logical. Not discounting anything.

Thanks. Brad.
Model Machine and Precision LLC
(937)545-8991

Does the engine even have 02 sensor and is the engine running in closed loop if so?

Underpsi,

It has always been my assumption that these EFI engines couldn't NOT have O2 sensors. Seems like I read a discussion thread a number of years ago where somebody was asking if EFI could be installed without one; if a baseline could be established with the sensor, and then remove the sensor, because of the whole water issue, and the resounding answer was "No". To be honest, I really don't know. This is about 83 steps above my paygrade in the field.

Thanks. Brad.
Model Machine and Precision LLC
(937)545-8991

Some EFI systems run without an O2. They run a preset program based on engine load/ throttle position/ eng temp. If it is a feed back system then it has to have O2 input.

Guys,

Just got off the phone with Mercury Tech. After tracing the engine serial number, we've determined the engine has temp sensors, not O2 sensors. Don't know if the temp sensor could be the culprit, if we're now looking at the injectors or something else entirely. Any advice is more than welcome.

What am I looking for if I want to pick up a code reader of my own?

Thanks. Brad.
Model Machine and Precision LLC
(937)545-8991

When back, did you tiot trailer up as humanly possible in case eater got up frt where maybe not set up to easily drain ? I use a farm jack, others use steep hill near the house, just to do once in a while. I know one person who forgot his drain plug and smartly brought it up nearby shallow water beach.

Btw, if anything was under water, it eas most likely your starter and of course the connections on it.