Logo

Sluggish engine

RickR90s

Contributing Member
I have a 2002 PCM Inboard (5.7L HO, Throttle Body fuel injection) in a MB Sports Tournament ski boat. I store the boat at my buddy's for the winter and recently took it out of storage.

The engine has 850 hours and has been totally bulletproof through the years (lots of passes through the slalom course) with normal maintenance by me. Before winterizing, oil was changed with a filter, new fuel control cell filter, new plugs with dist. cap and rotor. The tank was topped off with some Marine Stabil added. I didn't have the precise amount I needed so I added the rest of what I had, to treat about 10 gallons. I know, my fault. And finally, the engine was fogged.

That was last Oct.

This past weekend I fired it up for the first time and noticed a very rough idle. Putting in gear, the roughness continued and the boat was down on power, only revving to 3900 rpm, 40mph WOT. This boat usually accelerates like a Big Block muscle car, so something is definitely going on.

My first thought is fuel, being bad and not completely treated. Michigan uses 10% ethanol in all their "normal" fuel's so that's my first concern. Would "some" treatment be enough to keep the gas in good shape for that amount of time?

Your thoughts are appreciated.

RickR90s
 
a lot of unkonowns regarding the fuel...there is usually some margin built into the recommended amount so I'd say a big factor is how much you needed vs what was added.

Fuel aside, I'd be inclined to recheck the tuneup work done...could be a couple of plug wires not fully seated. also could be that one or more of the wires failed due to the R&R they experienced....If that all checks out, I'd verify adequate fuel pressure with the engine @ WOT, under load....
 
a lot of unkonowns regarding the fuel...there is usually some margin built into the recommended amount so I'd say a big factor is how much you needed vs what was added.

Fuel aside, I'd be inclined to recheck the tuneup work done...could be a couple of plug wires not fully seated. also could be that one or more of the wires failed due to the R&R they experienced....If that all checks out, I'd verify adequate fuel pressure with the engine @ WOT, under load....

Thanks Makomark,

I'll check everything again per your recommendations. I did start the engine in the driveway after the tuneup and all seemed fine (I know, not the same as a lake test), but I'll go though everything methodically. Both fuel pumps (low pressure and internal FCC pump) are relatively new, but a pressure check is in order. If I recall, a throttle body based system puts out 30psi.

RickR90s
 
The pumps may be new but won't make full pressure if the suction line lets air in (loose se clamp, etc).

I dont have access to my manual set (or your SN) so can't verify that spec...going from memory, that's a reasonable number for the later TBI setups. I'm sure somebody on the Mercruiser boat can verify the spec if needed - just give them your Engine description w/ the SN...
 
.......................
I have a 2002 PCM Inboard (5.7L HO, Throttle Body fuel injection) in a MB Sports Tournament ski boat. I store the boat at my buddy's for the winter and recently took it out of storage.

The engine has 850 hours and has been totally bulletproof through the years (lots of passes through the slalom course) with normal maintenance by me. Before winterizing, oil was changed with a filter, new fuel control cell filter, new plugs with dist. cap and rotor. The tank was topped off with some Marine Stabil added. I didn't have the precise amount I needed so I added the rest of what I had, to treat about 10 gallons. I know, my fault. And finally, the engine was fogged.
How was this engine fogged?

Fogging is a dynamic procedure whereby the fogging oil/solution is introduced into the intake system while the engine is operating.
The solution must be introduced equally into each manifold plane. If we miss one plane, we miss 4 cylinders!
The solution cannot contact the injector air sensors.
If you did fog this engine, and if the solution contacted an air sensor, it may affect performance.
(Mark, please verify this and feel free to correct me if need be)

If an oil enriched fuel was introduced into the fuel system, this is NOT fogging.... at least not in the conventional sense of fogging.


That was last Oct.

This past weekend I fired it up for the first time and noticed a very rough idle. Putting in gear, the roughness continued and the boat was down on power, only revving to 3900 rpm, 40mph WOT. This boat usually accelerates like a Big Block muscle car, so something is definitely going on.

My first thought is fuel, being bad and not completely treated.
High octane Non-Ethanol gasoline should make it through a winter without issues.
(sitting through one or two summer periods would not be good)


Michigan uses 10% ethanol in all their "normal" fuel's so that's my first concern.
That would be my concern as well!

Would "some" treatment be enough to keep the gas in good shape for that amount of time?
I would NOT use any treatments that contain alcohol.
Stabil, for example, does not contain alcohol and will protect against corrosion caused by ethanol-blended fuels


Your thoughts are appreciated.

Suggestion during winter lay-up.
Perform all of your winterizing tasks.... oil/filter change, draining down block/heads, exhaust system, remove seawater pump impeller, etc........., but perhaps wait to replace parts such as cap, rotor, sensors, etc, until re-commissioning in the spring time.
This way what you've done will be fresh in your mind, and will perhaps be easier to diagnose if you have an issue.


RickR90s
 
Back
Top