Low power & rpm & rich exhaust smell

[bbethke]

This is a 2005 22V with a Marine Power Vortec 5700. For quite some time I had a problem that the boat would have full power and work great for about 45 minutes and then all of a sudden go to a reduced power mode where any throttle much above idle did little good. Exhaust smelled rich and rpm topped around 2500, not even able to get on plane. The next day the boat would take off full power again for about 45 minutes. I found a leak around the speedometer tube which allowed water to get into the bilge and my thought was that after 45 minutes there was enough water to splash around and hit a sensor and make it go into this "limp" mode. I fixed the leak and did a couple long runs and no problem.

Haven't been able to use the boat much for several months and now took it out and it is in this reduced power mode always now. I did pull the wire off each injector as it was running at idle and found that 5 injectors made the engine hesitate and then run slightly slower, 2 injectors made the engine hesitate and then run slightly faster and 1 injector made no difference (not even a hesitation) when it was pulled. Is this common? I suspected dirty injectors so I bought injector cleaner and put it in, but after over an hour of use (both idle and 2500 rpm) there is no difference and it still will not go on plane, most of the throttle does nothing, and top rpm is about 2500. It starts right up but even at idle sounds like it is running a bit rough. Are there any sensors that most often fail that I could try replacing first? I don't really want to go out and buy a $300+ scan tool for one time use, and I don't like the idea of paying big bucks and schedule for a marina to plug in their scan tool (probably would need to do it again after any repairs anyway). Any ideas out there?

[bbethke]

More tests and info to add

I haven't heard any tips to try from this forum yet, but I did do three other tests:

1) Pulled all the plug wires while idling and every one made a slight difference/hesitation when first pulled and then again when put back on, but rpm did not appear to change on any of them. Every one seemed to act the same.

2) Removed and inspected all the plugs. All had correct gap (.060), porcelain looked good, electrodes clean and all had the color of a working plug (not wet and not burned white).

3) Removed connector on every sensor, inspected to be clean and reinserted. I thought might have a bad connection.

4) Put a fuel pressure gauge on the rail connector and had 58 psi at idle, which was maintained at 58 when accelerating and while at the 2000 rpm which is the max I can get out of it now.

Any ideas of what else to try?