Hey All - new to the forum here. Thank you in advance for your expertise with an issue I'm having.

I have a 2001 Model 288 w/ 496 Mag HO. Had her out on the lake 2 weekends ago and she was running like a top. That is until about 45min in, I noticed at cruising RPMs (3500 +/-) she begin to hesitate and cut out. I didn't pull back on the throttle and the problem worsened to the point that the boat came off of plane. Fortunately I was able to inch her back to the dock at a bit above idle speed. After cooling down an hour or so I emptied and re-installed the fuel/water separator and she ran good the rest of the day without any issues, although I didn't run her hard.

Since this happened I replaced the fuel/water separator, filled the tank w/ premium, and added a couple bottles of HEET to the fuel tank as I thought this may have been a water issue. Fast forward to this past weekend and I thought my problems were gone - that is until the exact same problem came about. Once again, this was about 45 minutes or so of cruising speed. After cooling down a bit, we took her back to the dock with no issues.

Without taking the boat into the dealership I'm not exactly sure what to do next. I'm a do-it-yourselfer so I prefer to get knee deep in the motor myself and pursue this issue. All gauges were spot-on and no alarms were sounding.

I would like to add that when the symptoms started showing the problem was very erratic. What I mean by that is, it didn't feel like it was starving for fuel. The cutting-out at cruising speed started with an occasional blip and quickly worsened. At one point it honestly felt like someone shut the key off at 45mph and turned it back on before the motor had a chance to completely stop. This made me feel like it was possibly more of an electrical issue than a fuel delivery issue. When I idled her back to the dock, occasionally i would ease into the gas to try and get her on plane - when I did this I noticed popping out of the flame arrestor. At one point she died, but it started back up and idled perfectly. That is, until I tried to plane out.

This is pretty much all I can tell you about the problem I'm having, and if someone could get me on the right track I'd be extremely appreciative. One other thing I noted is the buildup of soot in the transom, but I'm not sure how much out of the ordinary this is. She's always seemed to have a little bit of soot but I never considered it something to worry about.

Thanks again all - safe boating to you!
J

Might be your crankshaft sensor going bad and getting erratic. there was a definite problem with failure in these early sensors, the replacement units have only one O-ring insead of two as your original one has. If the dealer has a scan tool and he should have them also check for codes. You could have a loose ground or corrosion in a connection and this can act like your problem. also check the simple 10 pin plug at the engine and have that pulled apart, cleaned and lubricated with some light lubricant like WD40 or like. Some boaters have also found simple loose connectionsat the key switch at the helm and bad or loose connections on the lanyard safty switch.
Hope these ideas help, it should be a fairly simple fix.

Best Regards,
Ray @ Raylar

Thank you Ray for your response/guidance with this issue. I'll take a look at the engine harness & kill switch as well.

This may be a silly question, but is this something that can be troubleshot with an OBD II reader for a typical automotive application, or is this ECM a mercruiser-specific reader?

Thank you again!

OBD scanners will not read marine ECM's, they take marine scan tools to read them.

Best Regards,
Ray @ Raylar

Well Ray, you were spot-on with your crankshaft position sensor. I had the local marina scan it this morning and sure enough it detected a fault which reduced the percentage of power. When they told me the price of a new one I elected to do it myself, which is how I'll be spending my evening. Looking at the part online it appears to be a very simple swap - can you confirm what all is entailed by chance? I'd like to know what to put in my tool bag before heading down to the marina.

Thanks again for your help sir!

Sure, a little liquid wrench spray or similar penetrating oil and a small #10 metric socket and ratchet with medium length extension. -1/4" size ratchet and socket size is more than adequate.
Be careful pulling out the old crankshaft sensor. The early ones like yours had two o-rings and moisture would get lodged between the two o-rings, one near top and one near bottom and cause a lot fo rust in the crankshaft sensor bore in the iron block. (this is what actually caused these early sensors to fail) This can cause the sensor to lockup in the bore and if it is locked up and doing that and will not come out without to much small twisting & pulling (be careful). This is the reason for the penetrating spray oil to get some into the top of the bore free up some rust debris and allow you to rotate and lift and free the sensor without !SNAPPING IT OF IN THE BORE -WHICH IS A HUGE PROBLEM!
Once the old sensor is out, put a little oil or lube on the o-ring of the new sensor and push it in until the #10 small hold in bolt is pretty much centered in its threaded hole and the sensor is in far enough to allow the bolt to thread in by hand. Tighten the bolt lightly and plug in the connector and you're back in business.

Best Regards,
Ray @ Raylar

Problem solved! Thank you so much for your help!

Safe boating!

You are welcome. Glad I could help with your 496 issue.
Have fun, boat safe and enjoy!

Best Regards,
Ray @ Raylar

This issue is well known on the 2001 8.1 both in the GM truck and marine applications.

Good to hear you fixed it with minimal expense.