Today we crossed Lake Michigan for the first time with our 38 Commander - 90 miles.  It took three winters to get her to this point which feels great.   Two pictures are attached as she sits in Wisconsin now.

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The vessel is powered by 454 crusaders.    As we came across we heard some back fire (or could have been misfire) on the port engine.   It was an intermittent single pop sound and we could see some mist coming out of the flame arrestor.   This happened more at lower RPMs and less at 3,100.   However the engine did periodically drop RPM at cruise speed, and the same thing started happening to the starboard engine, but back fire was not heard.   Several times the RPM went to zero and the engine died.   Both engines did it at different times during the trip.   The engines have electronic ignition,electronic fuel pumps, new coils, and alternators.   I am curious if anyone has suggestions on what could be the problem?  I've got a new mechanic that's going to look at it.   Also installed new fuel tanks over the winter.

Thanks,

Mark

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Chris, the tanks were custom ordered and professionally installed so I would like to think so, but how to know for sure? I presume my mechanic knew what they were doing.

Mark, what about a digital RPM gauge. That will allow you to determine if the engine is actually fluctuating or if the gauge is inaccurate. $20.00 at Amazon. If it is the gauge swap the two and see if the problem follows. I'd like a bit more information on the damage to the engine wiring harness you mentioned. If you have two or more wires shorting together that could certainly be the root of your problem.

My tanks are new, but not sure about the fuel lines.   I checked with the marina and they claim the tanks are properly vented.    How would I find this anti-siphon device if installed in the fuel lines?   

Thanks,

Mark

Kevin, at one point the engine harnesses were removed and put back on.    Wires were cut when taken off.  The harnesses when put back on where spliced back together where the quick connect to the engine use to be.   

Thanks,

Mark

Mark---the anti-siphon pinhole is located about where the copper fuel lines come out of the tank(it has to be above the full fuel level). It is actually a screw-in carb jet that I guess CC repurposed for that function. The problem is not seen with mech fuel pump situations and seems to come into play with elec fuel pumps.. In my case I plugged the pinhole/jet and it immediately and permanently solved my engines running as you describe. It was causing air to be sucked into the fuel line and made the fuel mix way too lean. I think--but not positive-- that some newerboats have an electronic antisiphon device in line that is electrically operated to shut fuel off from the tank. It took us two hours to figure it out after my repower--but no problem since. If not related to that I would still look at grounds, etc as it happened after your boat was worked on and effects both engines.

Update on my problem.   Today I inspected my coils and found a broken quick connect clip.    I suspect this might allow the connection to vibrate and cause erratic RPMs after running a while.  I put a zip tie around the connection to keep it tight and the engine fired right up running perfect at idle.   I was not able to go out at cruising speed.

I then inspected the electric fuel pumps.   One pump has a positive from the ignition and a negative to the engine which I think is normal.   The other engine, the one giving me the most trouble, has a positive wire to the ignition, another spliced in wire to the positive going to the alternator, and a negative to the engine.   This alternator wire I don't think is right and I wonder if this could be the source of my problems.   Should I remove it?  No idea why one engine is wired different that the other.   Any advise?   I don't appear to have low oil pressure switches which I might install after I get this problem resolve.

Thanks,

Mark

Thanks to everyone for your suggestions.   I found the problem on my own with your help and some tinkering.    Turns out the problem was a lack of ground between the fuel pump/ignition and the starboard battery.   When I looked closely at the wiring I noticed one engine had a ground wire running from the bolt securing the coil to the engine going to the negative of the battery, this bolt is also where the electronic fuel pump and electronic ignition ground was connected.  The problem engine was missing this wire going to the battery.    I had a bad ignition module that once replaced went bad again and this led me to closely examine the wiring.    When this wire connection was made to match the starboard engine the two engines ran great.   I am hoping this solved my problem.   So the problem was first a bad ignition module, problem two was ground related.  The ignition module is very easy to replace and a $30 part.   If it goes bad you get no spark I learned.

Mark

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