Losing power while running on plane. Not HP but 12 volt power.

[maxum3300]

Hello all. I just had my motors replaced in my Maxum 3300 with 2 mercruiser 357 magnums. Last week while running on plane my starboard engine rpm would drop anywhere from a couple hundred rpm to as much as 1000 rpm and then just as quick it would pick back up. The next time it did it I saw all my gages go to 0 as well as if it wasn't getting power from the battery. I stopped the boat and checked all my battery connections. Unknowing to me that I shouldn't be using wing nuts on my battery terminals. A friend I had on board pointed it out to me and we tightened them as tight as we could. Started the boat back up and made it to the restaurant with no more problems. Coming back ask was fine as well until I opened the motors up to show my buddy what these motors were capable of doing. As I backed down to idle the starboard engine shut off. I went to neutral and tried to start the engine. No power to the key. No buzzer, nothing. Idled the boat to the dock and got down in the engine compartment. The battery cable to the starter was loose. I could move it by hand very easily. The next day I tightened the cable to the starter and replaced all the wing nuts with stainless steel nuts and lock washers. Well this weekend took the boat back out and rode to a local hangout, about an hour trip with no problems. Hung out on the anchor overnight for 2 days. Yesterday coming back everything was fine until I throttled back. Again the motor shut down and no power to the key. This time the 50 amp breaker on the top of the motor tripped. I reset and it started fine. Continued on my way home and again the power and rpm was dropping and picking back up until finally it dropped and cut off and again no power to the key. The breaker did not trip this time. Turned the key to on and jiggled the ground wire and the buzzer started. Got power back but tried to start it and it wouldn't and buzzer went dead again. Idled back on one motor and it was too late to mess with it last night. Assuming that since the starter wire was loose maybe the ground cable was loose too. I checked it this afternoon but the ground cable is tight. Started the motor and ran fine at the dock. I will say that I didn't have any problems all weekend until I hit some choppy water and the boat was bouncing quite a bit. I'm assuming something is loose but I don't know what else to check. I should add that when I replaced all the wing nuts I cleaned all the cable ends up with a wire brush. Any ideas what else to check. The motor is under warranty but I'd like to fix this myself rather than waiting for the dealer to come to me. It's a 35' boat so I am unable to take it to them.

 

[nola mike]

You've probably worn through some insulation on a wire somewhere. It's grounding out every once in a while. Guessing that when the engines were replaced the wiring was routed somewhere that's causing it to rub on something.

 

[alldodge]

Replaced your engines and prior to this you had no issues with your charging system. Now after the install you have power problems. So unless you or another person(s) put the engines in then your installer is at fault.

Now if you want to do all this yourself, then start at the batteries and start checking everything to make sure it is clean and tight.

 

[nola mike]

Tripping the fuse makes me think that he's got a short. Loose connection shouldn't do that.

 

[maxum3300]

It only tripped the breaker the one time and I'm not 100% certain that it tripped I pressed it expecting to hear a click but I didn't. I assumed it was tripped because it started immediately after I pressed it without touching anything. I don't think it is a wire harness issue because the motor is complete turn key. Drop it in and go so the harness is brand new. Tomorrow I plan to trace ask the wiring from the round plug out to the ends of each wire. Any other ideas or things to look for while I'm in there. As I stated before I've already checked cleaned and tightened all connections at the batteries. The old motor overheated blew a head gasket and had water in several cylinders. Prior to that the battery was new just replaced this spring. Is it possible that trying to crank the blown motor with water in the cylinders damaged the battery? It did heat up the starter. I have just over 10 hours on this new motor. 3 outings on it at roughly 3 hours each trip. First outing no problem. 2nd outing is when I first found the problem. Thought I had it fixed after I replaced the wing nuts with SS nuts and lock washers and tightened the cable to the starter because on the 3rd putting everything was fine out the way out in calm water. Problem didn't resurface until on the way back we hit some chop and bounced the boat around a bit. It may just be a coincidence that the problem resurfaced in the chop.

 

[wahlejim]

Sure sounds like a short somewhere to me. A wire is exposed somewhere that is shorting out with the bounce of the boat causing it to contact something. Momentary contact would account for momentary loss of power. Prolonged contact would cause the breaker to trip and the engine to cut out. To be sure it is not the battery, it is very simple to load test it and test the charging system in one test. Might take all of 5 minutes with a tester.