06 340 496s w/Bravo III drives with power on starter question

Korkie

Active Member
Feb 2, 2016
1,329
Leonardtown, MD Potomac River / Chesapeake Bay
Boat Info
2006 340 Sundancer, Garmin 7610, xHD 24 Radar, VV703, SeaStar Hydraulic Steer, Shadow Drive AP
Engines
Mercruiser 496 Mags
Bravo III Drives
Been having some intermittent power issues. ie. Brief loss of power to Smartcraft system and port motor. Like turning switch off and back on. Also some issues with brief loss of rpms on stbd motor. Pretty much ruled out fuel issue, still plan on putting pressure gauge on fuel rail to verify. While poking around, found that the 2 wires coming off the starter move somewhat freely. One motor is looser than the other, but both are loose. The heavy gauge red wire is tight on the post. The ones coming off the fuse that is attached are the ones that move somewhat freely.
Question is: Are these wires that are attached to the fuse supposed to be tight? Cannot really see much , but by feel - they appear loose. Not sure if the wires are loose on the stud or if the stud is moving as a unit in the mount. Difficult to get good view.
 
Ordered 2 of the fuses that are in question, just in case it is the studs. (returnable if not) Will be wiggling in there to remove, clean all contacts and replace if needed. Thanks.
 
I’m not sure I understand your issue. When you say “power” do you mean engine output Aka horsepower, or do you mean 12 VDC electricity? For either case I don’t know how loose wires on the starter motor would cause an issue. Might cause erratic starting, but after that engine would run and dc would not be interrupted.

Electrical, or engine interruptions would have to be caused by something else.
 
Been having some intermittent power issues. ie. Brief loss of power to Smartcraft system and port motor. Like turning switch off and back on. Also some issues with brief loss of rpms on stbd motor. Pretty much ruled out fuel issue, still plan on putting pressure gauge on fuel rail to verify. While poking around, found that the 2 wires coming off the starter move somewhat freely. One motor is looser than the other, but both are loose. The heavy gauge red wire is tight on the post. The ones coming off the fuse that is attached are the ones that move somewhat freely.
Question is: Are these wires that are attached to the fuse supposed to be tight? Cannot really see much , but by feel - they appear loose. Not sure if the wires are loose on the stud or if the stud is moving as a unit in the mount. Difficult to get good view.
Wires need to be tight. It feeds 12 volts up to the 50 amp breaker located on top of the motor. If you loose the 12 volts, engine and smart craft dies. My 320 has the same power and out drives as yours so I would assume the wiring is similar. I had a intermittent short in the wire running up to the 50 amp breaker. That wire bundle we close enough to the head and it melted thru the wire wrap and the insulation.
 
Replaced both fuses today. The one on the port motor, which is the motor that powers up the Smartcraft for both motors, had obviously gotten hot. The plastic insulator cap on the backside of the fuse was melted and the metal was discolored. May be because of poor contact due to being so loose. Test drive this weekend.
 
I’m not sure I understand your issue. When you say “power” do you mean engine output Aka horsepower, or do you mean 12 VDC electricity? For either case I don’t know how loose wires on the starter motor would cause an issue. Might cause erratic starting, but after that engine would run and dc would not be interrupted.

Electrical, or engine interruptions would have to be caused by something else.
The main power for the Smartcraft and port motor comes off a fuse that is mounted to the hot cable on the starter. Loose this primary power source and everything smartcraft and port motor related is dead.
 
The main power for the Smartcraft and port motor comes off a fuse that is mounted to the hot cable on the starter. Loose this primary power source and everything smartcraft and port motor related is dead.

I don’t think so. Starter motor is 12vdc, Smartcraft is 5vdc. Run 12vdc through SC and poof. (ECM meltdown) When I upgraded our 496 to Smartcraft the only connection I added was a SC cable that attached to the ECM and a sub cable that re-wired the fuel tank sender from the boat harness to the SC harness. On my engine there was a stub from the ECM because all the gauges were analog. The ECM connection is the origin source for both SC data and its power

I also know about the 5vdc issue because Mercury made a big deal about it. The risk was the fuel tank sender in the 12 vdc boat harness could create a pathway to introduce 12 volts to the 5 volt Smartcraft system. As a result I had to ensure the tank sender was isolated from the boat harness.

I don’t know what the fuse does, but it does not provide power to SC.
 
It provides the "clean" power to entire port side circuit. Turn the port batteries off and no port engine and no Smartcraft. This is a factory install. Not an add on. The authorized Merc service manager at my marina must be wrong. I will certainly show him your post and get his opinion.
 
It provides the "clean" power to entire port side circuit. Turn the port batteries off and no port engine and no Smartcraft. This is a factory install. Not an add on. The authorized Merc service manager at my marina must be wrong. I will certainly show him your post and get his opinion.
I didn’t think it was an add on, just that it couldn’t be power for SC because that originates in the ECM (or is it PCM?). And of course the voltage difference. As for being the input power for the ECM. It might be, but feeding the most delicate electronics from a circuit shared with a high draw source like the starter motor seems like an odd choice.

I’m going to look at the SC rigging manual to see if there is anything there. I don’t think I have a wiring diagram for the 496 / 8.1 itself but that might clarify what that wire does.

Henry
 

Forum statistics

Threads
112,942
Messages
1,422,697
Members
60,926
Latest member
dander88
Back
Top