Logo
FULL SITE MENU

Motor shuts off but turns back on after trimming down

J

jsandefer

New member
I have a Mercury 150 EFI 2 stroke on my 1995 ProCraft. For the past year, it has been intermittently shutting off while getting on plane. I thought it was a fuel problem, but recently I found out that if I trim the motor down after it shuts off, the motor then turns right back on. In fact, if I hold the trim button down, the motor stays on. Now I’m thinking it is an electrical issue, but I don’t know what it could be.
 
Only connection between trim and throttle is in the control box. The wiring harness in the control box has been chafed to the point where the kill wire (assumption) is contacting the throttle/shift arm and grounding out the triggers. Open up your control and look around.

Otherwise you have a chafing problem elsewhere (assumption).
 
Texasmark said:
Only connection between trim and throttle is in the control box. The wiring harness in the control box has been chafed to the point where the kill wire (assumption) is contacting the throttle/shift arm and grounding out the triggers. Open up your control and look around.

Otherwise you have a chafing problem elsewhere (assumption).
Click to expand...
"Kill wire", as in the wire that's connected to the kill switch with the lanyard? That's the Ignition wire (purple) and the only thing that kills the motor is the switch when it opens. Or, maybe a connection is loose (on the purple wire near the rubber piece where everything passes from outside of the shroud to the interior).
 
When the key is in the "off" position, the ignition is grounded. The ground wire on the ignition switch is black. I think the other guy was telling you to look for chaffing on the purple wire to see if it's grounding on something.
I'd suspect either a problem in the control box or I'd look for wires getting chaffed or pinched as you raise/lower your motor. There's no "open" condition on your ignition switch. Once the motor starts, the battery no longer powers the ignition in any way. To shut off the motor, the ignition system has to be grounded. If your motor is shutting off by itself, you have something that's grounding the ignition system.
 
jimn said:
"Kill wire", as in the wire that's connected to the kill switch with the lanyard? That's the Ignition wire (purple) and the only thing that kills the motor is the switch when it opens. Or, maybe a connection is loose (on the purple wire near the rubber piece where everything passes from outside of the shroud to the interior).
Click to expand...
I didn't say anything about a purple wire which is switched 12v. My comment had to do with supplying a ground unintentionally to the trigger circuits. Read it again!
 
Oldsaltydog said:
When the key is in the "off" position, the ignition is grounded. The ground wire on the ignition switch is black. I think the other guy was telling you to look for chaffing on the purple wire to see if it's grounding on something.
I'd suspect either a problem in the control box or I'd look for wires getting chaffed or pinched as you raise/lower your motor. There's no "open" condition on your ignition switch. Once the motor starts, the battery no longer powers the ignition in any way. To shut off the motor, the ignition system has to be grounded. If your motor is shutting off by itself, you have something that's grounding the ignition system.
Click to expand...
If the voltage from the purple ignition wire is interrupted, the engine will definitely stop running because the coil's primary won't be energized. The wire that could stop the engine, and it used to be a cheap way for people to prevent their car being stolen, is to ground the tach wire. I wouldn't recommend doing this on a modern engine, but with an old points ignition, it definitely works.
 
You need to get a factory manual for that motor!! Poking around wires with no knowledge could cost you big money. Those ECUs are not cheap and the manual is cheap insurance.
 
Fire up your motor and remove the battery cables. It will still run. I know it will on OMC and Yamaha motors. My son had charging problems with his 70 HP Evinrude. We'd meet on a barrier island and spend the day. Sometimes his battery would be drained and wouldn't start his motor. I'd crank up my 115 HP Yamaha and then we would swap batteries. I'd remove my battery while my motor was running and pass it over to him and he would give me his dead battery. When we got to the boat ramp to take the boats out of the water, we would swap back. The charging system replaces battery voltage one the motor is running.
 
Oldsaltydog said:
Fire up your motor and remove the battery cables. It will still run. I know it will on OMC and Yamaha motors. My son had charging problems with his 70 HP Evinrude. We'd meet on a barrier island and spend the day. Sometimes his battery would be drained and wouldn't start his motor. I'd crank up my 115 HP Yamaha and then we would swap batteries. I'd remove my battery while my motor was running and pass it over to him and he would give me his dead battery. When we got to the boat ramp to take the boats out of the water, we would swap back. The charging system replaces battery voltage one the motor is running.
Click to expand...

That's great if the motor doesn't have an ECM and injection, but disconnecting the battery isn't good for those systems. A sharp spike (up or down) can make the ECM shut down.
 
Battery voltage is about 14 when running. That's because it's being charged by the charging system. The starting system that powers the motor once it's been started by the battery. When my trolling motor battery is completely dead, I crank up my motor, disconnect the battery cables and connect them to the dead trolling motor battery. The charging system is not only capable of running my 115 Yamaha outboard, but it also charges the dead trolling motor battery!
 
Now, I don't have fuel injection on my 1999 115 Yamaha, but it does have electronic ignition. 4 stroke fuel injected motors might be different. It would seem odd to me to have a charging system that keeps your battery charged while the motor is running , but that same charging system can't supply the power to run the motor on it's own. If the motor caused a constant drain on the battery, you wouldn't be able to make many stops and starts without having to put your battery on a charger constantly. Think about that a bit.
 
Back
Top