Hi, I'm new to the forum here, but I think I'm in the right place. Let me also preface this by saying that I'm definitely not a mechanic, especially an outboard mechanic...
I have a Merc 225 EFI, 3.0 Litre outboard. Serial number begins with 0G28. Unfortunately, I can't find a model number. I know it's supposed to be on a silver plate on the mounting bracket, but either it's gone or I'm daft... probably the latter of the two.
The old battery was absolutely shot, old and dead and was not disconnected when the boat was put into storage.
Installed a brand new battery and noted that I got some spark when connecting the terminals.
I turned the engine over just to make sure it would crank. No ears on, so I didn't attempt to start it.
Everything was left turned off and key out of the ignition and it drained a brand new battery in less than 18 hours.
With ignition and all accessories "off" and battery disconnected, I put an ohm meter to the two heavy gauge wires running to the engine. The result is almost no impedence (short circuit?)
I pulled the elecrical cover on the starboard side of the engine to reveal the starter relay, etc. The main positive connects to the bottom side of the starter relay, along with 5 other wires. I pulled this loose and tested the individual wires for short circuit. I got no impedence on a medium guage red wire that runs directly to the alternator. Also got no impedence on one other wire. I was unable to trace it with absolute certainty, but I believe it went to the power trim system.
In short (don't mind the pun) - I think this is probably a bad rectifier. But for the life of me, I can't find the thing!! Can someone please confirm if my suspicions are likely correct? If so, where is the rectifier? (Pictures and/or detailed instructions would be greatly appreciated. Once I have located and isolated the rectifier, how do I test it?
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UNDER THE COWL:
I thought a description of what's under the cowl might help ID the engine. If that's not necessary, please ignore this entire section.
There are two EFI computer modules, one above the other, on the rear of the engine. 3 Coil pack and three plugs on the left and 3 coil packs and plugs on the right. There's an electrical compartment with cover held by 3 screws on the starboard side. Underneath is a starter relay, what appear to be 2 other relays (possibly power trim?) The small cover for that compartment has a single blade fuse on the outside.
The alternator is mounted on the top of the engine, toward the rear. There is one medium guage red wire with a boot and a small plug of some sort with 2 wires coming out (one is purple.)
The front of the engine is a solid aluminim plate held on by some large allen-head screws.
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Thank you in advance for any assistance!
UPDATE!
Ok, so it seems the rectifier is built into the alternator. If I ground the (-) side of my ohm meter to the power head and place the (+) terminal to the copper bolt sticking out of the alternator, I get a reading with a small amount of resistance. If I switch the terminals and place the (+) side of the ohm meter on the block with the (-) probe on the copper bolt, I get no reading (infinite resistance.) To the best of my understanding, this is correct in that the diodes of the rectifier are working properly and only allowing power to flow in one direction, turning the AC current into DC current.
So... not the rectifier/alternator? However, it seems that with the ignition in the off position, there should be some sort of relay that prevents this flow of power so as not to drain the battery. I'm a bit stumped here, but I moved on.
There is some sort of small sensor/device on the Starboard side of the carb. housing that has 4 leads plugged into it. This device also seems to be allowing power to flow from positive to negative when plugged in. I have no idea what it is/does, but unplugging the small harness to it is required to get isolation between the main ground and main positive.
The final piece is on the port side of the engine and is what I believe to be my high RPM fuel pump (Seems this engine has a low & high RPM pump?) It has a red wire that comes straight from the main battery post. It has a slightly smaller red wire with a blue stripe that (I think) terminates into the lower of the two computer harnesses. Disconnecting the Red/Blue wire -OR- Disconnecting the harness to the lower computer module terminates this loop. From what I've read, the fuel pump is ground-switched and with the ignition in the "off" position, the ground wire should be disconnected, but it's not.
So, to get complete isolation of the positive/ground, I disconnect the heavy guage red wire from the alternator/rectifier. I unplug the sensor on the starboard side/front/lower corner of the engine. I disconnect the red/blue wire from the high RPM fuel pump.
Note that the sensor AND the alternator give SOME impedence, though it's only a few ohms. The fuel pump gives no impedence at all.
Do I have a bad computer module? Are there relays under that cover?
Master of the Mercury, I know you must be out there! Help!
I have a Merc 225 EFI, 3.0 Litre outboard. Serial number begins with 0G28. Unfortunately, I can't find a model number. I know it's supposed to be on a silver plate on the mounting bracket, but either it's gone or I'm daft... probably the latter of the two.
The old battery was absolutely shot, old and dead and was not disconnected when the boat was put into storage.
Installed a brand new battery and noted that I got some spark when connecting the terminals.
I turned the engine over just to make sure it would crank. No ears on, so I didn't attempt to start it.
Everything was left turned off and key out of the ignition and it drained a brand new battery in less than 18 hours.
With ignition and all accessories "off" and battery disconnected, I put an ohm meter to the two heavy gauge wires running to the engine. The result is almost no impedence (short circuit?)
I pulled the elecrical cover on the starboard side of the engine to reveal the starter relay, etc. The main positive connects to the bottom side of the starter relay, along with 5 other wires. I pulled this loose and tested the individual wires for short circuit. I got no impedence on a medium guage red wire that runs directly to the alternator. Also got no impedence on one other wire. I was unable to trace it with absolute certainty, but I believe it went to the power trim system.
In short (don't mind the pun) - I think this is probably a bad rectifier. But for the life of me, I can't find the thing!! Can someone please confirm if my suspicions are likely correct? If so, where is the rectifier? (Pictures and/or detailed instructions would be greatly appreciated. Once I have located and isolated the rectifier, how do I test it?
************************************
UNDER THE COWL:
I thought a description of what's under the cowl might help ID the engine. If that's not necessary, please ignore this entire section.
There are two EFI computer modules, one above the other, on the rear of the engine. 3 Coil pack and three plugs on the left and 3 coil packs and plugs on the right. There's an electrical compartment with cover held by 3 screws on the starboard side. Underneath is a starter relay, what appear to be 2 other relays (possibly power trim?) The small cover for that compartment has a single blade fuse on the outside.
The alternator is mounted on the top of the engine, toward the rear. There is one medium guage red wire with a boot and a small plug of some sort with 2 wires coming out (one is purple.)
The front of the engine is a solid aluminim plate held on by some large allen-head screws.
************************************
Thank you in advance for any assistance!
UPDATE!
Ok, so it seems the rectifier is built into the alternator. If I ground the (-) side of my ohm meter to the power head and place the (+) terminal to the copper bolt sticking out of the alternator, I get a reading with a small amount of resistance. If I switch the terminals and place the (+) side of the ohm meter on the block with the (-) probe on the copper bolt, I get no reading (infinite resistance.) To the best of my understanding, this is correct in that the diodes of the rectifier are working properly and only allowing power to flow in one direction, turning the AC current into DC current.
So... not the rectifier/alternator? However, it seems that with the ignition in the off position, there should be some sort of relay that prevents this flow of power so as not to drain the battery. I'm a bit stumped here, but I moved on.
There is some sort of small sensor/device on the Starboard side of the carb. housing that has 4 leads plugged into it. This device also seems to be allowing power to flow from positive to negative when plugged in. I have no idea what it is/does, but unplugging the small harness to it is required to get isolation between the main ground and main positive.
The final piece is on the port side of the engine and is what I believe to be my high RPM fuel pump (Seems this engine has a low & high RPM pump?) It has a red wire that comes straight from the main battery post. It has a slightly smaller red wire with a blue stripe that (I think) terminates into the lower of the two computer harnesses. Disconnecting the Red/Blue wire -OR- Disconnecting the harness to the lower computer module terminates this loop. From what I've read, the fuel pump is ground-switched and with the ignition in the "off" position, the ground wire should be disconnected, but it's not.
So, to get complete isolation of the positive/ground, I disconnect the heavy guage red wire from the alternator/rectifier. I unplug the sensor on the starboard side/front/lower corner of the engine. I disconnect the red/blue wire from the high RPM fuel pump.
Note that the sensor AND the alternator give SOME impedence, though it's only a few ohms. The fuel pump gives no impedence at all.
Do I have a bad computer module? Are there relays under that cover?
Master of the Mercury, I know you must be out there! Help!
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