175 Mariner fell on its face all of a sudden

[Jmr1974]

Had the boat out yesterday doing some skiing. When we finished up my boys wanted to take one more fast lap around the lake when all of a sudden it was like I let off the pedal and the boat came to a stop. The motor started right back up but would not get back on plane. When trying to plane off it gets to a certain rpm and that’s it, I would say somewhere between 1500-2000rpms. What’s strange is it starts right up and idles just fine. I had to drive it this way to get back to the launch which was probably a half mile or so drive and it never skipped a beat. I tried a few more times on the slow ride back to plane off but nothing changed. Today I pulled the plugs to see what they looked like and the seemed fine. After looking around a bit more I noticed some wiring has been chewed on. Here’s some pics.Attachment 472211Attachment 472213Attachment 472214Attachment 472215 You can see where the wire is exposed on the underside of the advance module, then the purple wire is also exposed that goes to the other module on the side of the engine, then the insulation is split on the two yellow wires that go up under the flywheel. Could this be my issue with the motor? I was going to do a compression test when I noticed these exposed wires. I have no clue when it comes to wiring but exposed wires turning green can’t be good. Motor is a 1985 175hp Mariner about as clean as they get for its age. Ticks me off mice somehow got to it while being in my garage Under a cover with 4 garage cats to protect it from mice! Crossing my fingers you guys in the know will tell me this is an easy fix....

[Merc 2.5]

Stator or switch boxes probably. Unless it ran hot. Need do a spark check , just make sure they all firing

[SS Minnow]

If you have exposed/chewed on wiring that would be the first place I would be looking. Your pictures did not upload to here, at least I cannot see them.

[nitro_rat]

Yeah, I would look everything over real good first. Download the free troubleshooting guide from cdielectronics.com. Likely the high side of your stator took a dump. May need a DVA adapter for your multimeter to complete troubleshooting, a cheap one from ebay works well...

[Jmr1974]

I don’t know why the pics never showed up but here they are.

[Merc 2.5]

Ya those ain't chewed on. Thats the result of charging /stator wires over the years. Its normal. But will need to replace regulators and stator. Mite have couple trigger wires like that to.

[Jmr1974]

Ya those ain't chewed on. Thats the result of charging /stator wires over the years. Its normal. But will need to replace regulators and stator. Mite have couple trigger wires like that to.

When you say regulator are you calling the box that says advance module on it? There’s one on top of the motor right behind the flywheel and one on the side of the motor, they both look the same but only the one on the top has that advance module and part# on it. Both have a bare wire, top has bare red wire and side has bare purple wire.

[rgsauger]

And plan on tossing the black boxes, too. Seriously, they cause nothing but problems

[Jmr1974]

And plan on tossing the black boxes, too. Seriously, they cause nothing but problems

So your saying I can completely remove both boxes and the motor will still run? In other words the motor never needed them in the first place... I’m not sure they even make the boxes anymore.

[Soporific]

Did you get your motor fixed? Your symptoms were like mine and ended up being the hub magnet in the flywheel. The only way I found it was putting a scope on the trigger output pairs to see the voltage pattern. Scopes are cheap on ebay, $30 and a computer or smartphone too. Good luck and I hope you get it fixed.

[Jmr1974]

Did you get your motor fixed? Your symptoms were like mine and ended up being the hub magnet in the flywheel. The only way I found it was putting a scope on the trigger output pairs to see the voltage pattern. Scopes are cheap on ebay, $30 and a computer or smartphone too. Good luck and I hope you get it fixed.

I haven’t had a chance to do much to it. I did do a compression test this morning, all cylinders are at about 128-130lbs this is ice cold I did not warm the motor up before testing. I then checked for spark, all cylinders had spark except cylinder #3, nothing at all on #3....

[Soporific]

Still could be a lot of different things. No spark on #3. A DVA is handy as already mentioned, but without one, you could switch coils and see if the problem follows. Switch the switch boxes and see if the problem follows. Change the spark plug. Do you have a timing light, if so, index the flywheel to see that the cylinders are firing in order correctly. 1,2,3,4,5,6 and at the right timing mark. Check the pairs of trigger wires to get 1100 to 1400 ohms on each of the three pairs with a DVM. Disconnect the bias white wire on the top of the switch boxes and note any changes at idle etc. to get started. Keep posting your results. Compression is good.

[Jmr1974]

So what do these two boxes do exactly? I ask because a few posts up a member says to toss them out, would either of them have anything to do with my problem? Would either of them cause cylinder #3 to not have spark? The box on the side Of the motor has a purple wire coming out of it that is missing insulation that you can see in the pic. The box On top has a red wire coming out of it that’s missing insulation and has that corroded look like it’s been like that for a while, the purple wire from the side box that is exposed is nice and shiny copper like it just happened not long ago. Also What do the wires do that my pinky finger is pointing at? Theses wires come out of the side box and go on top of where the gear goes for the oil injection, I removed all oil injection stuff last summer and premix. I need to get a DVA adapter for my multimeter and figure out how to test the stator and trigger. Meanwhile please help me understand what these two boxes do.

[Soporific]

Maybe download a mercury service manual for your motor and follow the testing procedures. Lots of good advice given already and you can make your own DVA adapter if you want. CDI site has good trouble shooting downloads as well. Good luck and keep going. I am not convinced that the boxes have failed but many here with much experience recommend to discard them to limit your future problems with this motor. Welcome to electrical problems.

[Soporific]

No spark on only one cylinder seems to point to a switch box failure, but randomly testing things is not efficient and sometimes not helpful. Try to follow proven procedures and you will succeed with all the knowledge and help here.