1994 Merc 115 Fires but wont start

[SidMich]

1. Put motor on my boat. Low hours motor in very good condition. Plugged in harness and attempted to hook up tach. Test start on the muffs. Motor started briefly, then blew the fuse under the hood.
2. Replaced fuse, disconnected all wires except basic harness connections. Motor started right up appeared to run fine.
3. Put boat in the water, motored about 5 min at low RPM (approx. 800-1200) out to channel. Brought boat up on plane, probably around 3500-4000 RPM. Ran great for about 1/4 mile, then stopped cold. No alarms, just stopped. Restart attempt would immediately pop for a second, then nothing. Fuel was my first thought. Checked it out, seemed ok. Seemed like motor would immediately pop as if starting, then when I got off the start switch and went back to the 'run" position, it would immediately stop.
4. When I got home, I did some standard tests: cleaned plugs, alternate fuel source, etc. Nothing doing. Same deal, pops instantly, then instant die when I get off the start switch and return to "run" position.

Based on what I'm experiencing, I'm guessing the ignition switch may be failing for some reason???

Would the kill circut behave this way for some reason?

I searched the archives and didn't seem to home in on anything. Some sounded a little similar, but nothing real close.
Any advise appreciated.

 

[Plainsman]

Re: 1994 Merc 115 Fires but wont start

Have you found the problem? If so, please share.

 

[SidMich]

Re: 1994 Merc 115 Fires but wont start

1. Put motor on my boat. Low hours motor in very good condition. Plugged in harness and attempted to hook up tach. Test start on the muffs. Motor started briefly, then blew the fuse under the hood.
2. Replaced fuse, disconnected all wires except basic harness connections. Motor started right up appeared to run fine.
3. Put boat in the water, motored about 5 min at low RPM (approx. 800-1200) out to channel. Brought boat up on plane, probably around 3500-4000 RPM. Ran great for about 1/4 mile, then stopped cold. No alarms, just stopped. Restart attempt would immediately pop for a second, then nothing. Fuel was my first thought. Checked it out, seemed ok. Seemed like motor would immediately pop as if starting, then when I got off the start switch and went back to the 'run" position, it would immediately stop.
4. When I got home, I did some standard tests: cleaned plugs, alternate fuel source, etc. Nothing doing. Same deal, pops instantly, then instant die when I get off the start switch and return to "run" position.

Based on what I'm experiencing, I'm guessing the ignition switch may be failing for some reason???

Would the kill circut behave this way for some reason?

I searched the archives and didn't seem to home in on anything. Some sounded a little similar, but nothing real close.
Any advise appreciated.

 

[SidMich]

Re: 1994 Merc 115 Fires but wont start

Been out of town for a week. Was hoping to get some feedback while away. Nothing.
I'll be taking a look at it this week and will post if I figure anything out.

 

[emckelvy]

Re: 1994 Merc 115 Fires but wont start

One thought, if you left the key in the 'start' position for just a little bit longer, would the motor continue to run? If so, I'd expect there's a problem with the key switch. This may have even been the reason for blowing the fuse. BTW, the ign ckt is self-powered so the fuse incident should have had nothing to do with spark problems.

One other thought, you can disable the ign kill circuit (which grounds out the CDI box to kill spark) by pulling the kill wire off the CDI box. If I recall it's the black wire with yellow stripe but might be white stripe. You'll need to check your manual to be sure.

Another very common problem with many big Mercs in this year range is bad stator windings. Disconnect the blue & red wires and also the blue/wht and red/wht wires going to the CDI box and measure the resistance of these wire pairs.

If the resistance readings don't match those of your manual, the stator is shot and must be replaced. If you find your spark problem is caused by a bad stator, check www.boatfix.com for pretty good deals on an aftermarket CDI brand replacement.

Cheers and hoping this helps guide you to a solution..........ed

 

[SidMich]

Re: 1994 Merc 115 Fires but wont start

I pulled the switch off tonight and did some basic resistance testing with my meter. All the behaviors I'd expect of a functioning switch were present. With one lead on the "B" post (battery), I connected the other lead to the "I", "S" and "C" posts. In each case, the resistance went to essentially zero when I engaged the respective functions on the switch. (I.e., "on" position, start position and start+choke). So, it would appear that the switch is at least behaving as expected with no load on it.

Anybody know if that is common behavior for a "bad" switch?
More tests to come...

 

[gungalunge]

Re: 1994 Merc 115 Fires but wont start

mitch i too just had some weird stuff going on here on my 5th time out with my rebuild . acting like it is fuel related . I refueled my tank and mixed the oil and gas .i took off great until 5 minutes later . she slowly lost power . and died . the whole thing is it ran great until i refueled and took it out the next day .things happen but until i diagnose the problem I am sitting her banging my head . I was towed in tonight .:/. I was testing the reliyability and saying to myself .now it is time to trust this thing .now i am swallowing a lot of my faith .. I hope like you that it will not be an expensive repair . I will give it a go tomarrow .

 

[andy6374]

Re: 1994 Merc 115 Fires but wont start

without testing the key switch explicitly...bypass it to see if you can get the engine running. Unhook the wiring harness at the engine and remove the blk/yel wire at the switchboxes. Jump the starting solenoid and see if it continues to run. Note that if it does start you wont be able to kill it, instead just manually choke the engine until its dies.

However, if I had to put money on it I'd say it just a ailing kill switch (blk/yel wires) or lack of fuel. Spray a premix into the carb throats and see if it runs.

Good luck

 

[alana]

Re: 1994 Merc 115 Fires but wont start

could be wires inside remote throttle/gear control traped and warn through by moving parts

 

[SidMich]

Re: 1994 Merc 115 Fires but wont start

Spent the afternoon fidling with the problem. Some preliminary probing with the volt/ohm meter seemed to indicate things should be ok. Tried to fire it up w/ same result as before.

emcelvy, the suggestion to try holding in the start position may have been the ticket. That sounded a little shaky, as in I thought it might damage the starter. I tried it with the hood off and could see that the starter disengages once the engine fires. It started and continued running.

From that point, I continued messing with the switch and switch connections and got various behaviors, including working normally. Looks like it's the switch.

I will confirm once replaced.

 

[emckelvy]

Re: 1994 Merc 115 Fires but wont start

Definitely replace the switch, it sounds gunnysack. One word of caution with bad ign switch, if it sends 12V back thru the kill wire ckt because the switch contacts are messed up, it could damage the CDI unit.

These black boxes don't like 12V applied!!! You can check for voltage to ground on the kill wires to see if the switch has been misbehaving in that manner.

Sounds like you're on the right track, glad it helped......ed

 

[Laddies]

Re: 1994 Merc 115 Fires but wont start

If you disconnect the blk/yellow wire at the switchbox as Andy told you in his post, it will tell you if the problem is in the ign or the boat wiring (switch and etc) then as he said if it if you have fire, squirt it with fuel and that will tell you if it,s fuel a related problem. Sorry for your lack of real help, but this board seems to be taken over by the padders, guessers and computer literate, most real mechanics simply don't have the time to wade thru the BS to see who has been helped and who has not. I have not posted much myself and have noticed lack of posts from other mechanics lately, thought that is was time to open this can of worms and not trying to steal your thread but some responses lately are embarassing.- Bob

 

[Boatwizard]

Re: 1994 Merc 115 Fires but wont start

Laddies probably has the right cause, the kill circuit.
If that doesn't fix it, try checking the flywheel key, it may have stripped if someone didn't tighten the flywheel properly.

 

[alana]

Re: 1994 Merc 115 Fires but wont start

If you disconnect the blk/yellow wire at the switchbox as Andy told you in his post, it will tell you if the problem is in the ign or the boat wiring (switch and etc) then as he said if it if you have fire, squirt it with fuel and that will tell you if it,s fuel a related problem. Sorry for your lack of real help, but this board seems to be taken over by the padders, guessers and computer literate, most real mechanics simply don't have the time to wade thru the BS to see who has been helped and who has not. I have not posted much myself and have noticed lack of posts from other mechanics lately, thought that is was time to open this can of worms and not trying to steal your thread but some responses lately are embarassing.- Bob

 

[alana]

Re: 1994 Merc 115 Fires but wont start

i might be a padder and guesser but it took the local agents of my motor 7 weeks to identify and replace a blocked fuel injector so dont tell me all experts are gods