85 Mercury 115 Ignition problem

[crankbait]

Hello,<br />Long time lurker, but I finally have the need to post! I have an 85 Mercury 115 HP inline 6 that is having an ignition problem. It wont start because I only have spark on 1 of the 6 cylinders when cranking. On ocassion it will fire up and once running, she will run rough for a while, then she will eventuall wake up and scream accross the water like nothing is wrong. Since it eventually runs very well, this leads me to believe it's not the switchboxes. Also, switching the place f the two switch boxes does not move the problem. I popped the flywheel and the stator looks almost new. So it's either the trigger or stator, I think. I know it sounds strange, but could the trigger or stator be failing on 5 out of the 6 cylinders only when cranking, or does it seem like an electrical problem? To be honest, I am not sure I even understand what the trigger does. Your help is much appreciated. I tried everything I could before posting. Thanks!

 

[crankbait]

Re: 85 Mercury 115 Ignition problem

bump

 

[Cutbait]

Re: 85 Mercury 115 Ignition problem

I had a similar problem with my '82 Mercury 50 hp. It was hard to start and when it did, it would have no power at first. Then , like yours, it would wake up and run fine. After much trial and error, I replaced the switchbox. That cured the problem. May do the same for yours.<br /><br />As I understand it, the trigger detects the position of the crankshaft ( and thus the position of the pistons) and reports it to the switchbox. It tells the switchbox exactly when to send the spark to the appropriate cylinder.<br /><br />Hope this helps.<br /><br />Cutbait

 

[Dennis4b]

Re: 85 Mercury 115 Ignition problem

Cutbait is right, there are pickup coils in the stator which will send a small sine wave pulse to the switchbox whenever a certain cylinder needs to be fired. <br /><br />If you have access to a scope, but possible a DVA will do, you can see the pulses easily. For every switchbox wire going to a coil (they're greenish I think), there's a wire next to it that goes to the stator, there's your triggers. <br /><br />These work through a magnetic pickup, and it is highly unlikely they would be affected during cranking and not when running. <br /><br />If I remember correctly the stator will also provide the high voltages the switchbox uses to charge it capacitor(s) to send juice to the coils at the right time.<br /><br />Try to determine wether all trigger signals are arriving at the switchboxes. Then use a DVA (scope is probably too slow to pick up) to see if pulses are sent to the coils. <br /><br />I don't know enough to give you more help, but searching groups.google.com with something like "mercury ignition problems" will give you plenty of reading ) Goodluck!

 

[12Footer]

Re: 85 Mercury 115 Ignition problem

I just love intermittant problems. My father used to call them Gremlins.<br />But an intermittant connection can cause this symptom. I'm not saying the switchbox or a coil hasn't laid down and died, but they're very expensive to swap-test ( the only method without the Merc diagnostic meters). So make absolutely sure all the connections of everything "ignition" is shiny clean, by undoing them one at a time, cleaning them shiny,and re-assembling.<br />If that cures it, you aren't done. You must coat these connections to waterproof them.<br />One other trick that has found many a gremlin loose in the ignition...Run it with the cover off on a dark night,and look for arcing. Those places it is found will short the HV to ground instead of at the plug gap. Not only that, but it can damage coils, plug wires and switchbox.

 

[crankbait]

Re: 85 Mercury 115 Ignition problem

Thanks Everyone! I kneew I'd get some help! I will crank it in the dark to see what I can find. The neighbors will love me! I have verified that it's not the coils... I did this the expensive way. 6 new coils, $150, a tank full of gas and 12 pack of beer, $25... an outboard that still doesn't run... worthless.

 

[crankbait]

Re: 85 Mercury 115 Ignition problem

I fixed it!! Just so people searching know... it was the switch box. Seems like 90 Percent of the ignition problems with these old Mercs is the switchbox. Ran like a top as soon as I installed the new box. Got her up to 63 mphtoday. So all is definitely well. I am happy. Thanks to everyone for your help.