1995 Mercury 115 running rough

[JML1001]

Hi All, I am trying to fix an ignition issue on my 1995 Mercury 115 (SN: 0G199179). As some background, I had a broken plug wire on the bottom cylinder which I believe lead to my voltage regulator going out. Voltage regulator, all plug wires and the bottom cylinder ignition coil have all been replaced but it runs rough now and trying to track down the issue.

I am following the manual test procedures starting with checking my ignition coils. Manual states to put the red DVA lead on coil + and black DVA lead on coil -. I did my test to start off with at idle, about 800 RPMs. When I do this the readings are about 190 on the top cylinder, 130 on the next one, 50 on the next one and no reading on the bottom. So only one reading in spec of 150-250V. As I increase RPM's, readings go up but still have the same difference between cylinders.

If I do the same test with red DVA lead on coil + except put the black DVA lead on the bolt on the switchbox where all the negative coil wires run to I get a consistent 220 across all cylinders at 800 RPMs, so reading within spec.

Coils have all been checked and resistance readings are within spec. All other voltage and resistance checks per manual of the stator and trigger are within spec across all RPM ranges as well.

Looking for some input as ignition parts are pricey and I hate to just throw parts at something hoping it will fix it.

Thanks

 

[JML1001]

Also forgot to mention that battery voltage never goes above 14 volts even at wide open throttle. Battery is 1 year old and has been load tested and was strong.

 

[Texasmark]

I had a 2002 90 which had separate CDI modules.....triggers in, 12 v from battery, ground, and trigger kill; spark plug wire out. I don't have a switch box. See if I can shed some light anyway. Some brainstorming:

Get an automotive timing light and clip it onto each of your spark plug wires at 1000-1500 rpm. What do you see?

Did you have the rough running prior to changing the coil in the switch box?

If #4 is erratic or shows some other abnormality, swap coils with another cylinder and see if the problem follows the coil. Come back. If you can swap more of the #4 trigger components with another cylinder do that too.

The regulator is a different set of stator coils and has no bearing on the triggers other than voltage supplied to the switch box that is used to charge the storage capacitors therein which produce the energy to fire the plug.....low voltage, low power, misfired plug.

If you have a red stator, you should have 16 amps available from your regulator. If you are using a lot of that you could expect your voltage to be maxed out at 14V at WOT. Question is, what's sucking the juice.

Normally your plug will light off somewhere around 10-12 kv. With the Merc 40kv ignition, if not loaded with a plug gap, and it's working per spec, your ignition circuit could experience the full voltage which would be reflected as a maximum voltage (which is never seen under normal operating conditions, back through your trigger ckt for that cylinder and could blow out some other components, the coil that you changed, or the charging capacitor for that cylinder or a smaller diode or microchip if any. If you can swap out a complete module (trigger input to output hv coil) do it and check the performance on that cylinder.