85' Mercury 115 only firing 3 cylinders

[coreyw20]

Hey everyone,
New to the forum here and have already found lots of good info on here.

My problem is I have a 85' Mercury 115 l6 outboard that I am only getting fire from 3 cylinders. The serial # for the motor is OA154753. The cylinders that are missing are 1,3 and 6. I have tested the Stator and Trigger.

Stator test results: bl/wh & red/wh = 5.5 ohms
red & ground = 138
red/wh & ground = 138

The Stator seems to have passed the test, but I could only get 8 ohms through all tests of the trigger. I also tested the Rectifier. It is completly gone. Could the rectifier cause some cylinders not to fire, or would the trigger barely failing the ohm test cause it? Any suggestions?

P.S. - I also replaced the coils with new ones just to make sure it wasn't them causing it. Same result only three cylinders firing.

 

[CharlieB]

Re: 85' Mercury 115 only firing 3 cylinders

85, are you sure it isn't 1, 3, and 5 missing and not 6?

If I remember correctly, you ignition has two switch boxes, one for even cyl and one for odd cyl's. A bad Bias circuit in the evenbox can cause the odd box not to fire. Disconnect the Bias wire from the odd box and test for spark.

WARNING: Do NOT attempt to start themotor, timing will be way off and can cause extensive damage with the Bias disconnected.

If you have spark now on all 6 then replace the even switchbox.

Note: Factory and CDI Electronic both highly recommend replacing 's BOTH boxes when the Bias fails one even just one box.

If the above test fails to determine your problem then before ordering ANY non-returnable electric parts, download the free Outboard Ignition Troubleshooting Manual from CDI Electrics.com It very clearly leads you thru complete dianostics to determine your problem.

 

[coreyw20]

Re: 85' Mercury 115 only firing 3 cylinders

Just double checked. and it is the #1, #3, and #6 cylinders that are not firing. Which wire is the bias wire. I am going to disconnect the bias wire and try you suggestion. Is there anyway to test a switch box?

 

[CharlieB]

Re: 85' Mercury 115 only firing 3 cylinders

The Bias wire is White, short, in the top left corner, linking the two boxes together. Disconnect from both boxes and recheck for spark.

Unfortunately, there is no bench test for the switchboxes, it is a process of elimination, testing the stator, trigger, and kill wire for problems, once each is proved good then the only thing left is the box. Which is why you must follow the directions lined out in the Troubleshooting Guide TO THE LETTER.

Some of these parts can get expensive, and there is NO RETURN on electrical parts!!!!!

Download the free Troubleshooting Guide, read it twice, get a DVA Meter and test, retest again to PROVE your results.

Post your results here, we will confirm or point out anything else that could contribute to your problem. This way you can be quite sure you will not be spending money on unnecessary parts.

 

[coreyw20]

Re: 85' Mercury 115 only firing 3 cylinders

O.k. Downloaded the C.D.I. troubleshooting guide. Went through it and got the following results.

Stator meter set to .1k: Blue to ground = 40
Bl/wh to ground = 55

meter set to x10: Red to ground = 10
red/wh to ground = 10

Trigger meter set to x10: brown to white = 120
white to purple = 120
purple to brown = 120

I take it if I multiply my findings by the meter setting then both of them pass.

I have also replaced the rectifier.

I retested each cylinder for spark and now I only have a spark on 2 and 5.

I am going to switch the wires around on the switch box's next. I just want to be sure I know what wires to switch. I assume I just swap out the red and red/white on one box and put them on the other switch box where the blue and blue/white wires are and vise verse. Is there any other way to test for voltage at the switch box's without a DVA adapter? Also how can I tell what charging system I have?

Thanks

 

[CharlieB]

Re: 85' Mercury 115 only firing 3 cylinders

Before you go to the trouble of swapping stator leads, first check and charge your battery fully. This system needs a MINIMUM 300 RPM cranking speed to generate enough electricity to fully operate and fire all cyl's.

At first glance it appears that the readings for your stator and triggers are good, however, Ohm's readings are not perfect at detecting a broken winding which CAN read Ohm's yet fail to generate once put to work. The DVA is the most reliable indicator.

A bad rectifier can cause intermittant spark or no spark on some cyl's, the magnetic field of the charging coils infringes on the magnetic field of the ignition. Changing the rectifier should have cured that, however if the battery is already ran low on charge you may be just nearing the minimum cranking speed and the system cannot function reliably.

Easy test to charge the battery then retest spark.

Then, if still no spark swap the stator leads to see if the problem switches to the other box. Be sure to return all wires to their correct location BEFORE starting the motor, it does make a difference in timing and can cause damage if left switched.

Did you try the Bias wire test as spelled out in the Troubleshooting Guide?