1995 Mercury 200 XRi, serial # OG178803
I apologize in advance for the lengthy email but I wanted to clearly document my noted issues and all troubleshooting what I’ve done in the hope someone can help me finalize the root cause.
Had the boat out 2 weeks ago and it ran fine all morning. I stopped to fish after a short run, fished for maybe 20 mins, and cranked the boat up with no problem. Was idling out of a shallow bay and all of a sudden the motor died like someone pulled the kill switch.
I checked the kill switch at the throttle and it was fine, so I trolled home put it on the trailer and took it to the house.
Started with the basics and found that I had zero fuel pressure. Used the service manual troubleshooting guide to narrow the problem down to a bad fuel pressure regulator (stuck open). Replaced the pressure regulator, found that I now had 32 PSI, boat fired right up and ran great on muffs. All was good, so I thought.
I took the boat out the next day and it ran fine all morning. Again, I fished a while and then I went to start it and noticed it was a little hard to start. Usually the motor fires on the first turn but it took a while to start. Ran back toward the ramp and decided to fish one last spot before going home. Fished for maybe 30 mins and then she wouldn't start. Turns over just fine but won't fire. Trailered it home and did more troubleshooting.
I found that I still had good fuel pressure (32 PSI) prior to start, so didn't believe that to be the issue this time. Grabbed my DMM and checked the kill circuits on the switchboxes and both of those were OPEN if the key was on, as expected. I then grabbed my inline spark tester and found that I had no spark on all 3 cylinders on the starboard side. Port side 3 cylinders were fine.
Put it in the garage and did some research online and in the service manual. From what I read, it was likely either a stator or a switchbox since it was all 3 cylinders and an easy test was to swap the RED/BLUE and RED-WHITE/BLUE-WHITE wires to see if it had same issue (no change; indicating a switch box problem) or changed sides (stator problem). My plan was to perform this test 1st thing the next a.m. As a basic check, went ahead and took some readings that were spec'd in the service manual for the stator:
Resistance between RED/BLUE: 3722 Ohms (within spec)
Resistance between RED-WHITE/BLUE-WHITE: 3838 Ohms (within spec)
Resistance between RED/BLACK: 108.8 Ohms (within spec)
Resistance between RED/WHITE/BLACK: 107.9 Ohms (within spec)
Resistance between BLACK-YELLOW/BLACK: OPEN on both switch boxes (within spec)
Next morning - pulled the boat out and put it on muffs. Before swapping the stator leads on the switchboxes I wanted to confirm the problem as a baseline. Turned the key and it fired right up! Went ahead and checked fuel pressure:
@ START: 32 PSI
@ 1000 RPM: 34 PSI
@ 1800 RPM: 34 PSI
@ 2500 RPM: 34 PSI
@ OFF, 20 mins after shutoff: 28 PSI (Bulb still firm)
I couldn't duplicate the problem for an hour or so and finally shut it down to let it sit. Did this for maybe 30 mins, went back out, and fired it up again. It ran for about 45 seconds and then died. Fuel pressure still read 32 PSI and again had no spark on starboard side. I again confirmed all resistances as listed above and they came back almost identical.
I decided to go ahead and switch the RED/BLUE and RED-WHITE/BLUE-WHITE wires to try to duplicate the problem again to see if it followed the switch box. Before doing anything, I rechecked the resistances and they were different but similar:
Resistance between RED/BLUE: 4022 Ohms (within spec)
Resistance between RED-WHITE/BLUE-WHITE: 4029 Ohms (within spec)
Resistance between RED/BLACK: 116.5 Ohms (within spec)
Resistance between RED/WHITE/BLACK: 115.4 Ohms (within spec)
Resistance between BLACK-YELLOW/BLACK: OPEN on both switch boxes (within spec)
Repeated the spark test and still had no spark on the starboard side.
I'm assuming this means my switch box is bad? Visual check of the stator coils looks OK (to this untrained eye) and the bullet connectors all look good. Voltage regulators were both replaced about 2 years ago and I see 14.3 VDC max as expected.
Re-read the service manual and found the test about the bias and kill circuits. Performed the following:
1. Removed the bias circuit (WHITE-BLACK) from the outer switchbox - still no spark on all 3 starboard cylinders
2. Removed the kill circuits (BLACK-YELLOW) to both switchboxes - still no spark on all 3 starboard cylinders
3. Tested the bias circuit resistance relative to switchbox case ground with WHITE-BLACK wire removed - outer box, which controls the starboard side, shows 14.1 kOhm. The manual says it should be 1300 - 1500 Ohm so I'm assuming this is bad. Not surprising since I have no fire on that side.
4. As a reference, decided to also test the inner box by measuring resistance between the WHITE-BLACK wire connector (still connected to inner box) and case ground - also shows 14.1 kOhm. In looking closer and repeating the test, I found that the WHITE-BLACK wire looks to have burnt bullet connector.
Could this be my issue? Bad bias circuit on both switchboxes even though the inner is still provided spark to the port side? I'm guessing the Merc service manual is correct and it truly should be 1300 - 1500 Ohms and not 13kOhm - 15kOhm, but can someone please confirm?
Should I replace both switchboxes?
Any and all input is much appreciated!
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Originally Posted by skeeter91
