Mercury Tech Help Needed

[flounderpounder225]

Shipmates,
Grew up on OMC, and Yamis for the last ten years, so need some advice.

1989-90 ish Merc 90 HP 3-Cyl. no apparent spark while cranking.  What is the test-light procedure to see where We are losing it.  I see the power pack and and mag-amps where the plug wires connect to, is there a quick way to test the secondary ignition to ID the bad part? Thinking stator, but would like to be a little more sure before buying parts
Thanks
Marc

[seabob4]

Marc,
I know it sounds simple, but how do we shut down motors?  Ground the coil, or, in an O/Bs case, the coils.  Think about when you pull the kill switch lanyard.  What happens?  Sends a ground to the coils, motor shuts down.  Keep the the lanyard pulled, you can crank to kingdom come, the motor will never turn over...

A place to start, you know...I have had Mercs that wouldn't shut off when you turned the key, the ground wire in the engine harness was broken somewhere, wired a lead from the batt -, touched a coil (they are all jumpered together), viola, motor shuts off.

Keep in mind, Mercs, Yams, OMCs, they're all engines, they all pretty much work the same way...

[fitz73222]

Hi Marc,
Do you know the history of this motor? If someone reversed the battery cables, plan on a new switchbox (CDI module). If thats not the case, here are some things to do. You are going to need a DVOM (digital volt ohms meter). First check; isolate the harness and keyswitch by unplugging the harness on the engine. It is located adjacent to the cowl mounted trim switch inside the cowling pan. With a fully charged battery jump the starter solenoid and crank the engine, check an see if the spark comes back. If it does look at replacing the key switch. Since this motor has individual ignition coils we can pretty much rule out the coils as root cause for all the cylinders to not have spark. Next is the stator and trigger. You cannot test the ignition side of the stator at home. It needs to be tested with a voltage inductive Mercury service meter at the dealership. The trigger can be tested with your DVOM. The trigger is the component that rotates via the timing arm as you advance the throttle. Locate the wiring from the trigger to the switchbox. you may have to remove a cover plate to gain access to the switch box connections. Should be Brown, white/black,white, and violet. Set the DVOM to RX100. Test leads connected to brown and white/black 1100-1400 ohms. White to white/black 1100-1400 ohms. Violet to white/black 1100-1400 ohms. If any readings out of range replace the trigger. You cannot remove the flywheel with a regular puller. you will need a special flywheel puller for Mercs that you should be able to borrow. Do these tests and post results.

[flounderpounder225]

Hi Marc,
Do you know the history of this motor? If someone reversed the battery cables, plan on a new switchbox (CDI module). If thats not the case, here are some things to do. You are going to need a DVOM (digital volt ohms meter). First check; isolate the harness and keyswitch by unplugging the harness on the engine. It is located adjacent to the cowl mounted trim switch inside the cowling pan. With a fully charged battery jump the starter solenoid and crank the engine, check an see if the spark comes back. If it does look at replacing the key switch. Since this motor has individual ignition coils we can pretty much rule out the coils as root cause for all the cylinders to not have spark. Next is the stator and trigger. You cannot test the ignition side of the stator at home. It needs to be tested with a voltage inductive Mercury service meter at the dealership. The trigger can be tested with your DVOM. The trigger is the component that rotates via the timing arm as you advance the throttle. Locate the wiring from the trigger to the switchbox. you may have to remove a cover plate to gain access to the switch box connections. Should be Brown, white/black,white, and violet. Set the DVOM to RX100. Test leads connected to brown and white/black 1100-1400 ohms. White to white/black 1100-1400 ohms. Violet to white/black 1100-1400 ohms. If any readings out of range replace the trigger. You cannot remove the flywheel with a regular puller. you will need a special flywheel puller for Mercs that you should be able to borrow. Do these tests and post results.

Thanks all, I have the DVOM, just knowing which colors to run the resistance check on will help greatly, and I have the puller for the flywheel, so cheap these days ($20) its not worth not having one.  Is the Black/yellow the gound to shut the engine down?? It goes to some type of small device screwed into the side of the engine?  Maybe a tilt sensor that won't allow the engine to start if tilted too high?  Just a guess

Marc

[fitz73222]

Black and yellow is the traditional kill wire. That used to run to a mercury switch to keep it from cranking when tilted up. That should be simple to run a continuity test if it still used one or just disconnect it and/ or jump the circut. I've got factory service manuals for 94' and 98' but the trigger lead colors are the same so I'm assuming the colors are the same for earlier models. Keep me posted, I have generic service manuals for other years if the trigger wire colors are different.

[fitz73222]

One other crazy notation. Don't do the resistance test in the heat of the day in direct sunlight unless you can get the motor in the shade and somewhat cooler. The test is designed at room temp. The factory manual recommends this because the outside temp can affect the resistance readings.

[flounderpounder225]

Bob / Fitz,
Trigger assembly.  2500 Ohms between test points, already have it removed and researching availability and price.  (PN 99021A3) Thanks again
Marc

[fitz73222]

Excellent!

The least expensive of all it could have been...

[flounderpounder225]

Excellent!

The least expensive of all it could have been...

Except to unplug the "Mercury Switch"     Honestly I think the trigger was still bad, I read it sitting on the bench and she was 2500 Ohms, so if it wasn't bad, it wasn't going to be long.  Anyway, after installing the trigger, still no spark, disconnected the harness plug, no spark, Keep looking at that tilt limit switch, thinking, mand if that thing is shorted even with the harness plug disconnected, the switch box can find a ground.  unplugged the connector to the Merc Switch and bright blue spark.  Engine busted off with a bump of the key.  One more thing, how many poles is the tach supposed to be set to on this engine?  She's a 3 cyl 90 HP, 89' vintage, serial number begins with 333.... trying to get the tach working.  Thanks
Marc

[fitz73222]

12 poles...

[flounderpounder225]

12 poles...

Thanks Fitz...

[fitz73222]

Whats up with the BRP 90? Thats a good one; I'm interested in that solution..

[flounderpounder225]

Whats up with the BRP 90? Thats a good one; I'm interested in that solution..

I put the carbs back on last Friday afternoon after being rebuilt, she starts up and runs great on the hose.  The test will be after running her for a while on the bay, and then sitting up for a while at the beach and see how she does on re-start.  The tech told me to open the idle air adjustments 1/4 turn open if it was still having issues, I will post when we get a chance for a open water test, winds were bad last weekend, we were getting wet in the Osprey, the pontoon would have been destroyed...