1995 125hp Mariner, no spark, DVA & Resistance readings

49Mercury

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This 1995 Mariner 125HP abruptly failed to start out on the Sound a month ago. I had just cleared a lobster pot rope from the propeller and the motor was up out of the water. I was cranking it for about 10 seconds before remembering it was all the way up, but on putting it back down, it wouldn't start. Back home, there was no spark in any cylinder with vigorous cranking (using a CDI spark tester), with the black-yellow wire being disconnected. All the voltages were correct from the key switch wires to the engine. Got a Mercury DVA spark tester adapter, used with my Fluke 179 meter to check voltage readings from either switch box terminal, or from the stator wires themselves when disconnected from the switch box (number in parentheses). All voltages while vigorously cranking with good battery.

My DVA and resistance measurements of stator:
Across all 4 coils, zero.
Stator Red 28 (27), Red-White 24(24), Blue 190 (196), Blue-White 210 (222).
Resistances: B-BW, 6050 (but variable, see following), R-RW consistently 92. I took off the stator and took it into the house and measured resistance several times over a week. Sometimes the B-BW was 16000, or 47000 ohms, not 6000.

From the Mercury Manual about this stator:
coils, 150-250 V
Blue, 200-300V
Red 20-90V
B-BW 6800-7200 ohm
R-RW 90-140 ohm

So the blue voltages are slightly low, but it is cranking not running. And BW-B resistances either slightly low, or very high but out of range.

The stator is black, number 398-9710A31.
The current SB is only 4 yrs old and was hardly used in most of that 4 yrs so it is pretty new.
If the stator is all that is bad why is it still generating approximately correct voltages and why isn't there some spark?
Should I get a CDI stator part 1749710K1 or stick with OEM? CDI SB has heavier wire which is not encased in plastic, or should I stick with OEM.
Should I buy a Mercury switch box or get a CDI one? Any opinions about OEM vs CDI are welcome.
If the switch box is bad why did it get ruined so quickly?

Thank you in advance.
 
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49Mercury

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But should coil resistance in a stator vary or be constant? In my case 6000 ohms one time and 16000, or 46000, the next? does that automatically mean the stator is bad? Is it possible for a stator to make the right voltage but not sustain whatever current is required for a spark?
 

49Mercury

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Can anyone comment on whether they think my stator is bad? See my resistance readings, they are variable and way outside those in the manual.
 

sutor623

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I have seen stators with resistance out of spec work just fine. But, typically, in my experience, a shorted stator will have LESS resistance, not more. Stupid question, but are you sure your meter is set to the correct decimal?

The only time I have seen coil resistance in a stator change, is when it goes from cold to warm and vice versa.

Did you throw a timing gun on it to make sure you didnt shear a key? Are you cranking 250rpms or more? I bet your timing is off.

I typically prefer CDI to OEM.
 

49Mercury

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Thank you.

I'm sure the ohm readings are right. It is a fluke 179 with only one setting which reads out the ohms with decimals and either kOhms or mOhms if necessary. Right now the stator is in the house at about 60F and Blue-BlueW reads 66.0 kOhms (66000). First I've noticed, is that if I bend the wire pack around where it goes into the stator, i can make the resistance go to about 128,000 ohms or somewhere in between 66000 and 128000. Some other times it has been 6000 when outside mounted on the engine, as stated above. The reading should be 6800 according to the manual. So it looks right now (66000-120000) as if there is practically a break somewhere in the Bl-Bl/W stator wiring, in contrast to a short. Could this not lead in use, to a correct voltage but almost no ability to deliver current?

The red -red white resistance is always 92-93 ohms and doesn't change when the wires are manipulated as they enter the stator.

No I didnt use a timing light. If the key is that where the flywheel keys to the shaft, no it is not sheared it is in good shape. I've had the flywheel and stator on and off several times and the key is good.

I don't know what the RPM is when cranking, how would I measure? It is always a fully charged battery with as fast a cranking speed (by ear) as I am ever used to, in using this engine.

Thank you for your attention and I would appreciate your input again on the stator issue based on my answers . If it is looking bad I would try replacing it first rather than the switch box. Is there an issue keeping the OEM switch box if I get a CDI stator?
 
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sutor623

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No, CDI and oem will work good together. I like the CDI stators very much. They stay cooler than the epoxy covered garbage from the factory. If your resistance is changing when you bend the wires, then you have found the issue in my opinion. You either have corrosion in there or a bad connection between the annealed wire and leads. I have rewound many stators in my day, and the one thing that pisses in my oats are these epoxy covered stators because they are nearly impossible to repair.
 

sutor623

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Also, the high voltage could be arcing the "break" in the wiring, and could explain how you have good voltage and high resistance.
 

49Mercury

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Thanks again. One more question. The last time the motor was running, I was repositioning the boat to pull up an anchor, and somehow got turned around with 2-3 wraps of the anchor line around the prop (not a lobster pot as I stated in the OP above). I don't believe this stopped the motor, I can't remember. After raising the motor completely to clear the line, I tried unsuccessfully to start it again for maybe 10 seconds with the motor out of the water before noticing. It wouldn't start again, this was the last it ran.

Could either of these insults have damaged the stator, or anything else that might be relevant to my no spark situation?
 

sutor623

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I don't see how the two could be related, honestly.

So to recap, you do not have spark jumping a 7/16" gap on ANY leads? Yet, you have voltage coming from the stator? Sounds like Fazt may have been right on this one. If that voltage is being produced, it HAS to be getting cut off somewhere. It may just be the switchbox, even if it isnt very old. Did you check the DVA of the trigger yet? How about resistance there? Cracked magnet there?
 

sutor623

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Have you gone to CDI troubleshooting section yet to narrow down the issue? You have a fluke meter and DVA meter, so that is all you need to do the basic tests of all electrical components.
 

49Mercury

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Yes, I've done the CDI and OEM testing. The values are all reported above.

I would be happy to answer any details about either testing sequence if anyone sees something I didn't report.

What's clearly out of line is the stator resistance. 68000-128000 ohms mostly, instead of 6800 ohms (OEM reference resistance). I don't see how that could be normal, that much off isn't going to be temperature related.

I ordered a CDI stator today.
 

sutor623

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I know you did the CDI tests for the stator, but what about trigger and switchbox?
 

49Mercury

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I apologize especially to those who responded above, for being AWOL for the last month. Since my last post, I received and installed a new CDI stator. Still no spark in any of the 4 cylinders.
New measurements with the new CDI stator, following along the CDI testing sequence. No spark in any cylinder in any of these tests.


DVA voltages for Red, Blue, Blue-White, Red-White stator wires:
34, 174, 194, 31 at switch box posts. Outside temps in 60s several weeks ago.
32, 163, 182, 30 at switch box posts. Today, 40 deg F.
32, 164, 184, 29 at each stator wire, each being disconnected from switch box, other 3 connected. Today, 40 deg F.
32, 160, 182, 30 volts at switch box posts. Today, all 5 wires disconnected from Voltage Regulator.

Conclusion the new stator is working and the voltage regulator is not the problem.


Looking at the TRIGGER diagnosis section, DVA voltages and resistances appear close enough to spec:
purple-white 4.9V connected to SB, 6.2V disconnected. Resistance is 780 ohms. Spec 800-1400 ohms.
blk-blk 4.9 V connected to SB, 6.5 V disconnected, resistance 770 ohms. (my wire color, diagnosis guide says one is Brn and other white black). Spec >4 V.
purple, white, black, black DVA voltages each to ground, are 2.9, 2.9, 3 and 3 V. Spec >1V.

Conclusion the trigger voltages and resistances seem good.


Should I get a new switch box?
 
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