Measuring stator voltage at high speed

pastorbud

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Trying to diagnose an engine that runs OK in the back yard, but has ignition problems at higher RPM's. I'm reading the troubleshooting guide from CDI Electronics (see link below). It reads
"HIGH SPEED MISS:
1. Using the CDI meter with the 511-9773 peak reading adapter, (or CD-77) and 511-9770 piercing probes, DVA check stator voltage to each pack
at high speed. If it exceeds 400 volts, replace the pack."

I have piercing probes already. I can get my hands on a DVA multimeter. But I don't understand why I need to use the piercing probes. If I am checking the voltage "at high speed", obviously the engine is running.... so why can't I just measure the voltage at the screw posts where the stator wires connect to the CDI wires?
 

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pnwboat

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You don't need piercing probes. Just use the screw terminals like you suggested.
 

pastorbud

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Thanks! So, do I measure across the blue and yellow wires, or across blue and ground and yellow and ground?
 

pastorbud

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'Nuther newbie question. I'm building the DVA adapter describe at link below. Now, where it says "Red test lead" and "Black test lead".. is that the side that connects to the multimeter? Or to the component? In other words, which end does the multimeter go on?
 

pastorbud

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Can't seem to get the link embedded right. It's at http:(slash)(slash)forums.iboats.com/forum/engine-repair-and-maintenance/johnson-evinrude-outboards/380403-how-to-make-a-dva-adapter-for-multimeter
 

pnwboat

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This should help. Note: The comment under "To Multimeter". It says to set the scale to DC volts. This was confusing to me at first because the stator output is actually AC voltage but with the DVA you use the DC volt scale.

DVA schematic.jpg
 
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Nordin

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The adapter make it to DC voltage by storing it in a capacitor. The actual AC reading from the stator is just about 1 voltage more than the reading in DC.
So you use the DC setting at the voltmeter to read the value from the stator.Then you have to put the leads at positive and negative at the VOM.
If you switch the red and black leads you get a negative (minus) value at the VOM.
 

pastorbud

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OK, one more... when the trouble shooting guide attached above reads:

Measure the DVA voltage DVA Reading
Blue Yellow 180V +
Blue ) Engine Ground Open 180V + Connected (≤ 2V disconnected)
Yellow Engine Ground Open 180V + Connected (≤ 2V disconnected)
Orange Green 0.5V +
Red White/Green 0.5V +

All these readings are done
1) with the stator wires connected to the power packs as usual, except for where they're marked "disconnected" (that is the blue to ground, and yellow to ground readings)?
2) with the engine idling?(except for the high-speed reading, which is the main one I'm interested in.) or just turning it over with the ignition on, but not running? (that's how I check auto ignitions, usually.) Obviously the "disconnected" readings can't be done with the enging running.
 

pnwboat

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The readings are taken with the stator wires connected to the CD modules as they are normally connected. I don't know if this is correct but I check the voltage at both cranking speed (not actually starting) and at idle for the minimum 180VDC. Then rev the motor up to around 3000 RPMs to check for the maximum output to be less than 400VDC.

Most of the time you can verify the stators condition by doing a simple resistance check. The DVA voltage is a more comprehensive test but not absolutely necessary 100% of the time. Having said that, I've been lead astray a few times by DVA voltage readings. Probably due to my inexperience and the fact that the stator voltage changes with engine RPM, but I usually check the resistance first and if the readings are borderline, I also check the DVA voltage. Also be aware that if the engine/stator are warm from running, the stator resistance readings will be slightly higher than if cold.
 

pastorbud

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All good to know! I'm fighting intermittents. Already put on two used CDI boxes from two different sources, new plugs and new terminal ends and problem endures. Testing now from the stator "out" to the coils.
 

pnwboat

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Those intermittent issues are the hardest to pinpoint. If it is electrical, make sure all of your grounds are in place and making good contact. Also look at the trigger wires and make sure you don't have any bare wires that may be intermittently touching the block when you move the throttle. As you advance the throttle, it rotates the trigger assy. to advance the timing. You can also measure the trigger coils and stator coils resistance while wiggling the wires at the same time to pinpoint any broken conductors inside the insulation.
 

pastorbud

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And the award for most hillbilliest homemade DVA adapter goes too... (Hey, it saved me a trip to Radio Shack for a breadboard and work box.)
!DVAadapter.jpg
 

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pastorbud

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Started measuring after work tonight. Just measuring cranking voltage for now, since CDI's are disconnected. Stator wires produced over 190V (s'posed to be 180V+). One set of trigger wires produced 3.5V (s'posed to be 5.0 V). Next set of trigger wires read 0V at first. Then it got dark and my battery ran outa juice. I put the charger on it and came back inside.
 

pnwboat

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The most unique DVA that I've ever seen! As long as it does what it was designed to do, that's all that matters.
 

pastorbud

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Well, my backwoods DVA seems to work. I took another stab at measuring trigger voltage. They're all supposed to 0.5V+. I ran the tests three times, cranking it with wires disconnected.

First result were done cranking on one battery with the ignition in off position.
Then I realized the ignition was off.... but that shouldn't mattery, with trigger wires disconnected... just to be safe, I turned ignition on (which also turns the console lights on, so it draws the battery more) and ran again.
By then, it was cranking slow, so I turned the battery switch to both, and ran again.

(BTW, all the resistance readings on the stator and trigger wires were within tolerance, and none of them varied when I wiggled the wires.)

Results of the three trigger voltage tests:

Trigger #1-- 0.5V, 0.38V, 0.62V (battery draw-down on second reading is obvious!)
Trigger #2-- 0.0V, 2.8V, 0.0V
Trigger # 3-- 0.4V, (missing data on 2nd test, getting dark!), 0.60V
Trigger #4-- 0.0V, 0.0V, 0.0V

Looks like #2 explains how it "kicks in" and out when running. And #4 is a goner.


I'm thinking I at least need a new trigger assembly. Could anything else cause this?

I happen to have one on a parts motor in the back yard. However, if I'm gonna pull two flywheels (one to get the old trigger assembly out and one to install it in my current motor), I think I'd just as soon put in a new one. My parts motor is the same vintage as my current motor, so I'm afraid I'll be right back where I started next year if I go with the used one.

'course, with old motors, I suppose you never really know.
 
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pastorbud

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1987 Force 125 HP. Not sure why the trigger wire resistances are good but it produces no voltage on some cylinders. It occurred to me there might by a problem in the flywheel with the magnets, but don't they also "drive" the stator? How could the stator be producing 180V+ if there were a problem with the magnets?
 

pastorbud

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I also tested compression (cranking with three plugs in and the plug being tested out and grounded) and they were below what manual recommends:
#1=120 lbs, #2 and 3=118 lbs, #4=110. Manual calls for 125 lbs min. But it ran fine before the ignition problems... pushed my 18.5 foot center console at about 30 mph on the GPS.
 
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