Measuring stator voltage at high speed

[pastorbud]

Flywheel, stator, and trigger don't seem that hard to remove, looking at the manual. I've got a puller.

 

[Jiggz]

The compression seems to be good. Because of the difference in methodology not to mention the type and calibration of the compression gauge, differences do occur albeit between cylinders should be within 10% of each other. Have you tested for sparks using inline tester? If so, was there spark on #4? If not, what was the resistance of the trigger wire? The magnets for the stator and trigger are two different sets. The outer magnets are for the stator while the inner ones (outside of the center hole) are for the trigger.

 

[pastorbud]

There was spark on #4 when I used an inline tester. (Tester image below.)

But it lit up weak and orange, compared to the others which lit up brighter and more purple.

 

[pastorbud]

I see the manual calls for inspection of those trigger magnets to see if they've worked loose. I'm betting at least one of mine has come off. And maybe one is loose. That would explain test results, I think.

 

[pnwboat]

Pretty hard for the trigger magnet to come loose. I would suspect that you may have a bad CD module. Keep in mind the bad CD Module may be the one that is producing normal spark. The good one may be the one producing poor spark. The two CD Modules Have a blocking/isolation diode in the Kill circuit. If it goes bad, the CD Module will operate normally, but it can affect the other module causing it to appear that it is bad.

 

[pastorbud]

But why the low/intermittent/ zero DVA voltage readings? They were taken with the trigger wires disconnected from the CDI boxes.

 

[Jiggz]

I agree with PNW in that if there is spark in #4 weak it may be, it indicates the trigger is working properly. Remember, with the CD modules the trigger signal is either present or not. Meaning, either you have a spark or you don't. Now when it comes to weak spark, that will be a function of the CDM's. To validate it is the CDM, switch the CDM with a known working one and the take if from there.

 

[pastorbud]

[insert Beaver Cleaver voice] "OK, Wally. I'll try it your way." Soon! Ran outa light after work.

I reconnected everything and fired it up. Since the DVA was right there, I checked the trigger wire voltages. All around 2.5V-3.5V DC.

BTW, these are used CDI's not the originals. (I replaced one and problem endured, so I bought a second one from eBay)

I only had a little bit of light left, so I started by doing the test where you disconnect the white wire (kill switch wire) on one, then on the other CDI. If I understand the troubleshooting guide, if you disconnect one, and the spark comes back, the opposite pack is bad.

With both CDI's connected:
#1, 2, and 3 all fired good.
#4 was very dim.

With the white wire from the aft CDI (fires plugs 3 and 4) disconnected
#1 No spark
#2 Fires
#3 Fires
#4 Fires bright (!)

With the white wire from the forward CDI (fires plugs 1 and 2) disconnected.
#1 No spark
#2 Fires
#3 Fires
#4 Fires (brightness varies, goes out all together when you turn the ignition off, but engine keeps running).

Not sure that it matters, but with either white wire disconnected, the engine kept running even when I turned the ignition off, which is what I expected. But the RPM dropped. With the aft box disconnected, grounding the stator wire labeled #3 killed the engine. With the forward box disconnected, grounding the stator wire labeled #1 killed the engine. Having re-read the instructions I see that the right way to kill it was to ground the disconnected white wire. Duh.

I don't know what any of that means!

I'll do the "swap the CDI's" test on Saturday, Lord willing. Gets dark early out there!

 

[Jiggz]

The white wire on the CDM's shunts the power to ground thus mitigating flow of power to the ignition coils hence no sparks, thus shutting down the engine. That is exactly what you accomplish when you turn the ignition switch to the "Off" position, which basically connects the white wire to the black (or sometimes blue) wire that is a ground wire.

Swapping components is only useful if you know for a fact the component being swapped is a fully working component. When you switch components of unknown working status, it doesn't help in troubleshooting unless it fixes the problem. So if the problem persists after switching with unknown working status of a component, you have basically accomplished none to very little.

 

[pastorbud]

Yup. And since these are both used CDI's, I can't say for certain which, if either is working... at least from these tests. If I disconnect both white wires, at least I'll know one isn't interfering with the other and that whatever failure is present is due to the box driving that plug. Will try that and measure stator voltages next. I'm afraid I just may have two bad CDI's.

 

[pastorbud]

Hey, it works now! Took it out for a test run after work yesterday, and even got a little fishing in. After I re-ran the tests using the info I got here, I could see the problem was the forward CDI box making the aft one look bad. Then I realized that this also meant one of the "bad" CDI boxes I had taken off at the beginning was probably good. I re-installed it as the forward CDI and everything worked. So, thanks, guys! I'll probably work up a separate post with the whole story for the next guy that runs afoul of these gremlins.

 

[pnwboat]

Glad you were able to work through the problem and document your trouble-shooting process.