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RS990

Foreman 400 weird sine wave!?

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Hi, new to the forum, I'm fixing a 1997 foreman 400 with no spark, did the usual test, check the output of the stator and the pick-up coil with a peak volt adapter and everything tested fine, I check to make sure the cdi gets power,  and it does, check wiring, so I ordered a cdi and a voltage regulator and still no spark, took out the oscilloscope to look at the sine wave of the stator output and this is what I got! Does not look normal! I don't have anything to compare to.

AC output stator.bmp

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42 minutes ago, RS990 said:

Hi, new to the forum, I'm fixing a 1997 foreman 400 with no spark, did the usual test, check the output of the stator and the pick-up coil with a peak volt adapter and everything tested fine, I check to make sure the cdi gets power,  and it does, check wiring, so I ordered a cdi and a voltage regulator and still no spark, took out the oscilloscope to look at the sine wave of the stator output and this is what I got! Does not look normal! I don't have anything to compare to.

AC output stator.bmp 146.3 kB · 1 download

 

Welcome!

 

Many things come to mind with no spark but first would be the kill switch and ignition. Everything would test fine individually but together adds up to no spark.

Have you held the plug while turning it over? Feel anything? Are we talking super weak or nothing? If nothing I would almost rule out the stator...

 

If you haven't already please feel free to download a service manual and check out the no spark section. Here is a link to the service manuals thread where you can download a free PDF copy.

 

 

Let us know how it goes!

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21 minutes ago, RS990 said:

Hi, new to the forum, I'm fixing a 1997 foreman 400 with no spark, did the usual test, check the output of the stator and the pick-up coil with a peak volt adapter and everything tested fine, I check to make sure the cdi gets power,  and it does, check wiring, so I ordered a cdi and a voltage regulator and still no spark, took out the oscilloscope to look at the sine wave of the stator output and this is what I got! Does not look normal! I don't have anything to compare to.

AC output stator.bmp 146.3 kB · 3 downloads

welcome, and was all these parts oem from honda ?, or china junk from ebay/amazon ?.

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Welcome to the group. 

 

I know what a sine wave looks like and that looks somewhat OK. I'd go through the trouble diagnosis shown above in the service manual. 

 

I have a little spark tester I use or you can just hold the plug against the head(I can vouch saying it only hurts a bit if it decides to ground through you).... The little window tester I have is a bit less stress and works great.

 

My favored tester looks like this...

 

 

Snap80.jpg

Edited by 87Iroc
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22 minutes ago, RS990 said:

took out the oscilloscope to look at the sine wave of the stator output and this is what I got! Does not look normal! I don't have anything to compare to.

 

Pay no mind to the stator output... it produces AC voltage for the charging system and has nothing to do with the ignition. The Foreman 400 has a DC-CDI ignition system so it requires a good battery be installed. Check the ignition fuse, neutral switch, IGN switch and the Kill switch first using a multimeter. Check the G/W wire at the stator connector to verify the ground, then test the pulse generator using a peak voltage adaptor. There should be battery voltage measured at the CDI connector Bl/W wire on the harness side of that connector. The Lg/R wire should show a ground on the CDI connector with the trans in neutral. The IGN coil can be tested per instructions in the service manual.

 

If your CDI is a genuine Honda part number its pretty easy to diagnose the ignition. But if ya got any aftermarket parts (china) on it you'll need to replace all of those parts with OEM Honda parts to get the ignition working. Let us know how it goes if ya can.

 

 

ign.png

yellow-yellow-green.png

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Welcome to the forums !    Retro looks like he fixed you up !!! 

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Yes I have the service manual, I followed the procedure in the manual, what's puzzle me is the AC sensor line, the green wire in the 5p connector and the yellow wire in the 4p connector of the ICM should be open but I have some resistance, if I unhook the VR the resistance goes away, manual says nothing about unhooking the VR, tried with a new regulator with the same result, What's the AC sensor line for? I did not test the ignition coil because I don't have any signal that goes to the coil. The ICM is OEM the VR is aftermarket. I do have 12v to the ICM, the Lg/R wire does go to ground. FWIW I have over 25+ year of experience working on ATV'S and Snowmobiles but we learn something new everyday!  😁

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Welcome to the forum, looks like you are getting what you asked for........

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19 minutes ago, retro said:

 

Pay no mind to the stator output... it produces AC voltage for the charging system and has nothing to do with the ignition. The Foreman 400 has a DC-CDI ignition system so it requires a good battery be installed. Check the ignition fuse, neutral switch, IGN switch and the Kill switch first using a multimeter. Check the G/W wire at the stator connector to verify the ground, then test the pulse generator using a peak voltage adaptor. There should be battery voltage measured at the CDI connector Bl/W wire on the harness side of that connector. The Lg/R wire should show a ground on the CDI connector with the trans in neutral. The IGN coil can be tested per instructions in the service manual.

 

If your CDI is a genuine Honda part number its pretty easy to diagnose the ignition. But if ya got any aftermarket parts (china) on it you'll need to replace all of those parts with OEM Honda parts to get the ignition working. Let us know how it goes if ya can.

 

 

ign.png

yellow-yellow-green.png

if the stator is making AC voltage, and his china reg/rec is not converting it to dc ?, then this would have me thinking it's the reg/rec.

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3 minutes ago, RS990 said:

what's puzzle me is the AC sensor line, the green wire in the 5p connector and the yellow wire in the 4p connector of the ICM should be open but I have some resistance

 

The Green with White stripe wire in the 4P stator connector should show a ground. The voltage regulator should be plugged in and the Yellow wire at the CDI connector should show an AC voltage signal while the motor is being cranked over by the starter. If ya got a china voltage regulator on it that Yellow AC signal line wire may be shorted.... cheap china parts generally DO NOT work on Honda ATVs. When china parts do happen to work they commonly fry themselves and many times, fry other genuine and expensive electrical components.

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5 minutes ago, shadetree said:

if the stator is making AC voltage, and his china reg/rec is not converting it to dc ?, then this would have me thinking it's the reg/rec.

 

The OP is diagnosing a no spark condition on a DC-CDI... not a charging system issue. You're speedreading again shade. Try your good eye! LOL 🙂

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The customer brought me the parts so i'll ask him if he can return the VR and get an OEM but is budget is limited. AC sensor line that does to the ICM if it's not present will it cause a no spark?

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I'm not to familiar with Honda's ignition system, I've read on another forum that if the VR goes bad it can cause no spark situation. Why?

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1 minute ago, RS990 said:

The customer brought me the parts so i'll ask him if he can return the VR and get an OEM but is budget is limited. AC sensor line that does to the ICM if it's not present will it cause a no spark?

 

Yep, the AC sensor line must show an AC voltage while cranking with the starter, else the CDI will shut down. Maybe your customer still has the OEM voltage regulator that was on it? I'd swap the old one back on (after checking it for shorted/open diodes) before I'd spend any more time on diagnosing it with a china part on it.

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6 minutes ago, RS990 said:

I've read on another forum that if the VR goes bad it can cause no spark situation. Why?

 

If the diode(s) on that yellow AC sensor line inside the VR shorts out, then the CDI shuts down.

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Yes I still have the OEM VR, will check tomorrow at the ICM for AC signal and report back. Any way to test the VR?

 

This is the pulse generator sine wave, looks good!

 

Pick-up coil.bmp

Edited by RS990

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8 minutes ago, retro said:

 

If the diode on that yellow AC sensor line inside the VR shorts out, then the CDI shuts down.

Thank Retro, I'm a man of logic and must understand how thing works and why!  👍

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First verify that the yellow wire that goes to the CDI produces an AC voltage while the voltage regulator is unplugged. If no AC voltage is observed then ya either have a burnt stator, or the G/W wire (stator ground) is broken somewhere between the CDI connector and the Stator. If you see AC voltage, plug the VR back in and test for an AC voltage on the yellow wire at the CDI connector again.

 

You can generally perform a basic regulator diodes test by measuring resistance with your multimeter with one lead on the Red output wire in the connector and the other lead on each of the three Yellow wires in the connector. Reverse your multimeter leads for each yellow wire that ya test. You should see a low resistance (continuity) with current flowing in one direction and a very high resistance (no continuity) while your leads are swapped and current is flowing the other direction through the regulator. Verify that the green wire in the VR connector provides a stator ground too, of course.

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13 minutes ago, RS990 said:

This is the pulse generator sine wave, looks good!

 

Yup, that looks perfect!

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2 minutes ago, retro said:

First verify that the yellow wire that goes to the CDI produces an AC voltage while the voltage regulator is unplugged. If no AC voltage is observed then ya either have a burnt stator, or the G/W wire (stator ground) is broken somewhere between the CDI connector and the Stator. If you see AC voltage, plug the VR back in and test for an AC voltage on the yellow wire at the CDI connector again.

 

You can generally perform a basic regulator diodes test by measuring resistance with your multimeter with one lead on the Red output wire in the connector and the other lead on each of the three Yellow wires in the connector. Reverse your multimeter leads for each yellow wire that ya test. You should see a low resistance (continuity) with current flowing in one direction and a very high resistance (no continuity) while your leads are swapped and current is flowing the other direction through the regulator. Verify that the green wire in the VR connector provides a stator ground too, of course.

Good, will check tomorrow if diodes are good, normally should read open circuit one way and about 0.5v the other in diode mode.

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8 minutes ago, retro said:

First verify that the yellow wire that goes to the CDI produces an AC voltage while the voltage regulator is unplugged. If no AC voltage is observed then ya either have a burnt stator, or the G/W wire (stator ground) is broken somewhere between the CDI connector and the Stator. If you see AC voltage, plug the VR back in and test for an AC voltage on the yellow wire at the CDI connector again.

 

You can generally perform a basic regulator diodes test by measuring resistance with your multimeter with one lead on the Red output wire in the connector and the other lead on each of the three Yellow wires in the connector. Reverse your multimeter leads for each yellow wire that ya test. You should see a low resistance (continuity) with current flowing in one direction and a very high resistance (no continuity) while your leads are swapped and current is flowing the other direction through the regulator. Verify that the green wire in the VR connector provides a stator ground too, of course.

The Service Manual should have more about the AC sensor line, there is not much in there to do a proper diagnostic.

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2 minutes ago, RS990 said:

normally should read open circuit one way and about 0.5v the other in diode mode.

 

If you were checking diodes out of circuit thats how a diode should behave. But there are other components inside that regulator so the low/high resistance test is generally a more reliable method for testing the VR. Try both methods, if one does not provide you with any meaningful results the other likely will.

 

1 minute ago, RS990 said:

The Service Manual should have more about the AC sensor line, there is not much in there to do a proper diagnostic.

 

Ya, I don't think the FSM even explains what that AC line is for...? The wiring diagram shows its purpose though.

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2 minutes ago, retro said:

Ya, I don't think the FSM even explains what that AC line is for...? The wiring diagram shows its purpose though.

That why I was suspecting the stator with that weird sine wave, I thought that maybe the ICM doesn't like that signal.

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That sine wave may indicate there is a bad stator ground? Does the G/W wire supply a good solid ground?

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