395xp won't shut off with switch

[Ol' Brian]

I've got a bit of a head scratcher... maybe you guys have seen this before.

395xp, kill switch will not stop the engine. Replaced kill switch. New kill switch does not stop engine. Get out multimeter. Good continuity from blue wire to coil. Good continuity from black wire to ground. Determined that new kill switch is bad... either open circuit or sometimes very high resistance, 1.4 megohms+. Luckily, I saved the old switch, multimeter says it is GOOD. So, checked resistance from blue wire to ground bypassing the switch. Also very high resistance, again 1.4 megohms+. Resistance from Black wire ground point to engine cylinder is again high at 1.4 megohms+. Resistance from coil contact (blue wire to the engine) reads about 200 ohms.

Where would I look to find where the connection is broken or bad? Does that circuit for the coil grounding go through the AV springs, or ???

 

[sean donato]

Your not touching the leads tips when your taking the measurement are you? That will throw the readings way off to the high side. Anyway, with wires that short you should be under 1 ohm. Have you had the wires completely out of the saw and inspected them? I had an issue on my 394 and the ground wire to the switch was hanging on by a single strand. It was pretty obvious once I got it ripped apart and out.

 

[Ol' Brian]

Your not touching the leads tips when your taking the measurement are you? That will throw the readings way off to the high side. Anyway, with wires that short you should be under 1 ohm. Have you had the wires completely out of the saw and inspected them? I had an issue on my 394 and the ground wire to the switch was hanging on by a single strand. It was pretty obvious once I got it ripped apart and out.

Yeah, that all checks out. Everything appears to be as it should be, at least without tearing into the saw further. There is something causing high resistance between the ground point where the black wire screws to the body and the engine/coil. That's why I'm wondering if the circuit path goes through the AV springs... and back to the engine/coil. Maybe bar oil or something has crept into somewhere and causing a poor connection.

Might just have to start taking it apart and cleaning everything and put it all back together...

 

[pioneerguy600]

The electrical path is most commonly through wires from the coil to the switch and then back to a solid metal ground , either metal body or sometimes to the coil frame itself. I don`t have a 394 or 395 here any more to tell you exact routing of the wires. When checking wires with a multimeter I remove each end of a wire then test for ohms to make certain the wire is not broken somewhere along its length, saves me from stripping them out of the saw. If you get a reading the wire is good, no reading the wire is broken, A short length of wire will show very little resistance in a chainsaw.

 

[Ol' Brian]

The electrical path is most commonly through wires from the coil to the switch and then back to a solid metal ground , either metal body or sometimes to the coil frame itself. I don`t have a 394 or 395 here any more to tell you exact routing of the wires. When checking wires with a multimeter I remove each end of a wire then test for ohms to make certain the wire is not broken somewhere along its length, saves me from stripping them out of the saw. If you get a reading the wire is good, no reading the wire is broken, A short length of wire will show very little resistance in a chainsaw.

Yeah, like I said above, that all checks out.

It's a head scratcher.

 

[pioneerguy600]

If the spark will not ground out there is an open in the circuit, therefore not everything has checked out. Electricity will always take the easiest path to ground.

 

[Ol' Brian]

You're exactly right. That's the entire reason for this thread. All the obvious things check out. Why is there high resistance between the part of the saw body where the kill switch grounds to, and the coil/engine?

 

[pioneerguy600]

Did you remove each wire and try resistance, if one shows resistance higher than the other when both ends are disconnected from any connection points then that is the wire you need to replace, it won`t be fixed without replacement .

 

[lone wolf]

Yeah, like I said above, that all checks out.

It's a head scratcher.

Wiggle the wires while testing.

 

[Ol' Brian]

Tomorrow looks like rain, so I'll dig into it deeper tomorrow hopefully. It has to be something simple. Like I said, everything obvious is checking out good, except for the the high resistance between the ground point in the airbox where the ground wire attaches and the engine/coil.

 

[pioneerguy600]

Tomorrow looks like rain, so I'll dig into it deeper tomorrow hopefully. It has to be something simple. Like I said, everything obvious is checking out good, except for the the high resistance between the ground point in the airbox where the ground wire attaches and the engine/coil.

I like electrical mysteries, always found them intriguing and have spent many hours tracking down faults in all sorts of equipment, high resistance to me always meant the electrical path was long or varied in metallurgy so a short length of copper wire should not give high resistance readings. Did you remove the coil and clean out any gunk that may be present between the metal frame laminates and the area the coil mounts?

 

[blades]

I had a cylinder base gasket leak cause this- sneaky as sin. as to your strange high ohm readings not sure. The kill wire from the coil through switch to frame should be almost zero ohms. as that is what it does -dead short.

 

[Bob_w]

One of the ignition module mounting screws should have a ground wire on it. It should read zero to the cylinder.

 

[vtfireman85]

On a 385/390 the ground is on the case of the saw behind the flywheel if you take the recoil cover off it is clearly visible. I would check the spade terminals at the switch, i have seen many of that type terminal be loose and not make very well, particularly with any vibration. My dads Super 930 used to work intermittently, and it turned out to be just a loose connection. Even just a loose screw might give a continuity reading but in application not be a good enough connection to ground the coil.

 

[Ol' Brian]

I like electrical mysteries, always found them intriguing and have spent many hours tracking down faults in all sorts of equipment, high resistance to me always meant the electrical path was long or varied in metallurgy so a short length of copper wire should not give high resistance readings. Did you remove the coil and clean out any gunk that may be present between the metal frame laminates and the area the coil mounts?

Now you're thinking like me!! That's the next move tomorrow. Start taking stuff apart.

I had a cylinder base gasket leak cause this- sneaky as sin. as to your strange high ohm readings not sure. The kill wire from the coil through switch to frame should be almost zero ohms. as that is what it does -dead short.

It is. Cylinder base gasket leak could cause this?? Now that's wierd!!! LOL

One of the ignition module mounting screws should have a ground wire on it. It should read zero to the cylinder.

Coil base mounting screws to the cylinder read zero ohms. I'll look closer to see if there's a ground wire... I didn't notice it yesterday. Thanks for the tip!

On a 385/390 the ground is on the case of the saw behind the flywheel if you take the recoil cover off it is clearly visible. I would check the spade terminals at the switch, i have seen many of that type terminal be loose and not make very well, particularly with any vibration. My dads Super 930 used to work intermittently, and it turned out to be just a loose connection. Even just a loose screw might give a continuity reading but in application not be a good enough connection to ground the coil.

I'll look for that. I don't know how similar those saws are to a 395? We'll see!

 

[pioneerguy600]

I would really like to hear what you find, I have been working on chainsaws for a very long time and have been involved with more than a few mysteries during that time. On the very early chainsaws, back in the late 40`s some did not have on/off switches, the spark was always on and the only way to stop the saw was stick your thumb in the carb intake, those saws had a float type carb and the thumb was also the choke for starting. Saws have come a long ways since then but I still often get someone asking why the switch don`t work on their saw, since most days this is over the net I have to ask many questions that to some seem irratating but since the saw is not here in my hands I can only go by what the owner can relate to me. Case in point was a chap that we were trying to find a reason his switch was not working to stop the saw, after several back n forth messages he said he he had taken the switch out of the saw and placed it on the table, with one lead on the wire from the coil and the other on the switch he was getting a reading of continuance. That had me stumped for a bit.

 

[Bob_w]

Check 3 things... ignition module frame to cylinder, spark plug ground. Then one side of the shutoff switch to ground. Then other side of shutoff switch to module shutdown terminal.
There must be something not happening in one of these these 3 places. Basically the voltage generated by the magnets is shorted to ground. I would think most new saws work like this. I worked for RE Phelon for a time in R and D.

 

[Hipastore]

It sounds like you've done a thorough job of troubleshooting the issue with your 395xp's kill switch. Based on your description, it's possible that there is a break or damage in the wire or connection somewhere along the circuit. I would suggest double-checking all the connections and wires for any visible signs of damage or wear.

Additionally, it's possible that the issue may be related to the AV springs or other components in the engine.

 

[lone wolf]

It sounds like you've done a thorough job of troubleshooting the issue with your 395xp's kill switch. Based on your description, it's possible that there is a break or damage in the wire or connection somewhere along the circuit. I would suggest double-checking all the connections and wires for any visible signs of damage or wear.

Additionally, it's possible that the issue may be related to the AV springs or other components in the engine.

How so with the AV springs?

 

[Hipastore]

It sounds like you've done a thorough job of troubleshooting the issue with your 395xp's kill switch. Based on your description, it's possible that there is a break or damage in the wire or connection somewhere along the circuit. I would suggest double-checking all the connections and wires for any visible signs of damage or wear.

Additionally, it's possible that the issue may be related to the AV springs or other components in the engine.

How so with the AV springs?

Good question!

The AV (Anti-Vibration) springs are designed to reduce the vibration that is transferred from the engine to the handle of the chainsaw. In some chainsaw models, the AV springs are also used as part of the electrical grounding circuit for the kill switch.

This means that if one of the AV springs is damaged or disconnected, it could cause the electrical circuit to break, which could be the reason why the kill switch is not working properly in this particular case. So, it might be worth checking the AV springs and their connections to see if they are causing any issues.