372 xtorq Ignition failure

[StihlEchoingHusky]

Hello all hope your days going well. I'm a little puzzled at the moment. My 372 isn't getting spark. I've tried 3 coil packs,3 spark plugs, 2 kill switches and changed out the wiring. I've also tried setting ever so slightly different air gaps between plugs and coils, starting with what the repair manual has on the specs section and increaseing/decreasing next size on my feeler gauges. I don't know if this happens(although I assume yes it does) could the magnet in the flywheel loose its ability to connect with the coil? Screws still stick to the damn thing

 

[Stem]

are you using OEM coils?

 

[ammoaddict]

Hello all hope your days going well. I'm a little puzzled at the moment. My 372 isn't getting spark. I've tried 3 coil packs,3 spark plugs, 2 kill switches and changed out the wiring. I've also tried setting ever so slightly different air gaps between plugs and coils, starting with what the repair manual has on the specs section and increaseing/decreasing next size on my feeler gauges. I don't know if this happens(although I assume yes it does) could the magnet in the flywheel loose its ability to connect with the coil? Screws still stick to the damn thing

Do you have a spark tester? You said you changed out wiring. Does that include the plug wire? Is the spring in the plug boot pressed into the wire good?

 

[StihlEchoingHusky]

are you using OEM coils?

Yes 2 brand new blue ones and 1 non OEM non limited. Non limited is something I use only for high side tuning. Other than crank case halves and spark plug oem is all I will use on this particular saw.

Do you have a spark tester? Does that include the plug wire? Is the spring in the plug boot pressed into the wire good?

In Order #1 no I do not just a voltage bulb tester and a non contact circuit tester. I tried the non contact with plug testing on cylinder. On small engines I typically hold the plug in my hand and feel for spark but not even a slight zap. #2 3 separate coils 2 of which are brand new#3 yes I've also tried using die electric grease. Prior to using the grease I did remove the boot it's self to make sure the spring was actually making contact with the wire. With 1 of the coils While it was off I gave the spring and wire and good spray of CRC electronic cleaner. And I sprayed contact cleaner on the coil Contact.

With all this said is why I'm wondering if it's the flywheel, Even though it still has a magnetic pull I'm wondering if a weakend magnet would be all it takes.

 

[lehman live edge slab]

Yes magnets can lose some strength and or switch polarity on rare occasions so I’d give the flywheel a try since you already looked
At everything else. You could also leave all the wires off the coil itself to completely eliminate the harness and switch to rule out a broken or pinched wire grounded somewhere odd.

 

[StihlEchoingHusky]

Yes magnets can lose some strength and or switch polarity on rare occasions so I’d give the flywheel a try since you already looked
At everything else. You could also leave all the wires off the coil itself to completely eliminate the harness and switch to rule out a broken or pinched wire grounded somewhere odd.

Duhh the switch is there just to kill the engine!! I have no clue why that didn't cross my mind

 

[StihlEchoingHusky]

you could also leave all the wires off the coil itself to completely eliminate the harness and switch to rule out a broken or pinched wire grounded somewhere odd.

So.. ya... Here's the thing I tired that literally right after responding.. yep no kill switch wires! Sparks like a lightning dragon. Reconnect wires nothing.... Hold up maybe I put them on the switch terminals reverse polarity or something stupid like that.... Nope. All new wires and switch from a different saw which works flawlessly...? Nothing..... I even created wiring myself using wire of the same gauge( at lease I'm pretty sure it's the same visually the core is) plus a set of thicker wire from that storehouse box of wires harbour freight sells, that maraculosly created some spark. but Im pretty sure a starter from a propane bbq left out in the rainforest for 3 years would create a bigger spark. I had to completely shut off all my shop lights just to see a faint spark. Little confusing.

I don't really know much about electric related things but could there possibly be some kind of voltage drop on the ground where is screws into the magnesium case??

 

[hacskaroly]

I don't really know much about electric related things but could there possibly be some kind of voltage drop on the ground where is screws into the magnesium case??

With the two leads coming off of the coil, one goes to the spark plug which grounds against the case. As the flywheel turns it causes the coil to create its voltages, sends to the spark plug and it sparks from the center lead to the ground lead. This will keep happening until you close the circuit (kill switch) at that time that line becomes the path of least resistance and all voltage goes to ground (case).

I believe this can happen because the spark plug has some resistance (hence the R in BPMR7A) that when the kill switch is open, the voltage can pass and spark the spark plug, but when the kill switch is closed, this is the most direct path to ground for the voltage, avoiding the spark plug. I hope that makes sense.

As for spark plugs with no R in them or internal resistance, the closed kill wire will still be the path of least resistance due to the spark having to overcome the air gap between the leads on the spark plug. This is my understanding, hopefully someone will chime in if I am incorrect.

 

[hacskaroly]

Here are some simple pictures to go with my explanation:
Normal Circuit (upper lead to spark plug then ground, lower lead to kill switch then ground - ground potential is the same between the two grounds) :

Circuit open (spark plug firing/kill switch open):

Circuit closed (spark plug not firing/kill switch closed):

If there is any part of that circuit along the way that is touching ground (exposed wiring, conductable debris...etc) then you can end up with a no-spark situation. You said with the kill switch disabled (removed from the circuit), you got full spark, however when connecting it back up you got nothing again. Using new larger gauge wire you got small spark...at least that tells you that it is working, though not where you want it. Might be due to the larger gauge wire having more resistance and only letting some voltage through. Try to match the gauge wire of the saw, not sure it might be 22 gauge (just a guess here). If you have an old cell phone charger you are not using, you might be able to cannibalize the wiring from it and have a more close in size wire to work with - at least to test.

 

[StihlEchoingHusky]

Here are some simple pictures to go with my explanation:
Normal Circuit (upper lead to spark plug then ground, lower lead to kill switch then ground - ground potential is the same between the two grounds) :
View attachment 434100
Circuit open (spark plug firing/kill switch open):
View attachment 434101
Circuit closed (spark plug not firing/kill switch closed):
View attachment 434102
If there is any part of that circuit along the way that is touching ground (exposed wiring, conductable debris...etc) then you can end up with a no-spark situation. You said with the kill switch disabled (removed from the circuit), you got full spark, however when connecting it back up you got nothing again. Using new larger gauge wire you got small spark...at least that tells you that it is working, though not where you want it. Might be due to the larger gauge wire having more resistance and only letting some voltage through. Try to match the gauge wire of the saw, not sure it might be 22 gauge (just a guess here). If you have an old cell phone charger you are not using, you might be able to cannibalize the wiring from it and have a more close in size wire to work with - at least to test.

I started it out with brand new wires straight from hlsupply. When I made my own wiring I used some wire that the core matched the actual OEM wire, (at lease visually it matched) it may have been off by a size up or down. I carefully pulled the Killswitch housing off does it look like anything is wrong?? I honestly don't know as I've stated my experience with chainsaws is minimal but I'm not seeing any arc marks or broken metal. The two "springs" in the center is the switch itself the both are clean and have good amount of springiness to them. Sorry I can't spell the correct word for some reason (boyancy?) anyways. instead of being brittle as if it were burnt out. The dielectric grease they used between the two plates is still white so I dont think it's continuously loosing or making contact. The other 2 switches look the same

 

[Shane¹]

I started it out with brand new wires straight from hlsupply. When I made my own wiring I used some wire that the core matched the actual OEM wire, (at lease visually it matched) it may have been off by a size up or down. I carefully pulled the Killswitch housing off does it look like anything is wrong?? I honestly don't know as I've stated my experience with chainsaws is minimal but I'm not seeing any arc marks or broken metal. The two "springs" in the center is the switch itself the both are clean and have good amount of springiness to them. Sorry I can't spell the correct word for some reason (boyancy?) anyways. instead of being brittle as if it were burnt out. The dielectric grease they used between the two plates is still white so I dont think it's continuously loosing or making contact. The other 2 switches look the same

View attachment 434117

Do you have an ohm meter? See if the switch has no continuity with it on and has continuity in the off position

 

[ammoaddict]

Do you have an ohm meter? See if the switch has no continuity with it on and has continuity in the off position

Good advice.

 

[StihlEchoingHusky]

Do you have an ohm meter? See if the switch has no continuity with it on and has continuity in the off position

Would a 2 prong voltage meter work? It's got a ohm symbol on it for one of the working positions.

 

[hacskaroly]

Would a 2 prong voltage meter work? It's got a ohm symbol on it for one of the working positions.

Yes, a multimeter will work, either analog or digital. Digital tend to be a bit easier because it will auto adjust to different voltages or resistances, unlike an analog which you have to adjust the dial so it will either show or not peg the meter. You can get either as cheap as $20 or $$thousands for the really really good ones. The cheap ones work fine.

 

[qurotro]

The kill switch and the wire is to connect the ground from the case to the coil. When the saw is running, the kill switch is disconnecting the circuit, hence you can try not to connect anything and the saw should run.