Good coil but still no spark

[boutselis]

I am trying to fix my 4 mix stihl string trimmer and was hoping someone could tell me what the problem might be.

I checked my coil with another unit and it sparked and ran that unit with out the stop wires hooked up. When I put it on the trimmer I am working on it won't spark.


Isn't the spark generated just by the magnets in the fly wheel passing by the contacts in the coil? Even switched the fly wheels and still no spark.

 

[Grande Dog]

Howdy,
Check for continuity between the armature of the module, and the cylinder head.
Regards
Gregg

 

[boutselis]

Howdy,
Check for continuity between the armature of the module, and the cylinder head.
Regards
Gregg

I don't have a meter to use. by "armature of the module" I am guessing you mean the crank?


If that is what you mean then how could there not be continuity between the two?

thanks for the reply

 

[borat]

Have you check the spark plug lead and cap for continuity? If it has a resistor type cap, they can and do malfunction.

 

[bplust]

Have you check the spark plug lead and cap for continuity? If it has a resistor type cap, they can and do malfunction.

+1

 

[Grande Dog]

Howdy,
I was meaning the metal part of the ignition module to the cylinder head. If they are not grounded to each other, you wont get a spark.
Regards
Gregg

 

[millbilly]

opcorn:

 

[Fish]

not too many variables to rule out here....

 

[boutselis]

Have you check the spark plug lead and cap for continuity? If it has a resistor type cap, they can and do malfunction.

I ruled that out by putting it on another unit and it ran.
Right?

 

[boutselis]

Howdy,
I was meaning the metal part of the ignition module to the cylinder head. If they are not grounded to each other, you wont get a spark.
Regards
Gregg

Ok.
Do you mean I need to have the little washers between the coil and the head?
because I do.

if thats not what you mean please explain

 

[Fish]

Every Stihl Tech here has been haunted by this/these 4 mix Gremlins, it is king of a nasty end to a poor/pathetic carreer......

Yes, the Stihl dist. came by the dealers, showing a set of videos, showing teenagers rebuilding carbs with thick leather gloves on.

And they expect me to not say anything.

You ask anything about the newer 4 mix stuff, they give you a generic link.

Ask anything about anything older than sn ms260, they tell you to buy a new one.......

 

[biggus]

1. Change spark plug with a known good one.
2. Disconnect the kill switch from the ignition module and check for spark
3. Verify proper gap between ignition module and flywheel (about the thickness of a business card).

 

[Grande Dog]

Howdy,
If you have a style with insulator washers, there must be a seperate grounding wire to get continuity between the module and the cylinder. What model are you working on?
Regards
Gregg

 

[boutselis]

1. Change spark plug with a known good one.
2. Disconnect the kill switch from the ignition module and check for spark
3. Verify proper gap between ignition module and flywheel (about the thickness of a business card).

all done and no spark. the coil is definitely good.

 

[boutselis]

Howdy,
If you have a style with insulator washers, there must be a seperate grounding wire to get continuity between the module and the cylinder. What model are you working on?
Regards
Gregg

its an fs90.

I hooked it up identically on my fs110 and the coil sparked great. I don't remember seeing a grounding wire. even on the fs110 when i disconected both wires that lead form the coil to the throttle control It sparked.

 

[boutselis]

this is driving me crazy.

 

[Grande Dog]

Howdy,
Here's some info that might help you out.
A cheapo multi-tester would be a good investment for your troubleshooting.
I'm still leaning towards a grounding issue.
Regards
Gregg

 

[lcso10]

Sheared flywheel keyway?

 

[boutselis]

Howdy,
Here's some info that might help you out.
A cheapo multi-tester would be a good investment for your troubleshooting.
I'm still leaning towards a grounding issue.
Regards
Gregg

Sheared flywheel keyway?

Nope. not the key way. thanks just the same.

Grande. that is some cool info. I am reading it now in hopes of learning something.

thanks

 

[boutselis]

No spark.

dang it all to