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Stihl electronics help

jm.

jm.

Well-known Member
Location
Dover TN
Have Stihl HS 45 hedge trimmer . No fire. Pulled the starter cover. Has external electronic module with one wire down to switch and back to ground and the spark plug wire. Have removed the module sanded the flywheel and the face of the module. Have checked the switch both ways appears good. Is there a check for the module itself. $ 35.00 on line but hate to buy one until I can confirm that is the problem. Any suggestions?
Photo attached maybe
 
Yes tried a new plug or actually two new plugs and can hold the plug wire and other hand on the metal part of the unit and still feel nothing. Pretty sure it is not firing but thought there might be a way to put a meter on it.
 
(quoted from post at 00:42:25 02/28/17) Have Stihl HS 45 hedge trimmer . No fire. Pulled the starter cover. Has external electronic module with one wire down to switch and back to ground and the spark plug wire. Have removed the module sanded the flywheel and the face of the module. Have checked the switch both ways appears good. Is there a check for the module itself. $ 35.00 on line but hate to buy one until I can confirm that is the problem. Any suggestions?
Photo attached maybe
Click to expand...

Disconnect and isolate the ground wire (to eliminate switch).
Remove sparkplug , connect High tension coil wire to it and ground plug threads against head. Spin the motor over and if no fire, try another sparkplug.
Before doing this, you should set coil to flywheel air gap at app. .012 or use a standard business card. Let the magnents pull the coil to close gap and tighten screws.
 
Jiles What you just wrote is exactly where I am. I did use a sheet of thin sandpaper as the spacer but just cannot get anything anyway I try it.. And removing that ground/switchwire was the first thing I did.
 

OK--if you like, before buying a new coil, try a method that [b:d3cf440fb3]sometimes works[/b:d3cf440fb3].

Put a few drops of two stroke oil through plug hole to lubricate piston. Spin the flywheel with a variable speed drill motor by using a socket on flywheel nut.
Being aware that you are loosening the retaining nut during this procedure. That's why a variable speed drill works best. Start spinning slow and go to full rpm for 5 seconds, or so, and remove socket under power.
I have revived some coils but not all.
You can check for ignition after you have completed this procedure.
I might add that I have replace MANY more Stihl ignition coils then any other brand.
Hope you can revive.
 
Pull the flywheel and verify that the flywheel has not rotated on the crankshaft.

The key is integral to the aluminum flywheel on an 029 that I once owned. Most likely, other flywheels are similar.

The key looked good but the metal had deformed causing the magnets to be out of time with the module. NO spark.

New $90+ flywheel (10 years ago) and it started right up.

Difficult to find even visually with the flywheel removed.

Dean
 
Now I am no genius and I asked for and appreciate all remarks //// But would the key being sheared just make the fire at the wrong time. How can the magnets move in the flywheel . I think it would still fire just at the wrong time but again I maybe wrong. I cannot get anything. I was hoping someone would how to take a multi-meter and run some test . Again thanks for the comment and wont, take me but a second to check the key , I will do anything anyone suggest before spending the $ 35 bucks.
 
Jiles is the nut on the flywheel left handed. One of the other posters wants me to check the key. I also read that the sthil coils go bad so am thinking that is where I am headed. Whole dang trimmer is not worth more that 200 new but I only use about twice a year. Sure would be good to make it fire. (Thanks for the help)
 
I am pretty sure nut is right hand thread, at least it is on all chainsaws I have worked on.
Easy to check in that it will tighten opposite of flywheel rotation.
Sheared flywheel key will throw timing off but should not prevent ignition.
Very seldom do I run into a sheared flywheel key, but may be worth checking.
 
Yes, it will.

Key was not completely sheared but flywheel had moved about 1/2 width of key. No spark.

New flywheel. Started right up.

Dean
 
I thought so too but no spark.

New flywheel. Started right up.

Made it difficult to diagnose.

I doubt that the module can be tested with a multi-tester.

Dean
 
It should fire even if flywheel is out of time with the crank, as they do not use ignition points, just timed by the flywheel magnets, so should still spark..

Try disconnecting the mag wire from the kill switch and make sure that vibration has nor worn through the wire insulation and it is grounding g to the engine case. Also do the spark check with a different / new plug. If all this checks out and still no spark, good chance the coil or internal ignition module is bad.
 
It's going to cost a lot more than $35 for the electronics testing equipment and training to find out that the module is bad. Your hedge trimmer is definitely worth more than $35.
 
..
46153.jpg
46154.jpg
 
Jiles, somehow i believe you about spinning the flywheel backwards and fixing the coil. But what ever gave you the idea to do this?
 
(quoted from post at 00:41:05 03/01/17) Jiles, somehow i believe you about spinning the flywheel backwards and fixing the coil. But what ever gave you the idea to do this?
Click to expand...

Sorry for the confusion--you spin in the running rotation.
I think the confusion started when I stated flywheel nut could unscrew when rotated.
This is because all chainsaws I have ever worked on, flywheel rotates counterclockwise looking at left side of saw and flywheel nut is right handed.
I am not sure about the engine in discussion.
Another small engine mechanic demonstrated coil reviving to me several years ago.
Good thing is--It cost Nothing to try!
 
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