ArboristSite.com Sponsors


testing ignition module

roundhead

roundhead

ArboristSite Operative
Joined
Jan 3, 2012
Messages
288
Location
Sunny Florida
I am not getting any spark...is there a way to test the ignition module on a stihl? I used a voltmeter and when I pull the rope, there is no reading.
thanks
 
Karl Robbers

Karl Robbers

ArboristSite Operative
Joined
Sep 24, 2010
Messages
248
Location
Lebrina Tasmania Australia
I am not getting any spark...is there a way to test the ignition module on a stihl? I used a voltmeter and when I pull the rope, there is no reading.
thanks
Short answer is no, other than to pull the plug, open the electrode gap a little, earth the plug out to the cylinder and give it a few pulls while watching for spark. I strongly suggest that you also disconnect the kill wire while doing this as this can stop spark if there is a wire or switch fault. If you get spark without the kill wire attached but lose it when you re attach the kill wire this means the kill wire is shorted or the switch is faulty.
It may also pay to check the gap between the module and the flywheel.
Failing all this, it's a new module.
 
ndlawrence

ndlawrence

ArboristSite.com Sponsor
Joined
May 9, 2011
Messages
958
Location
Tennessee
Very simple, Disconnect the kill switch wire, take the plug out of the cylinder and ground it back to the cylinder and watch it as you quickly pull the starter rope.
 
roundhead

roundhead

ArboristSite Operative
Joined
Jan 3, 2012
Messages
288
Location
Sunny Florida
Very simple, Disconnect the kill switch wire, take the plug out of the cylinder and ground it back to the cylinder and watch it as you quickly pull the starter rope.
thanks I did try that, just not w/o disconnecting the kill switch. I will give it a shot. it is for a BR 400 backpack blower so I have never worked on one of these before. the parts are not as many as my saws. the flywheel is alittle bit tougher to get to.
 
ndlawrence

ndlawrence

ArboristSite.com Sponsor
Joined
May 9, 2011
Messages
958
Location
Tennessee
thanks I did try that, just not w/o disconnecting the kill switch. I will give it a shot. it is for a BR 400 backpack blower so I have never worked on one of these before. the parts are not as many as my saws. the flywheel is alittle bit tougher to get to.
Oh alrighty, try it without the kill switch wire, sometimes the switch will go bad or the wire will short itself out.
 
Old Fart

Old Fart

New Member
Joined
Mar 24, 2016
Messages
3
Age
69
Location
Montgomery, TX
Short answer is no, other than to pull the plug, open the electrode gap a little, earth the plug out to the cylinder and give it a few pulls while watching for spark. I strongly suggest that you also disconnect the kill wire while doing this as this can stop spark if there is a wire or switch fault. If you get spark without the kill wire attached but lose it when you re attach the kill wire this means the kill wire is shorted or the switch is faulty.
It may also pay to check the gap between the module and the flywheel.
Failing all this, it's a new module.
 
Old Fart

Old Fart

New Member
Joined
Mar 24, 2016
Messages
3
Age
69
Location
Montgomery, TX
It seems that people are in the unit replace mentality more and more each day. As I on the other hand have very little funds and a lot of time. I looked on this site for help to test a ignition coil on a chain saw. All of the responses recommended toss it and replace with new when the person asking just wanted to trouble shoot the problem on the bench. I thought about it and felt it deserved a lucid response. So here it is. Most if not all small 2 cycle engines today use a similar ignition system setup. and there is a simple way to bench test these with a volt ohm meter. For a simple understandable description, the module itself contains two coils of wire. On one end of each coil both are grounded together to the laminate frame that attaches it to the engine block. Of the two coils they are described as a primary and secondary. The primary obtains the charge when the magnets pass the poles when starting via pulling on the rope. The charge induced into the primary field is then boosted by the secondary to create the higher voltage needed to create the spark at the plug.
For Bench Testing : The primary resistance is somewhere between 175 to 250 OHMs between the laminates and the little kill lug sticking out of the coil. The secondary coil resistance is about 2200 to 3000 OHMs between the laminates and the spark plug connector.
Now we have that information but lets look a bit deeper before we discard the module completely as bad. Because I have more time than money and in a lot of the instances it is a long way from the woods back to civilization sometimes. Check the spark plug wire for a bad connection. I have discovered that many ignition coils are discarded because the connector from the plug to the wire has vibrated so much that the connection becomes intermittent and the resistance get way higher or as you can see it when you test the secondary by attaching clips from the meter to the laminate and plug connector and gently bend the plug wire between your fingers and watch the meter resistance jump up and down as you check from one end to the other of the plug wire for breaks in the wire. Most often it's just the connector on the plug that needs refitting.

I hope this helps the others like me that have more time than money

The Old Fart in Texas
 
hotshot

hotshot

ArboristSite Operative
Joined
Apr 11, 2009
Messages
2,413
Location
Midwest
Well, you are an old fart, as that only works on older saws that use points or an external trigger.

Most current CDI type coils (post 1970s) have Darlington transistors, diodes, capacitors & resistors
in them, not just two simple windings.

Heres a sample diagram for a Stihl CDI type coil from the 1970s.
 

Attachments

Old Fart

Old Fart

New Member
Joined
Mar 24, 2016
Messages
3
Age
69
Location
Montgomery, TX
Well, you are an old fart, as that only works on older saws that use points or an external trigger.

Most current CDI type coils (post 1970s) have Darlington transistors, diodes, capacitors & resistors
in them, not just two simple windings.

Heres a sample diagram for a Stihl CDI type coil from the 1970s.
Both systems still use a primary and secondary winding, also the resistance values are true in either cases.
I also validated the values before I posted, anyway it is just meant to be just a description that helps to understand how it works without confusion as to what's in there and to provide a simple way to test for functionality.
Old fart
 
SteveSr

SteveSr

Addicted to ArboristSite
Joined
Mar 3, 2003
Messages
1,424
Location
Raleigh, NC
Website
Visit site
The newer coils have a PIC microprocessor in them... probably to handle the timing advance curve and programmable rev limiting. After spending a career in electronics I was surprised when a Stihl rep showed an unpotted ignition coil assembly and I recognized the markings on the processor on the printed circuit board to be a Microchip PIC processor.
 

Okie

Addicted to ArboristSite
Joined
Mar 7, 2015
Messages
1,144
Age
76
Location
Oklahoma (USA)
Wow, this is my kind of thread. I just learned some real cool stuff. Thanks to all!
I agree with SteveSr: The newer coils have a PIC microprocessor in them...(and lots of other stuff now days use solid state devices buried inside and sealed)

Not much learned here for me. (and I've seen the old style ignition system coils several times test ok using a test meter and ignition coil/Magneto tester and not work correctly on the equipment.) (weak or erratic usually) I've got all kinds of electronic test eq, coil testers, Magneto testers, condenser testers, and real world test when all is said and done is too sub with a know good part and quit farten around.
When I find something bad/intermittent/erratic especially electronic ignition module systems for instance I replace it or sub with know good one and quit FARTING around wasting time.
and I'm a electronic tech, electrician, mechanic.
 
SteveSr

SteveSr

Addicted to ArboristSite
Joined
Mar 3, 2003
Messages
1,424
Location
Raleigh, NC
Website
Visit site
The newer coils have a PIC microprocessor in them... probably to handle the timing advance curve and programmable rev limiting. After spending a career in electronics I was surprised when a Stihl rep showed an unpotted ignition coil assembly and I recognized the markings on the processor on the printed circuit board to be a Microchip PIC processor.
A couple of more thoughts... Since Stihl uses solid conductor ignition wire (NOT resistance wire) you can still check the secondary winding (and wire) to the spark plug for continuity with an ohmmeter as a previous poster suggested. However, this will not check for coil breakdown at high voltage under operating conditions. Since everything these days is vacuum potted I would think breakdown would be pretty rare.

All of the Stihl ignition systems that I have seen are surprisingly "weak" when compared to older outdoor equipment and automotive ignitions. This is the main reason that the plug gap is specified at a measly .015"-.020" which is another thing to check. My old automotive plug gap gauge doesn't even go down this low. I think the reason for this is that hair fine copper wire for the secondary on the coil is expensive and there is limited mechanical space to put it in small outdoor equipment like saws and trimmers.
 
backhoelover

backhoelover

Free service manuals and service tool info
Joined
Jan 2, 2013
Messages
2,680
Age
34
Location
north carolina
what i see alot of is the stages going out now revving up. first time i came into this i though it was the crab put a new one on nothing. called a gold tech buddy that is when i found out about the stages. from what i know there is no know documentation covering this (wish there was) he stated that they didnt talking about this till gold tech class.
 
Termite

Termite

Time To Launch
Joined
May 11, 2008
Messages
1,737
Location
milltown indiana
I was using one of those testers with a neon light in series with the plug. The saw would start easy and make one successful cut and then die on the second. With this neon light I could see the spark stop. When I replaced the plug the problem went away. I will not tell you all the things I did before replacing the plug.:rare2:
 
SteveSr

SteveSr

Addicted to ArboristSite
Joined
Mar 3, 2003
Messages
1,424
Location
Raleigh, NC
Website
Visit site
I was using one of those testers with a neon light in series with the plug. The saw would start easy and make one successful cut and then die on the second. With this neon light I could see the spark stop. When I replaced the plug the problem went away. I will not tell you all the things I did before replacing the plug.:rare2:
BTW, a neon light would make a good tester and would be much easier to see than looking for a blue spark while the plug is sitting exposed on the side of the block

Interesting failure... The plug would have to go open circuit for the light not to flash i.e no current for the bulb. I wouldn't think that a shorted plug (much more likely occurrence) would NOT kill the coil output completely... but it might. This would be an interesting test with your neon light.
 

Okie

Addicted to ArboristSite
Joined
Mar 7, 2015
Messages
1,144
Age
76
Location
Oklahoma (USA)
BTW, a neon light would make a good tester and would be much easier to see than looking for a blue spark while the plug is sitting exposed on the side of the block

Interesting failure... The plug would have to go open circuit for the light not to flash i.e no current for the bulb. I wouldn't think that a shorted plug (much more likely occurrence) would NOT kill the coil output completely... but it might. This would be an interesting test with your neon light.


I do not trust neon inline spark indicators.
I've seen the neon type flash when the spark was too weak for engine run.
I could place the neon tester on a good ignition system and the neon flash would be little brighter as compared to the bad weak one. Not easy to tell the difference in brightness of a lieing neon tester.
If ignition was going completely dead intermittently, the neon flash the are ok but they will lie to you about weak ignition.

and YES a bad spark plug can sure make you feel weak after you have replaced and tested all the other stuff first.
 
a. palmer jr.

a. palmer jr.

Tree Freak
Joined
Apr 8, 2007
Messages
13,559
Location
Southern Indiana
Don't know about backpack blowers but on chainsaws the ignition modules are super cheap for Stihl, much cheaper than buying the equipment to test a module. Ebay has the modules usually for less than $20.
 

Okie

Addicted to ArboristSite
Joined
Mar 7, 2015
Messages
1,144
Age
76
Location
Oklahoma (USA)
Don't know about backpack blowers but on chainsaws the ignition modules are super cheap for Stihl, much cheaper than buying the equipment to test a module. Ebay has the modules usually for less than $20.
Right: You can usually find parts (all kinds of parts) on flea bay by careful searching so as to test with out spending a arm and a leg.
Some of the cheapo China clone ignition systems are only good (maybe) as a sub for testing, then try to find a OEM part.
For example Stihl china clone modules on flea bay are around $15 with free ship, but NEW OEM Stihl modules are over $100.

I cannot trust China clone ignition system modules for long term use though. Also very few places will have any type of warranty on electronic ignition parts and if you are thinking about warranty on such you better ask first, therefore when your money leaves your pocket it's gone/gone.

I've had many electronic ignition clone failures to have any trust in such when I try to run them permanently.
If you are trying to run a China clone ignition system you better get a spare and test it and carry it with you.
You will eventually need it.
 
Top