# testing ignition module



## roundhead (Mar 28, 2012)

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


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## Karl Robbers (Mar 28, 2012)

roundhead said:


> 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.


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## ndlawrence (Mar 28, 2012)

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.


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## roundhead (Mar 28, 2012)

ndlawrence said:


> 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.


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## ndlawrence (Mar 28, 2012)

roundhead said:


> 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.


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## Old Fart (Mar 24, 2016)

Karl Robbers said:


> 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.


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## Old Fart (Mar 24, 2016)

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


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## hotshot (Mar 24, 2016)

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.


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## Old Fart (Mar 24, 2016)

hotshot said:


> 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.
> ...



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


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## SteveSr (Mar 24, 2016)

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.


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## backhoelover (Mar 24, 2016)

new coil on stihl can be tested. here the catch has to be 2000 and newer and you have the have the mdg tester.


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## rd35 (Mar 25, 2016)

Wow, this is my kind of thread. I just learned some real cool stuff. Thanks to all!


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## Okie (Mar 25, 2016)

rd35 said:


> 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.


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## SteveSr (Mar 25, 2016)

SteveSr said:


> 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.


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## backhoelover (Mar 25, 2016)

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.


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## Termite (Mar 25, 2016)

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.


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## SteveSr (Mar 25, 2016)

Termite said:


> 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.


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.


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## Okie (Mar 26, 2016)

SteveSr said:


> 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.


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## a. palmer jr. (Mar 26, 2016)

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.


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## Okie (Mar 27, 2016)

a. palmer jr. said:


> 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.


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## rickwil (Jan 10, 2021)

Okie said:


> 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.


I have been having problems with a Stihl BR600, no spark. I have tried several coils. I made a jig out of an old magneto and crankshaft that will spin the magnetic flywheel close to a properly gapped coil. All of the tested coils (2 new, 1 old) will not produce spark until about 300 rpm. which makes the blower impossible to stat by hand or run at low speeds. Do you know the possible reason? I am quite familiar with electronics, electrician, power engineer, and hd mechanic (retired) but this has me stumped.


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## purdyite (Jan 10, 2021)

Had a saw that wouldn't start--tested with the neon spark tester and spark seemed fine. HOWEVER--after some examination, I found that the porcelain sleeve around the electrode on the plug was broken at the base and was shorting the plug--it fooled the spark tester. I turned the plug upside down and noticed that the gap had disappeared! The porcelain sleeve had slid down to the gap. Shaking the plug, I heard a clicking sound as the sleeve was moving back and forth. Pretty sure spark plugs shouldn't make noise when you shake 'em.


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## rickwil (Jan 10, 2021)

purdyite said:


> Had a saw that wouldn't start--tested with the neon spark tester and spark seemed fine. HOWEVER--after some examination, I found that the porcelain sleeve around the electrode on the plug was broken at the base and was shorting the plug--it fooled the spark tester. I turned the plug upside down and noticed that the gap had disappeared! The porcelain sleeve had slid down to the gap. Shaking the plug, I heard a clicking sound as the sleeve was moving back and forth. Pretty sure spark plugs shouldn't make noise when you shake 'em.


I tried with new spark plugs still the same. I'll try to give the engine the fastest pull that I can, I guess.


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## a. palmer jr. (Jan 10, 2021)

I usually don't have any problem testing the Stihl modules, I just replace them with a known good one. With other brands it's not so easy to do...


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## rickwil (Jan 10, 2021)

a. palmer jr. said:


> I usually don't have any problem testing the Stihl modules, I just replace them with a known good one. With other brands it's not so easy to do...


Problem is that I have tried 2 new ones (Chinese made) but in the past have not had problems with the Chinese ones in other blowers.


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## a. palmer jr. (Jan 10, 2021)

Yeah, I usually just work on chainsaws but I know that not all the new ones are good but is it possible something is wrong with the flywheel? Sometimes when you shear the key it will still have spark but it will be at the wrong time.


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## cscltd (Jan 10, 2021)

rickwil said:


> I have been having problems with a Stihl BR600, no spark. I have tried several coils. I made a jig out of an old magneto and crankshaft that will spin the magnetic flywheel close to a properly gapped coil. All of the tested coils (2 new, 1 old) will not produce spark until about 300 rpm. which makes the blower impossible to stat by hand or run at low speeds. Do you know the possible reason? I am quite familiar with electronics, electrician, power engineer, and hd mechanic (retired) but this has me stumped.


Most modern electronic modules will not light up at 300rpm, in fact no small engine will run at 300rpm, even your “HD engine” idles over 300rpm i think , br600 idles around 2800 rpm, thus if you get spark at 300rpm and no start, you may have another issue or an non Oem module not working correctly


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## KASH (Jan 11, 2021)

Pioneer 600 in good tune will idle at 450 rpm all day long.I watched several shows on testing old outboard motors lots of these idle at 300 no problem.I thought that ignition problems were a thing of the past when electronic ignition came out.It turns out if your saw gets to be a few years old it"s pretty well assured your piece of junk coil will fail and your SOL because it is NLA.
The beauty of points file them many a couple of times during the 2000 or so hour life time of the chain saw.
When you check for spark with points you just turn the crank with your hand hand and watch and hear that healthy bright blue spark jump the 3/16 gap to ground.
Kash


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## Old2stroke (Jan 11, 2021)

rickwil said:


> I have been having problems with a Stihl BR600, no spark. I have tried several coils. I made a jig out of an old magneto and crankshaft that will spin the magnetic flywheel close to a properly gapped coil. All of the tested coils (2 new, 1 old) will not produce spark until about 300 rpm. which makes the blower impossible to stat by hand or run at low speeds. Do you know the possible reason? I am quite familiar with electronics, electrician, power engineer, and hd mechanic (retired) but this has me stumped.


For every ignition module there is a minimum velocity of the magnets sweeping past the coil pieces that will induce enough energy in the primary to allow the circuitry to work.


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## Old2stroke (Jan 11, 2021)

We are constantly getting questions about testing coils with an ohm meter and, as stated above, due to the electronic package that switches the primary, there is NO relevant test you can perform that will determine if the coil is faulty or not. The coil is an auto transformer and that means that the primary and secondary both have the same ground (connected internally to the coil legs) and it MUST be securely connected to the cylinder, so the only good test you can do with an ohm meter is verify this connection and you can do this by measuring the resistance between the plug end of the high tension lead and the cylinder. It should be the value of the secondary ( about 5 Kohms), if it is a lot higher it could be a bad connection at the end of the lead or high resistance between the coil legs and its mounts.


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## rickwil (Jan 11, 2021)

cscltd said:


> Most modern electronic modules will not light up at 300rpm, in fact no small engine will run at 300rpm, even your “HD engine” idles over 300rpm i think , br600 idles around 2800 rpm, thus if you get spark at 300rpm and no start, you may have another issue or an non Oem module not working correctly


It may be the Chinese module that I installed. Not sure about the actual RPMs I was spinning it, just a guess but it seemed fairly fast. Give it another go today.


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