M-Tronic Problems Solved?

[ericm979]

So, am I correct that the temperature sensor is in the control module itself and the heat transferred through the crankcase wall is calculated ? And, higher RPM increases the energy produced and is somewhat inversely proportional to the solenoid opening so as the RPM drops more fuel is supplied ?

I wondered about that short jumper, but it tells the control module the position of the choke.

I would still like to know what that signal to the solenoid actually is, a varying DC voltage or a varying signal rate.
Not that it makes a ****.

Probably the sensor just measures the temp at the coil. That would be affected a lot by the incoming air temp as it's next to the fan that's bringing in outside air. So I think it's mostly measuring air temp. Which makes sense since that's what affects fuel/air mixture- warm air being less dense. Pretty much all car EFI systems have an intake air temp sensor.

There is probably some heat transfered from the engine through the cases so it'd be seeing a higher temp than just the intake air but that's ok as long as it still tracks the air temp.

Generally more fuel will be delivered as rpm rises. The engine needs a certain ratio of fuel to air, and more rpm means the engine is pumping more air.

Car EFI systems have a ton of maps programmed into them. When you use a tuner on the EFI you're changing some of the maps. At least from my quick read of the patent I didn't see anything about maps. It sounds like the system learns, and then just records what it was doing last. Which is why an Mtronic saw sometimes won't start if you shut it off right at the end of a cut. It's still got the values from how it was running rather than from idle. There needs to be some sort of set of beginning values so it will run the first time or after you do a reset.

 

[sean donato]

So, am I correct that the temperature sensor is in the control module itself and the heat transferred through the crankcase wall is calculated ? And, higher RPM increases the energy produced and is somewhat inversely proportional to the solenoid opening so as the RPM drops more fuel is supplied ?

I wondered about that short jumper, but it tells the control module the position of the choke.

I would still like to know what that signal to the solenoid actually is, a varying DC voltage or a varying signal rate.
Not that it makes a ****.

I'd assume some sort of pwm signal, but have no way of knowing. I supposed with a multi meter and an o-scope you could figure out most of it of you cared to.

Probably the sensor just measures the temp at the coil. That would be affected a lot by the incoming air temp as it's next to the fan that's bringing in outside air. So I think it's mostly measuring air temp. Which makes sense since that's what affects fuel/air mixture- warm air being less dense. Pretty much all car EFI systems have an intake air temp sensor.

There is probably some heat transfered from the engine through the cases so it'd be seeing a higher temp than just the intake air but that's ok as long as it still tracks the air temp.

Generally more fuel will be delivered as rpm rises. The engine needs a certain ratio of fuel to air, and more rpm means the engine is pumping more air.

Car EFI systems have a ton of maps programmed into them. When you use a tuner on the EFI you're changing some of the maps. At least from my quick read of the patent I didn't see anything about maps. It sounds like the system learns, and then just records what it was doing last. Which is why an Mtronic saw sometimes won't start if you shut it off right at the end of a cut. It's still got the values from how it was running rather than from idle. There needs to be some sort of set of beginning values so it will run the first time or after you do a reset.

The fuel, timing and boost maps for my diesel vw is a 15kb file. Much more complicated system then our saws. I'd wager mtronic has to have some base maps to work off of. Everything can "self learn" off of a base map. Never gave any thought to where the sensors were located. I assumed the temp and rpm were in the ignition module. I was pretty sure I've seen what I would call a throttle position sensor already, but that may have been a husqy. I guess it could make assumptions to throttle angle based on expected and actual rpm.
Anyway, beyond filling the memory bank with more useless Information I just don't see how it matters.

 

[oldbuzzard]

I am not a certified Stihl tech, never been to a class. And, don't know if they would even get in to it. But, I would be curious to know how the M Tronic works. I can repair them easy as anything else.

But, I would like to know what the signal is to the solenoid. Like does the voltage increase/decrease to open close the solenoid ? Is it a gradual opening or does the solenoid open and close at a varying rate depending on demand ? Is it DC ? How do they rectify it ?
How does the RPM talk to the ignition coil ? Where is this temperature sensor located ?


I have built some reasonable complicated circuit boards to control bias, time delays, step start circuits, solid state relay switching, that kind of thing.

So, just curious. Not that you need to know to repair one that has been dropped out of a tree or run over.

Ok let me pass on what I (think) I know about Mtronic and Autotune. First, like you, I’ve never been to a Stihl school, so anything I say may be incorrect. If anyone corrects me I am glad to have learned something.
I am however, a retired aircraft mechanic who also has LOTS of experience with electronics and electro-mechanical devices. Now I like to repair chainsaws as well as being a B Certified Sawyer By USFS. I have rebuilt maybe three dozen or so Mtronics and Husky Autotune saws so I know what they look like under the cover.
Aircraft carbs and jet engine fuel controls have DEVICES that sense and adjust the fuel flow for things like RPM, air density, temperature, etc - all the things Stihl and Husky say they compensate for. If you take a Stihl Mtronic or Husky Autotune saw apart you won’t see any sensors or devices. Let’s take a Stihl 261C and compare it with a standard carb 261. It has a different fly wheel, coil, wire harness, and carb. The “computer” is (as best as I can tell) all in the coil. The carb has the solenoid and a micro-switch on the choke shaft. There is no external device to measure anything else. The coil can count the RPMs and I assume senses the temp as well. It can’t tell octane, fuel/oil mixture, air leaks, or anything else. So how does it “compensate” for these things?
There is no idle adjust on any of these saws. On a 261C the high idle is, I think, set to be around 3900 RPM and regular idle around 2900. So let’s say when you start the saw it high idles at 3100 Rpm. The computer says “I am not idling fast enough, so I must be too rich or too lean. I will start adjusting the mixture by modulating the solenoid valve.” I believe it defaults to richen first. If it richens the mixture and the RPMs further drop, then it says ”wrong direction, I need to go lean”. It then has the solenoid lean the mixture until it overshoots 3900, then it adjust the mixture back towards lean, going back and forth until it gets where it wants. This is a very simplified explanation but you get the idea. The coil/computer has different algorithms it will use to tune the mixture in different operating circumstances. They will also tune in the cut. Husky seems to do a lot more tuning in the cut.
Start one of these saws, sit it down and watch the chain. You can see and hear the RPMs change while it tunes itself - just as if you were turning the needle jet on a standard carb.
Im pretty sure the solenoid is what I was taught “chopped DC”. When magnetized, the coil of a solenoid pulls the armature to move it against a return spring. You can design the solenoid so that by applying a digital chopped dc of varying frequency you can modulate it between full off/on or open/close.
This is where I see operators have the biggest problem with these saws - the saw remembers the mixture setting from the last time it ran. If operating conditions (altitude, temp, whatever) have changed much then YOU HAVE TO GIVE THE SAW A CHANCE TO RETUNE!! Different saws have slightly different procedures but I find letting them idle at high idle for a minute seems to work on them all.
We, being men, never read the instructions that come with the saws. When you fire the saw up you set it down and let it tune itself. If you fire it up and immediately start trying to use it the saw gets all confused unless conditions are close to the same as the last time it started. So once it “learns” it‘s setting it is probably good for the day. Next morning, however, let it idle when you first start up.
A couple of maintenance tips I have learned - ALWAYS have a spare solenoid for Stihls. The solenoids are interchangeable between models, so the same solenoid can be used 261/362/400/462. There are black ones (bad), white ones, and green ones. Cost last one I bought was about $45 with new orange fuel filter which you also want. All colors interchange fine in my experience, although I’ve heard some people argue that. The solenoid has multiple failure modes. If I’m having ANY trouble that seems carb related I put on a new solenoid before anything else. Nine out of ten times that will fix my Mtronics. They are technically simple to swap but have some tiny attaching parts so I wouldn’t advise trying your first one in the field. I always take the carb off although I think you could do it by just taking the carb loose enough to work on.
Husky Autotunes - I find them to be much more reliable as long as you do the idle in the morning. I don’t even know where the solenoid is on the Husky carb. BUT taking a Husky carb off is to me more of a pain and there is a BIG GOTTCHA - Husky Autotune carbs, unlike Stihl, have to be matched to the coil part number. Start mixing Husky carb and coils around and your saw will probably go bat-poop and require the dealer to straighten out the software.
I’m sure someone one will take issue with something I’ve said and that is fine. Husky and Stihl are both secretive about how these systems really work and I welcome anything anyone else can teach me.

 

[ZeroJunk]

Ok let me pass on what I (think) I know about Mtronic and Autotune. First, like you, I’ve never been to a Stihl school, so anything I say may be incorrect. If anyone corrects me I am glad to have learned something.
I am however, a retired aircraft mechanic who also has LOTS of experience with electronics and electro-mechanical devices. Now I like to repair chainsaws as well as being a B Certified Sawyer By USFS. I have rebuilt maybe three dozen or so Mtronics and Husky Autotune saws so I know what they look like under the cover.
Aircraft carbs and jet engine fuel controls have DEVICES that sense and adjust the fuel flow for things like RPM, air density, temperature, etc - all the things Stihl and Husky say they compensate for. If you take a Stihl Mtronic or Husky Autotune saw apart you won’t see any sensors or devices. Let’s take a Stihl 261C and compare it with a standard carb 261. It has a different fly wheel, coil, wire harness, and carb. The “computer” is (as best as I can tell) all in the coil. The carb has the solenoid and a micro-switch on the choke shaft. There is no external device to measure anything else. The coil can count the RPMs and I assume senses the temp as well. It can’t tell octane, fuel/oil mixture, air leaks, or anything else. So how does it “compensate” for these things?
There is no idle adjust on any of these saws. On a 261C the high idle is, I think, set to be around 3900 RPM and regular idle around 2900. So let’s say when you start the saw it high idles at 3100 Rpm. The computer says “I am not idling fast enough, so I must be too rich or too lean. I will start adjusting the mixture by modulating the solenoid valve.” I believe it defaults to richen first. If it richens the mixture and the RPMs further drop, then it says ”wrong direction, I need to go lean”. It then has the solenoid lean the mixture until it overshoots 3900, then it adjust the mixture back towards lean, going back and forth until it gets where it wants. This is a very simplified explanation but you get the idea. The coil/computer has different algorithms it will use to tune the mixture in different operating circumstances. They will also tune in the cut. Husky seems to do a lot more tuning in the cut.
Start one of these saws, sit it down and watch the chain. You can see and hear the RPMs change while it tunes itself - just as if you were turning the needle jet on a standard carb.
Im pretty sure the solenoid is what I was taught “chopped DC”. When magnetized, the coil of a solenoid pulls the armature to move it against a return spring. You can design the solenoid so that by applying a digital chopped dc of varying frequency you can modulate it between full off/on or open/close.
This is where I see operators have the biggest problem with these saws - the saw remembers the mixture setting from the last time it ran. If operating conditions (altitude, temp, whatever) have changed much then YOU HAVE TO GIVE THE SAW A CHANCE TO RETUNE!! Different saws have slightly different procedures but I find letting them idle at high idle for a minute seems to work on them all.
We, being men, never read the instructions that come with the saws. When you fire the saw up you set it down and let it tune itself. If you fire it up and immediately start trying to use it the saw gets all confused unless conditions are close to the same as the last time it started. So once it “learns” it‘s setting it is probably good for the day. Next morning, however, let it idle when you first start up.
A couple of maintenance tips I have learned - ALWAYS have a spare solenoid for Stihls. The solenoids are interchangeable between models, so the same solenoid can be used 261/362/400/462. There are black ones (bad), white ones, and green ones. Cost last one I bought was about $45 with new orange fuel filter which you also want. All colors interchange fine in my experience, although I’ve heard some people argue that. The solenoid has multiple failure modes. If I’m having ANY trouble that seems carb related I put on a new solenoid before anything else. Nine out of ten times that will fix my Mtronics. They are technically simple to swap but have some tiny attaching parts so I wouldn’t advise trying your first one in the field. I always take the carb off although I think you could do it by just taking the carb loose enough to work on.
Husky Autotunes - I find them to be much more reliable as long as you do the idle in the morning. I don’t even know where the solenoid is on the Husky carb. BUT taking a Husky carb off is to me more of a pain and there is a BIG GOTTCHA - Husky Autotune carbs, unlike Stihl, have to be matched to the coil part number. Start mixing Husky carb and coils around and your saw will probably go bat-poop and require the dealer to straighten out the software.
I’m sure someone one will take issue with something I’ve said and that is fine. Husky and Stihl are both secretive about how these systems really work and I welcome anything anyone else can teach me.

Very interesting post. All I work on is Stihl . What I have found is that the diagnostic program really doesn't tell you much of anything other than if the wiring harness has issues. So you can find a broken wire with it.
Usually the ones I have worked on will not idle properly in the triangle position. Chain turns continuously , and when you try and rev it up just leans out and cuts off.
Usually, if the saw will sit and idle sounding like it is going to flood out but not it is normal.

Not easy to put in to words, but you can tell when it is working correctly.

The last one I repaired was a MS462C
and the solenoid, module, and everything was fine.. the screen in the carb was stopped up with felt from some off brand filter that I'm sure they though was a good idea.

Usually it is the solenoid. But, I have chased them all the way to the ignition module losing it's programing or whatever.

As far as Stihls diagnostic program, they have a long way to go.

 

[ericm979]

The patent says that changing the fuel/air ratio (the obvious way to do it) takes too long for a result. They change the timing and use the results to detect if the cpu should adjust more lean or more rich. The timing change causes a different result if it's lean vs rich.

Of course just because it's in a patent doesn't mean that's how they did it in the first production unit or how it works now. But the patent's explanation of the timing change being better makes me think that's probably how they're doing it.

 

[oldbuzzard]

See, I learned something! I can buy that they use an algorithmic program like that. Would still have to ultimately change rich/lean though I would think. Using Stihl or Husky it seems like the idle reset just gets the mixture in the ball park, then it takes a few cuts to get it zeroed in. I’ve found they are both still a little cranky for a few minutes and may require a couple of restarts before they settle in.

 

[oldbuzzard]

Very interesting post. All I work on is Stihl . What I have found is that the diagnostic program really doesn't tell you much of anything other than if the wiring harness has issues. So you can find a broken wire with it.
Usually the ones I have worked on will not idle properly in the triangle position. Chain turns continuously , and when you try and rev it up just leans out and cuts off.
Usually, if the saw will sit and idle sounding like it is going to flood out but not it is normal.

Not easy to put in to words, but you can tell when it is working correctly.

The last one I repaired was a MS462C
and the solenoid, module, and everything was fine.. the screen in the carb was stopped up with felt from some off brand filter that I'm sure they though was a good idea.

Usually it is the solenoid. But, I have chased them all the way to the ignition module losing it's programing or whatever.

As far as Stihls diagnostic program, they have a long way to go.

How often do you find a broken wire? I’ve been screwing around with a 362C for a while that will fire up ok but then die as soon as you blip the throttle. I’ve replaced the solenoid and the entire carb assy but nothing changes. Ive been suspecting the wiring harness.

 

[ZeroJunk]

How often do you find a broken wire? I’ve been screwing around with a 362C for a while that will fire up ok but then die as soon as you blip the throttle. I’ve replaced the solenoid and the entire carb assy but nothing changes. Ive been suspecting the wiring harness.

I'm not sure if broken is the right word. But, one of our techs pulled his hair out over a running issue and as soon as he replaced the wiring harness it ran correctly. Could have benn a bad connection at one of the terminals from the factory. Who knows.

 

[oldbuzzard]

I’ve got a new coil to put in mine, just been too busy. I think the 362C has the same set up as a 261C - four wires plus spark plug wire coming off the coil. Kill Switch wiring works the same but two additional wires come off the coil and go to the solenoid. These two wires attach to the coil with spade lugs. The lugs on a 261C have a small screw to hold them tight. I’ve had a 261C that didn’t have that little screw and the spade lugs didn’t make a good connection giving erratic running of the saw.

 

[bwalker]

Ok let me pass on what I (think) I know about Mtronic and Autotune. First, like you, I’ve never been to a Stihl school, so anything I say may be incorrect. If anyone corrects me I am glad to have learned something.
I am however, a retired aircraft mechanic who also has LOTS of experience with electronics and electro-mechanical devices. Now I like to repair chainsaws as well as being a B Certified Sawyer By USFS. I have rebuilt maybe three dozen or so Mtronics and Husky Autotune saws so I know what they look like under the cover.
Aircraft carbs and jet engine fuel controls have DEVICES that sense and adjust the fuel flow for things like RPM, air density, temperature, etc - all the things Stihl and Husky say they compensate for. If you take a Stihl Mtronic or Husky Autotune saw apart you won’t see any sensors or devices. Let’s take a Stihl 261C and compare it with a standard carb 261. It has a different fly wheel, coil, wire harness, and carb. The “computer” is (as best as I can tell) all in the coil. The carb has the solenoid and a micro-switch on the choke shaft. There is no external device to measure anything else. The coil can count the RPMs and I assume senses the temp as well. It can’t tell octane, fuel/oil mixture, air leaks, or anything else. So how does it “compensate” for these things?
There is no idle adjust on any of these saws. On a 261C the high idle is, I think, set to be around 3900 RPM and regular idle around 2900. So let’s say when you start the saw it high idles at 3100 Rpm. The computer says “I am not idling fast enough, so I must be too rich or too lean. I will start adjusting the mixture by modulating the solenoid valve.” I believe it defaults to richen first. If it richens the mixture and the RPMs further drop, then it says ”wrong direction, I need to go lean”. It then has the solenoid lean the mixture until it overshoots 3900, then it adjust the mixture back towards lean, going back and forth until it gets where it wants. This is a very simplified explanation but you get the idea. The coil/computer has different algorithms it will use to tune the mixture in different operating circumstances. They will also tune in the cut. Husky seems to do a lot more tuning in the cut.
Start one of these saws, sit it down and watch the chain. You can see and hear the RPMs change while it tunes itself - just as if you were turning the needle jet on a standard carb.
Im pretty sure the solenoid is what I was taught “chopped DC”. When magnetized, the coil of a solenoid pulls the armature to move it against a return spring. You can design the solenoid so that by applying a digital chopped dc of varying frequency you can modulate it between full off/on or open/close.
This is where I see operators have the biggest problem with these saws - the saw remembers the mixture setting from the last time it ran. If operating conditions (altitude, temp, whatever) have changed much then YOU HAVE TO GIVE THE SAW A CHANCE TO RETUNE!! Different saws have slightly different procedures but I find letting them idle at high idle for a minute seems to work on them all.
We, being men, never read the instructions that come with the saws. When you fire the saw up you set it down and let it tune itself. If you fire it up and immediately start trying to use it the saw gets all confused unless conditions are close to the same as the last time it started. So once it “learns” it‘s setting it is probably good for the day. Next morning, however, let it idle when you first start up.
A couple of maintenance tips I have learned - ALWAYS have a spare solenoid for Stihls. The solenoids are interchangeable between models, so the same solenoid can be used 261/362/400/462. There are black ones (bad), white ones, and green ones. Cost last one I bought was about $45 with new orange fuel filter which you also want. All colors interchange fine in my experience, although I’ve heard some people argue that. The solenoid has multiple failure modes. If I’m having ANY trouble that seems carb related I put on a new solenoid before anything else. Nine out of ten times that will fix my Mtronics. They are technically simple to swap but have some tiny attaching parts so I wouldn’t advise trying your first one in the field. I always take the carb off although I think you could do it by just taking the carb loose enough to work on.
Husky Autotunes - I find them to be much more reliable as long as you do the idle in the morning. I don’t even know where the solenoid is on the Husky carb. BUT taking a Husky carb off is to me more of a pain and there is a BIG GOTTCHA - Husky Autotune carbs, unlike Stihl, have to be matched to the coil part number. Start mixing Husky carb and coils around and your saw will probably go bat-poop and require the dealer to straighten out the software.
I’m sure someone one will take issue with something I’ve said and that is fine. Husky and Stihl are both secretive about how these systems really work and I welcome anything anyone else can teach me.

Mtronic compensates for temp and oil ratio by sensing rpm and then comparing qith the standard map. Pretty simple.
Not as precise as a automotive system with MAF, TPS,02, etc, but more than good enough for a saw.
When the 562 first came out I did some testing running the standard 50:1 oil and switched to 24:1. The saw compensated and pulled the same rpm in and out of the wood.
I work in a industry that uses a insane amount of sensors, transmitters and controls. I have only a rudimentary idea of how it all works. The rest is PFM. AKA pure ****** magic. Mtronic in my way of thinking is no different. I accept it does what it does and how it gets there is of little difference.
Trouble shooting wise there is a coil, solenoid and simple wiring harness. That's it!

 

[Jza]

Mine seems to have straightened itself out just from using it now. Can you believe it?

I have a 661 that was like that. After about 6 tanks of fuel run thru it hard now it'll start 1 pull from cold after a 2 or 3 light pulls