261 M-Tronic - What makes it tick.....

[dustinwilt68]

#Dallisback

 

[Cracker Boy]

I remember when fuel injection in sutos first came out everyone hated it.now with software along with improvements in it.the throttle response along with hp gain is the best thing that happened oit tunes itself.my buddy has a 406 smallblock kept having fuel problems with caarb problems.the cam is so radical.we put aftermarket fuel injection on it and the car gained probably 30 hp and runs so much better.no more. Leaking secondary o rings no more blown power valves.to me this is allmost like a throttle body on a car.i tore my 261 m tron apart last night.

 

[breese]

i tore my 261 m tron apart last night.

What are you doing to it?
Anything related to this thread?

 

[breese]

I managed to uncover the chip and its connections to the board.
Applying 9v to the sensor connection shows there is a voltage regulator reducing the power to this (and I am betting) chip.

I am now contemplating purchasing the computer to saw adapter to find out what electronics are in it... I do not see anything within the coil assembly that strips the power and allows the software to communicate with the saw.

Does anyone have one of these cables?
I have some documentation indicating the cable does not directly connect to the computer thru the serial port or USB port but is a Bluetooth connection..

 

[nohoff]

Its a bluetooth adapter.
The first prototypes were USB but they had some problems.
You connect it between the Sparkplug and the Ignition coil and the first prototypes killed some USB Controllers on the mainboards.

 

[breese]

Interesting it has a connection to the sparkplug...
Not sure why when the Coil pack has knowledge of TDC and that can be used to timing.

Yea, I think I need to get my hands on one..... lol

 

[nohoff]

It connects to the ground through the spark plug and it reads the rpms throug it.
In the diagnostic runs it checks the Timing and the Voltage through this.
I should film a diagnostics run.

 

[RI Chevy]

I must admit, I am really digging this thread. [emoji106]
Awesome stuff here guys. Thanks for sharing all your work here.

Sent from my SM-G930V using Tapatalk

 

[Cracker Boy]

What are you doing to it?
Anything related to this thread?

Not really honestly she runs but im in process of rebuilding it needs new piston gonna put new seals.im trying to soak all this in and learn what you are doing very interesting thanx

 

[breese]

Right now (without a diagnostic tool) here is what I know and will also try to explain a few things.

As I said before, there are 2 sensors on the Coil pack that are spaced away from the fly wheel. One is the magnet coil that gets its energy / voltage (DC) from the magnet on the actual fly wheel... You can think of it in simple terms as a reverse alternator. Instead of the Rotor with windings spinning within the magnet pool, the magnets spin and the pickup gets the energy.

The second contact is a trigger that corresponds with TDC. If you pull the flywheel you will see a section with magnets and another smaller section that looks like it might be a magnet. This smaller one is what the coil pack uses to understand TDC.

Internally I have found the coil pack is extremely smart.
Each device that connects to the coil pack has a built in slave ID. So a carb might have a built in ID of #254, a temp sensor of #056 and a future sensor might have an ID #126.
Because of the hardcoded ID's the CPU will have knowledge of the device, what it is, how to communicate to it, and know how to use that information to best serve the saw.

The CPU/ECU has the ability to monitor multiple sensors and or devices. This explains how the Carb solenoid is able to open and close anywhere in the range of 0% to 100%.

What I do not understand (yet) is how it knows how much to open. At the moment I do not see a sensor telling the system what the current Airflow is.

My best guess is that my monitoring the RPM (also done thru the coil pack by using the TDC trigger), it makes small but very fast decisions on the amount of fuel to supply and reacts either increases or decreases fuel based on that RPM.

In Stihl's own words for WOT "The resulting engine speed pattern is analyzed by the microprocessor"

NOTE: There is a newer version that actually has a switch on the carb choke shutter for start detection.

Depending on the available commends within the CPU in the coil pack, it should be possible to add other sensors, devices, and change the programming and or device info so as to retrain / learn / or anything thru it.

The Diagnostic kit and its built in electronics is going to be the key.

I am still studying the CPU in the coil pack for more clues...

 

[MustangMike]

Thanks, I thought all along it was a little more complex than most people thought, the the temp sensor, which so many told me did not exist!

 

[nohoff]

All version have the starter detection switch.
Its just shorting the two wires

 

[breese]

Its just shorting the two wires

Normally I would agree... But in this case, we have both power (9v) and data going across the line.
Shorting this line would cause an all out short of both, there-by causing the 9V to short to ground and cause the coil pack to fail.

 

[breese]

Its just shorting the two wires

Ok... So inside the switch assembly is a diode.
There are different types of diodes and this one actually I need to look into.

When the Choke is turned on for starting, the mechanical switch diverts the power and data to thru the diode and carb solenoid there-by changing the value of the signal (data) and that change informs the CPU / coil pack that the saw is now in start mode.

 

[nohoff]

Dont know if the it was the ms261 oder MS 362 but one had 0 0hm at start position.
I ll take care of it tomorrow at work and try it at some new saws^^
MS201 - MS462 are all available for testing.


Early M-tronic Arctic versions had problems when the heating system was activated. They 4-stroked at WOT. We changed carbs/generators and everything was fine.

 

[breese]

Does anyone know of a dealer or repair place that has a dead or believed to be bad diagnostic cable?
The one that connects the computer to the saw....

 

[breese]

So I have managed to uncover the trace connections on the cpu (circled in red)
With 5v applied to the Diagnostics connections, I have been able to get a few reading off the traces.... Right now I am not in a position to figure out what each one is...

Some of the traces might be seen but there could still be a slight coating on them so I will have to take care in not screwing them up....

 

[Cracker Boy]

Does anyone know of a dealer or repair place that has a dead or believed to be bad diagnostic cable?
The one that connects the computer to the saw....

I will ask

 

[Adirondackstihl]

@Cobby08

 

[Cobby08]

Right now (without a diagnostic tool) here is what I know and will also try to explain a few things.

As I said before, there are 2 sensors on the Coil pack that are spaced away from the fly wheel. One is the magnet coil that gets its energy / voltage (DC) from the magnet on the actual fly wheel... You can think of it in simple terms as a reverse alternator. Instead of the Rotor with windings spinning within the magnet pool, the magnets spin and the pickup gets the energy.

The second contact is a trigger that corresponds with TDC. If you pull the flywheel you will see a section with magnets and another smaller section that looks like it might be a magnet. This smaller one is what the coil pack uses to understand TDC.

Internally I have found the coil pack is extremely smart.
Each device that connects to the coil pack has a built in slave ID. So a carb might have a built in ID of #254, a temp sensor of #056 and a future sensor might have an ID #126.
Because of the hardcoded ID's the CPU will have knowledge of the device, what it is, how to communicate to it, and know how to use that information to best serve the saw.

The CPU/ECU has the ability to monitor multiple sensors and or devices. This explains how the Carb solenoid is able to open and close anywhere in the range of 0% to 100%.

What I do not understand (yet) is how it knows how much to open. At the moment I do not see a sensor telling the system what the current Airflow is.

My best guess is that my monitoring the RPM (also done thru the coil pack by using the TDC trigger), it makes small but very fast decisions on the amount of fuel to supply and reacts either increases or decreases fuel based on that RPM.

In Stihl's own words for WOT "The resulting engine speed pattern is analyzed by the microprocessor"

NOTE: There is a newer version that actually has a switch on the carb choke shutter for start detection.

Depending on the available commends within the CPU in the coil pack, it should be possible to add other sensors, devices, and change the programming and or device info so as to retrain / learn / or anything thru it.

The Diagnostic kit and its built in electronics is going to be the key.

I am still studying the CPU in the coil pack for more clues...

There ya go...