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

[Cobby08]

Too fast of desired rpm from programming, add fuel, too low... yeah you guessed it. Monitors rpm, and throttle position. Idle is adjusted by timing primarily.

 

[MustangMike]

Mark, don't they also rev limit the M Tron saws by retarding the timing at a certain RPM (instead of a limited coil)?

 

[Cobby08]

I believe it’s a mixture of timing as well as richening it all to hell. Which makes sense as when I put the phunnie pipe on my 362 it had raw fuel galore in it.

 

[breese]

Unlike the auto world, this system seems (I am guessing until I dig into more) actually retards the timing as method of controlling the high end of RPM

 

[Mastermind]

Caught up again.

 

[VinceGU05]

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.

its a pretty cool system. i have seen my ported 441 get a run up on the system. tells you how starts and hours logged too. handy when i bought my 2nd hand 241. had 1hr 19 min run time on it

 

[VinceGU05]

I believe it’s a mixture of timing as well as richening it all to hell. Which makes sense as when I put the phunnie pipe on my 362 it had raw fuel galore in it.

and why they can keep up with ported saw needs and cover up bad air leaks. they seem to have great capacity to over fuel.

 

[retro]

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.

All diodes experience a voltage drop in-circuit. General usage (cheap) diodes drop between 1 to 1.5 volts when current flows through them. There are some slightly more expensive grades of diodes that will drop less than 1 volt when biased with current, but when describing the majority of them, about 1.5 v-drop is standard and expected... V-drop is easy to measure.

So, if a lower than nominal voltage on the solenoid causes it to enrich the mixture for cold starting, that would explain why a simple and cheap diode is being switched by the choke lever. If that is indeed what is being done there... a higher (than nominal) voltage sent thru the solenoid should lean the mixture, ya?

 

[retro]

@breese
In your opinion thus far, do you feel that the MT functions by varying a voltage sent to the solenoid or by data transmitter/receiver? Or utilizing both.., such as a LIN bus or a CAN bus? Are any of the leads twisted pair wiring?

EDIT: For monitoring and control duties LIN bus would be much cheaper than CAN bus and be more than fast enough.

 

[Duane(Pa)]

Great thread! I am a reader here, but I'm sure most of you know a wireless Fastach goes nuts at the top RPM. Leads me to believe there is something electrical going on in addition to over fueling for a high limit...

 

[breese]

So, if a lower than nominal voltage on the solenoid causes it to enrich the mixture for cold starting, that would explain why a simple and cheap diode is being switched by the choke lever. If that is indeed what is being done there... a higher (than nominal) voltage sent thru the solenoid should lean the mixture, ya?

Not sure.... I would think the reverse might be true... If a lower voltage (such as the saw is not running) causes it to run rich, then there is a greater possibility of flooding the saw.
Now if the lower voltage (or no voltage) was a lean or closed solenoid, there would be less or no fuel passing thru the carb.

In your opinion thus far, do you feel that the MT functions by varying a voltage sent to the solenoid or by data transmitter/receiver? Or utilizing both.., such as a LIN bus or a CAN bus? Are any of the leads twisted pair wiring?

I forgot about the LIN and CAN bus... I will have to look. thanks
None of the leads are twisted pair.. This is a single wire and a ground.

 

[breese]

Leads me to believe there is something electrical going on in addition to over fueling for a high limit...

Agreed.. Looking like the system retards the timing at the high end.

 

[retro]

Not sure.... I would think the reverse might be true... If a lower voltage (such as the saw is not running) causes it to run rich, then there is a greater possibility of flooding the saw.
Now if the lower voltage (or no voltage) was a lean or closed solenoid, there would be less or no fuel passing thru the carb.

The MT system doesn't flood the motor easily like a choke valved carb does. MT carbs allow the motor to start and run in the choke lever position (for over a minute to provide settings reset function) without pooling fuel in the crankcase. With cranking (and idling) RPMs being sensed along with temperature, combined with a signal/control voltage drop thru the diode providing starting enrichment would make sense, since diodes are commonly added to circuits to provide a predictable and precise voltage drop at lowest cost. This sort of strategy requires no feedback, so a data bus does not have to be functional yet (or exist) to provide solenoid position enrichment for cold starting and warmup. Engine RPMs monitoring and mechanical design limits inherent in the solenoid and layout of the fuel ports in the carb could allow the engineer a high level of precision and control.

Just been thinking out loud here... I don't think the MT is as complicated as some might think. Because it doesn't have to be.

I forgot about the LIN and CAN bus... I will have to look. thanks
None of the leads are twisted pair.. This is a single wire and a ground.

Thanks for clarifying. The MT system does not require a complete end-to-end data bus to exist to provide precise control, but if an asynchronous data bus exists to monitor its' only five possible slave (engine RPMs, ignition timing, mixture control solenoid, temperature, RTC clock) positions, it must certainly be a standard LIN bus network, since there is only one-wire available for powering each slave device.

 

[retro]

Agreed.. Looking like the system retards the timing at the high end.

I think @treemonkey (and others?) have verified exactly that by using a timing light to monitor ignition timing retard during testing? Makes complete sense anyway.

 

[breese]

The MT system does not require a complete end-to-end data bus to exist to provide precise control, but if an asynchronous data bus exists to monitor its' only five possible slave (engine RPMs, ignition timing, mixture control solenoid, temperature, RTC clock) positions, it must certainly be a standard LIN bus network, since there is only one-wire available for powering each slave device.

One of the newer 1 wire bus networks is by Maxim Integrated and that was the first one I went to before you reminded me about the other....

Until such time as I can figure out exactly what protocol, it will be hard to know....

I think @treemonkey (and others?) have verified exactly that by using a timing light to monitor ignition timing retard during testing? Makes complete sense anyway.

Yea.... Unlike an Auto RPM limiter (most notable by the sound as the ignition is basically turned off and back on), the ability to retard the timing give the saw and even power thru this period.

 

[backhoelover]

I would LOVE to get my hands on the Saw to Computer cable and the software... for starters.

Biggest questions I have:
What are the voltages across this data/power cable between the coil, carb, and any other component (its a little hard to get that info without a running saw... LOL ).
Any schematics available?

i have software. if i had a saw i would make a video for everyone

 

[backhoelover]

Mdg1 hardware

 

[backhoelover]

Ohm meter leads to check res

 

[breese]

I have been receiving and reading a lot of documentation that people have sent me (Thank You All).
What is interesting is there is a lot of talk about these (or some models) have a type of altimeter.
So far I have not located such a device and I cannot believe (but could be wrong) that it would be within the coil pack.... hmmmm

As of right now, things are slowing down on this project because I have not been able to get my hands on a (good or bad) mdg1 cable.
This cable is the key to gaining access to the saw's coil pack. Without it, I have to figure out the pins on the CPU and try to find out who made the CPU.
The parts within the sealed coil pack have no markings at all.

 

[Cobby08]

I have been receiving and reading a lot of documentation that people have sent me (Thank You All).
What is interesting is there is a lot of talk about these (or some models) have a type of altimeter.
So far I have not located such a device and I cannot believe (but could be wrong) that it would be within the coil pack.... hmmmm

As of right now, things are slowing down on this project because I have not been able to get my hands on a (good or bad) mdg1 cable.
This cable is the key to gaining access to the saw's coil pack. Without it, I have to figure out the pins on the CPU and try to find out who made the CPU.
The parts within the sealed coil pack have no markings at all.

I have not seen any proof of this either so my assumption is that when they are claiming 'm-tronic adjusts for dirty filters, altitude, fuel quality, etc' they are just assuring that using the same inputs (rpm, throttle position vs the desired tables in the controller) that it will compensate for all those factors. I know on a TS 500i they have a pressure sensor in the case but still wouldn't be able to determine a very accurate altitude. Just my thoughts...