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

[nohoff]

The rev range where the saw has the most hp.
Its around 9000-95000 rpms on a stock saw.

 

[tree monkey]

I'd like to gain control of the max timing advance to defeat built-in rev limiters. Other than that they work fine as is IMO.

a higher rpm before it starts to retard timing. 1000 rpm higher on the 661's, 500 or so on the 261's

 

[breese]

Next phase:
Now that I know where different components are located and an approximant depth, I will be using one of the other coils and begin milling down to the CPU.
Once I have access to the CPU and traces, it should be possible to reverse engineer the CPU and or find any markings indicating what chip it is...
The other side of this is it should also allow the coil to be powered up and tested for power and data lines.

As for some of the questions that have popped up:
Increased RPM might be a benefit but, finding an holding RPM within the best power range at WOT should produce a stronger saw within the cut....

Right now there are too many questions on what this actually does, how it does it, and just how much information does it store....
One thing I am positive of IF the documentation is right, there is a writable section within the chip or the software would not have Reset availability.

 

[Redbull661]

"reverse engineer the CPU" ...now that is bad ass!!!

 

[Brush Ape]

It would make more sense to me if that is actually a variable position plunger being pulled open (against a light return spring or not) by a small electromagnetic coil.

Would Pintle Valve be the 15 cent word here? (Split infinitves are highlighted in Stihl orange.)

 

[FergusonTO35]

I'm reading all this with interest. I was an auto mechanic for my first career, and the workings of the M-tronic system is more what I am used to than regular carbs. As much as I love my little 1955 tractor, there are times I would love to drop a modern EFI Toyota engine in place of the stone age Continental Z-134. One question: does the M-tronic system store power for the ECM in some way, or does the first pull on the starter cord power it up?

 

[breese]

One question: does the M-tronic system store power for the ECM in some way, or does the first pull on the starter cord power it up?

On the pull of the starter...
There is no power storage. The 2 capacitors I have located are not directly related / connected to the CPU.
The addition of a battery type power storage would have many downfalls one of them being the heat generated by the saw and the 2 power coils within the whole coil.

 

[CR888]

The promo info says MT is powered by dual pole magnets on the cooling fan or something like that. No battery from what I hear.

 

[breese]

This is going to be a very slow process but as you can see, I have found the chip...
Not sure if there will be any identifying markings but I hope to uncover it and the traces....
Fingers Crossed.

 

[FergusonTO35]

Glad to hear it doesn't need to store power. Hopefully, this technology will filter down to other pull start engines, maybe even see real fuel injection come about.

 

[blsnelling]

Glad to hear it doesn't need to store power. Hopefully, this technology will filter down to other pull start engines, maybe even see real fuel injection come about.[/QUOTE]
It's already here.

 

[MustangMike]

Likely the power is generated from under the flywheel, just like they do for heated handle saws.

 

[blsnelling]

Likely the power is generated from under the flywheel, just like they do for heated handle saws.

There's nothing under the flywheel.

 

[MustangMike]

OK, I was just guessin! Maybe it is generated right at the coil?

 

[Canadian farm boy]

Don't the Mtronic saws have 2 sets of magnets on the FWs?
1 set for spark and the other set to power the coil/ecu?

 

[blsnelling]

OK, I was just guessin! Maybe it is generated right at the coil?

As the song goes, "There's a whole lot of guessing going on," lol.

 

[tree monkey]

Don't the Mtronic saws have 2 sets of magnets on the FWs?
1 set for spark and the other set to power the coil/ecu?

yes, and the coil reads the polarity.

I believe that the fi system has a generator under the flywheel, mt does not

 

[VinceGU05]

should we be also hooking into a stihl concrete cutter to get up to speed with how the fuel injection system works on it?

 

[Redfin]

Don't the Mtronic saws have 2 sets of magnets on the FWs?
1 set for spark and the other set to power the coil/ecu?

yes, and the coil reads the polarity.

I believe that the fi system has a generator under the flywheel, mt does not

Polarity is reversed on magnet sets.

 

[breese]

I believe that the fi system has a generator under the flywheel, mt does not

The entire system is charged by way of the flywheel.
This is a Magneto type system. The magnets on the flywheel transfer energy to the pickups on the coil pack (this is why the spacing between the coil and flywheel must be very close).
Next the energy is transferred to the larger of the 2 coils within the coil pack.
From the lager internal coil, the energy (voltage) passes thru (in simple terms) to the smaller coil and the voltage is raised high enough to fire a spark plug (somewhere between 5 and 10 thousand volts the last time I checked).

As the flywheel rotates, and the piston hit TDC, there is another pickup on the coil pack that when triggered allows the coil pack to now Fire the sparkplug.

By modifying the key between the flywheel and crank, you are moving the trigger point that the second pickup is seeing, there-by resulting in the advancement of timing you are seeing in your other modified saw builds.

The M-Tronic has the ability (internally) to Delay or Advance the firing of the sparkplug as it monitors the second pickup and logically deciding when to fire.

Now, because the coil pack is storing energy (voltage) created by the Magneto, the M-Tronic coil (internally) uses some of this power to supply power for the built in logic. This is not new. All single unit electronic ignitions have been using part of the power for internal logic. The M-Tronic is just using more of it to supply power to external sensors, coils, etc....