MS261 Stalling/Not idling M-Tronic Issue?

[luke...]

Ive got a MS261 (2021) thats started to not idle, starts ok from cold, run it through some cuts and put it down and itll cut out after 10 seconds or so

It was due a service so has had fuel filter, air filter and spark plug

Some googling seemed to point similar issues at the fuel solenoid, so ive just replaced that but still got the same issues

I tried an M-Tronic reset thinking that was needed after the new solenoid, following the process for m-tronic 3.0 but it wont idle on cold start for longer than 13 seconds, guide says to leave it running between 30-60 seconds but everytime, itll idle, get to 10 seconds the idle will raise the it'll cut out each time

Anyone had anything similiar?

Cheers in advance

 

[Colonel428]

Ive got a MS261 (2021) thats started to not idle, starts ok from cold, run it through some cuts and put it down and itll cut out after 10 seconds or so

It was due a service so has had fuel filter, air filter and spark plug

Some googling seemed to point similar issues at the fuel solenoid, so ive just replaced that but still got the same issues

I tried an M-Tronic reset thinking that was needed after the new solenoid, following the process for m-tronic 3.0 but it wont idle on cold start for longer than 13 seconds, guide says to leave it running between 30-60 seconds but everytime, itll idle, get to 10 seconds the idle will raise the it'll cut out each time

Anyone had anything similiar?

Cheers in advance

Hi Luke. I've got a 500i and it would act the same way as yours. Started fine and ran well in the cut but when I would set it down it would idle for about 10 seconds, rev up and die. The gentleman who ported my saw said to dump the fuel in the tank and run canned premix gas thru it. I did it and it seemed to clear up the problem. Evidently the gas evaporating messes with the m- tronics. Course if you already used canned mix everything I've suggested is useless...lol. Steve.

 

[Bruiser1]

Try some seafoam I've had great luck with that

 

[stihltech]

Fuel is always the first thing to look at. 3/4 of the saws that come in the shop have water in the fuel.
If replacing the solenoid, clean the carburetor and verify the inlet lever also.
A full diagnosis is called for.
I will admit, that solenoid was the most likely suspect. Now you need to go farther.

 

[bwalker]

Fuel is always the first thing to look at. 3/4 of the saws that come in the shop have water in the fuel.
If replacing the solenoid, clean the carburetor and verify the inlet lever also.
A full diagnosis is called for.
I will admit, that solenoid was the most likely suspect. Now you need to go farther.

Yes.
Start at the start. Mtronic is just an additional solenoid so you check the things you would on a old school saw first.

 

[DTLMG]

Had one doing the same exact thing. Stihl Tech hooked it up to the computer replaced ignition coil works great now. I assume the microprocessor in the ignition coil was bad and was not talking to the carb at idle

 

[bwalker]

Had one doing the same exact thing. Stihl Tech hooked it up to the computer replaced ignition coil works great now. I assume the microprocessor in the ignition coil was bad and was not talking to the carb at idle

That's funny it was the coil. My 400c ate a coil too. Never had a Stihl saw prior to this eat a coil.

 

[ZeroJunk]

A guy dissected one of those Mtronic coils. Lot of tiny surface mount components to go bad. As opposed to an inductor, capacitor, and trigger.

 

[epo]

A guy dissected one of those Mtronic coils. Lot of tiny surface mount components to go bad. As opposed to an inductor, capacitor, and trigger.

It doesn't have to be M-Tronic or AutoTune to have such components inside, and it has been for very many years.

https://www.arboristsite.com/threads/ms460-clone-no-spark.374071/post-8241035

 

[ZeroJunk]

It doesn't have to be M-Tronic or AutoTune to have such components inside, and it has been for very many years.

https://www.arboristsite.com/threads/ms460-clone-no-spark.374071/post-8241035

The only thing added was advance, or retard depending on how you look at it, for starting ease.
As opposed to "dumb" coils.

Mtronic, and fuel injection are a quantum leap in complexity.

 

[epo]

The only thing added was advance, or retard depending on how you look at it, for starting ease.
As opposed to "dumb" coils.

Mtronic, and fuel injection are a quantum leap in complexity.

Regardless of what functions they perform, and I'll vouch that the ones you've listed are only part of the functions they perform, they must have a microcontroller and a few more ICs with the surface mount technology you mentioned as some unique feature of M-Tronic. Did you actually follow the link?

 

[bwalker]

The only thing added was advance, or retard depending on how you look at it, for starting ease.
As opposed to "dumb" coils.

Mtronic, and fuel injection are a quantum leap in complexity.

"Quantam" leap is a stretch. Mtronic equiped machines are still dead simple.

 

[ZeroJunk]

They have memory. An EPROM. They lean the fuel out almost instantaneously and increase or decrease the fuel according to how the saw reacts. They have a thermometer, although the particular Stihl training video I watched didn't say exactly what it did.

The new Stihl weed eaters and blowers have a circuit board of a sort that you can see.

Once in a blue moon they will stay in the time retarded mode, probably top dead center.
And, you will think it is a carb issue because it won't "take the gas".

 

[bwalker]

They have memory. An EPROM. They lean the fuel out almost instantaneously and increase or decrease the fuel according to how the saw reacts. They have a thermometer, although the particular Stihl training video I watched didn't say exactly what it did.

The new Stihl weed eaters and blowers have a circuit board of a sort that you can see.

Once in a blue moon they will stay in the time retarded mode, probably top dead center.
And, you will think it is a carb issue because it won't "take the gas".

I don't believe mtronic uses any sensor inputs besides rpm. If it did use other sensor inputs a thermometer woukd be used to compensate for differences in air density that track temperature.

 

[epo]

I don't believe mtronic uses any sensor inputs besides rpm. If it did use other sensor inputs a thermometer woukd be used to compensate for differences in air density that track temperature.

STIHL M-Tronic™ Engine Check :

 

[bwalker]

STIHL M-Tronic™ Engine Check :

View attachment 1177190

There you go.

 

[oldbuzzard]

Temp sensor has to be built in to coil which makes sense.
Testing of Flywheel - WTF? I can’t imagine what could go wrong with a flywheel unless it lost its magnetism. I have seen that once or twice on non-chainsaw magnetos that were stored somewhere in a strong magnetic field, but very rare.

 

[DTLMG]

Temp sensor has to be built in to coil which makes sense.
Testing of Flywheel - WTF? I can’t imagine what could go wrong with a flywheel unless it lost its magnetism. I have seen that once or twice on non-chainsaw magnetos that were stored somewhere in a strong magnetic field, but very rare.

The other option besides losing magnetism ( which I have never seen in 40 plus years) with flywheel would be to see if the key was sheared, We kind of got off the OP original question why it wouldn’t idle. I would also do a vacuum/pressure test on it to rule out any leaks. Did you recalibrate after installing solenoid? Depending on the serial number you may be able to do it manually or you may have to have Stihl tech connect to software to recalibrate it

 

[ZeroJunk]

I don't believe mtronic uses any sensor inputs besides rpm. If it did use other sensor inputs a thermometer woukd be used to compensate for differences in air density that track temperature.

Theory of operation says. According to Stihl. They react to a lean condition introduced instantaneously and adjust fuel load accordingly. I know there is no such thing as instantaneously, but faster than you will notice in use.

Not addressing temperature , but reaction to producing a lean condition and interpreting the reaction of the RPM.

They will shut down if they reach a temperature threshold. But, I don't think that is involved in determining the fuel load.

 

[ZeroJunk]

STIHL M-Tronic™ Engine Check :

View attachment 1177190

When it will not run that flies out the window.