Ms261c no ignition

[SteveSr]

A multi meter probe won't go in the connectors. So, you have to find a little piece of wire or something to stick in the hole.

Be VERY careful here that you don't deform the contacts in the connector and create an intermittent or open circuit. Nothing should be plugged into the connector that is any larger than the mating pin in the other half of the same connector.

And, if you are holding it with your fingers you are also reading the resistance across your fingers which is real and could be anything.

Skin resistance is in the hundreds of Kohms to many megohms and will not affect the reading on lower resistance circuits like we have here. However if you do happen to have a meter that auto-ranges it could cause some frustration.

 

[SteveSr]

It's an early model btw.

Well, you didn't tell us this in the beginning. Please post a photo of the ignition coil/control unit so that we know the part number. Also post a photo of the silver engine family tag that is located on the handle of the saw.

Some of the earlier M-tronics did have some issues but these have been fixed in subsequent revisions. However, they still mostly ran. One of the biggest issues is to let the saw idle for 30 seconds or so before shutting it down. This cools off the saw and lets the computer stabilize on the correct conditions for a restart. Once the engine stops there is no power to the computer.

 

[ZeroJunk]

Be VERY careful here that you don't deform the contacts in the connector and create an intermittent or open circuit. Nothing should be plugged into the connector that is any larger than the mating pin in the other half of the same connector.


Skin resistance is in the hundreds of Kohms to many megohms and will not affect the reading on lower resistance circuits like we have here. However if you do happen to have a meter that auto-ranges it could cause some frustration.

Here is a 10,000 watt 10 through 160 amplifier I built from scratch.

 

[oldbuzzard]

Hello. I'm the operations manager/mechanic for a commercial landscaping company. Have an ms261c that started for a split second and died. No ignition. Coil tests 25ohms. Did standard ignition coil testing procedures. Continuity on wiring is good. Crankcase checks. Brand new plug of course. Stihl dealer technician specifically told me that a faulty or failing fuel solenoid will not cut off ignition. I don't want to put a $150 coil on this saw and have it not start. I'm not an expert mechanic by any means. I'm just the guy at our shop who knows the most so maintenance and repairs to fleet and equipment typically fall on me. that knows the most.... Any help would be appreciated. I absolutely hate the mtronic. Never have an issue repairing any other 2 or 4 stroke engines.

I have repaired/rebuilt many, many 261Cs, and a number of 362Cs. I work on them more than any other saws. Mtronic and Autotune saws are good saws, you just have to trouble shoot them differently.
First off, if the saw has a black solenoid on the carb, throw it away and replace it with a white or green one and also buy a spare. Also be sure to put the orange fuel filter on the saw. Nine times out of ten that fixes a starting problem on Mtronic.
I have never seen that little solenoid “kill the spark”, but I’m not saying it couldn’t happen. I have never seen the ignition coil just quit on a 261C, but again, it could happen.
Look at the bottom of the ignition coil where the two wires from the coil to the carb attach. There is a small screw that holds it tight. I have seen that be loose and give you the symptom you are having.
It sounds like you know how to ring out the wire harness with an ohmmeter. Just remember, if you have an intermittent connection in the harness, you may make the connection “good” when you take a connector loose to check it.
Also, are you real sure it isn’t a carb or gas problem? My experience with 261Cs is that the spark is almost impossible to see unless you are in a dark room.
Every time I fixed a “weird” starting problem on those saws it ended up being something simple.

 

[sapponetta]

I have repaired/rebuilt many, many 261Cs, and a number of 362Cs. I work on them more than any other saws. Mtronic and Autotune saws are good saws, you just have to trouble shoot them differently.
First off, if the saw has a black solenoid on the carb, throw it away and replace it with a white or green one and also buy a spare. Also be sure to put the orange fuel filter on the saw. Nine times out of ten that fixes a starting problem on Mtronic.
I have never seen that little solenoid “kill the spark”, but I’m not saying it couldn’t happen. I have never seen the ignition coil just quit on a 261C, but again, it could happen.
Look at the bottom of the ignition coil where the two wires from the coil to the carb attach. There is a small screw that holds it tight. I have seen that be loose and give you the symptom you are having.
It sounds like you know how to ring out the wire harness with an ohmmeter. Just remember, if you have an intermittent connection in the harness, you may make the connection “good” when you take a connector loose to check it.
Also, are you real sure it isn’t a carb or gas problem? My experience with 261Cs is that the spark is almost impossible to see unless you are in a dark room.
Every time I fixed a “weird” starting problem on those saws it ended up being something simple.

 

[sapponetta]

Yea Im 100% positive there is no ignition. Excellent point about making connections on the harness while testing. And yes that is exactly how the harness runs. People were posting incorrect info on here. But at the end of the day, there is absolutely nothing that would stop a good coil from producing a spark on one of these besides air gap, flywheel, lead or spark plug. I'm going to look at the saw today, do a few things i forgot to do like test the HT lead, the spring is intact, and makes a positive feeling connection.... I will probably remove the harness completely and test it just because this saw has made me silly. But I don't see how it would cause the coil to not fire. It's just sending a duty cycle reference to the solenoid. It's not drawing power, getting a trigger form it, or anything else. This system is as simple as it gets. I guess I'm just apprehensive about replacing the coil when I have 22yo pieces of equipment sitting here and have never had a Stihl coil go bad. If it wasn't a $150 coil, and someone else's money,(and part of my budget bonus lol) I wouldn't care.

Thanks to everyone for their advice and the couple of good points made. I appreciate it. Happy holidays to everyone.

 

[PV Hiker]

If you remove the harness and testing it, it is a good idea to flex the wires around to see if a short opens up. Good luck

 

[SteveSr]

Here is a 10,000 watt 10 through 160 amplifier I built from scratch.

Cool! What do you need a 10KW amplifier for? Is this 10KHz-160KHz VLF communications? Are you talking to submarines?

 

[SteveSr]

Yea Im 100% positive there is no ignition. Excellent point about making connections on the harness while testing. And yes that is exactly how the harness runs. People were posting incorrect info on here. But at the end of the day, there is absolutely nothing that would stop a good coil from producing a spark on one of these besides air gap, flywheel, lead or spark plug.

I think that you are missing the point... The ignition module in an M-tronic saw is NOT just your standard self contained ignition coil. Think of it as an ECU (engine Control Unit) for a chainsaw. It is a microcontroller (computer) with the advanced capabilities of diagnosing the system connected to it. If the diagnostics detect a problem it kills the spark.

 

[sapponetta]

I think that you are missing the point... The ignition module in an M-tronic saw is NOT just your standard self contained ignition coil. Think of it as an ECU (engine Control Unit) for a chainsaw. It is a microcontroller (computer) with the advanced capabilities of diagnosing the system connected to it. If the diagnostics detect a problem it kills the spark.

How does it kill the spark with nothing wired to it? That's not how these coils work. This coil has a signal output that you don't have an a standard coil. No extra inputs. If the solenoid could kill the coil it would be wired to where the kill switch is. engine control unit is a generous term. I believe sends an rpm signal to the solenoid which is its duty cycle reference. And that's it. Someone correct me if I'm wrong, but this is about as advanced a control scheme as the EGR valve on a 1989 Toyota.

 

[ZeroJunk]

The question which I don't have an answer for is if you disconnect the little connector on the front of the coil will the coil still fire.

I don't know, but I suspect not.

It would be cool to see a schematic of the inside of the coil.

 

[ZeroJunk]

Cool! What do you need a 10KW amplifier for? Is this 10KHz-160KHz VLF communications? Are you talking to submarines?

It's an amateur radio amplifier. HF bands being 160 through 10 megahertz. Don't need 10 KW , but I had the tube.
Bought the plate transformer which is 6500 volts rectified from EPD in Wendell. Your neck of the woods.

 

[SteveSr]

How does it kill the spark with nothing wired to it? That's not how these coils work. This coil has a signal output that you don't have an a standard coil. No extra inputs. If the solenoid could kill the coil it would be wired to where the kill switch is. engine control unit is a generous term. I believe sends an rpm signal to the solenoid which is its duty cycle reference. And that's it. Someone correct me if I'm wrong, but this is about as advanced a control scheme as the EGR valve on a 1989 Toyota.

Since you are so sure how this works you should have little trouble fixing your saw.
HAND!

 

[L34]

How does it kill the spark with nothing wired to it? That's not how these coils work. This coil has a signal output that you don't have an a standard coil. No extra inputs. If the solenoid could kill the coil it would be wired to where the kill switch is. engine control unit is a generous term. I believe sends an rpm signal to the solenoid which is its duty cycle reference. And that's it. Someone correct me if I'm wrong, but this is about as advanced a control scheme as the EGR valve on a 1989 Toyota.

Believe me after working on my
441c
If the coil doesnt "see" the solenoid it will kill spark.
Someone prove me wrong if I am.
1c

 

[PV Hiker]

As you pull the starter cord the RPMs increase and the Chip comes alive and does a quick diagnosis. If it sees a bad fuel cylinder, or any shorts in the wiring (no feedback confirmation) it does not bother sparking.

If all is ok then the Chip delivers the same fuel, adjustment and spark as how the saw was running when it was shut down as a starting point.

Cheers,

 

[farmhard]

Ohms doesn't mean squat, it just means you have continuity. V=IxR. Resistance under load changes things.
Stop pulling your hair out and change the $21 part. Your time wasted is more than the cost of the part. Your hourly rate is costing the company more. If you have to back probe and diag, it is worth opening the cannon.
My thoughts on that coil is it should work with the wires disconnected and you put a second one on already.

 

[farmhard]

Believe me after working on my
441c
If the coil doesnt "see" the solenoid it will kill spark.
Someone prove me wrong if I am.
1c

I believe it to be an issue when the solenoid is stuck in the closed position which grounds the coil, I believe yellow wire on that one? I'd be disconnecting the wires at coil, then solenoid and retest each.

 

[sapponetta]

The question which I don't have an answer for is if you disconnect the little connector on the front of the coil will the coil still fire.

I don't know, but I suspect not.

It would be cool to see a schematic of the inside of the coil.

According 2 Stihl techs and 1 Stihl tech here yes. I trust them more than a forum poster who has obviously never even held a motronic in their hands. Which is obvious based on statements and questions they asked.....

 

[sapponetta]

Took the plunge, Fired right up with new coil. What do you know.....

 

[oldbuzzard]

Good for you, helpful info for the rest of us.