Help me diagnose a MS201TC running issue please

[ZeroJunk]

I did too things. I took the carb back off and made sure the plastic coupler was seated in the index slot in the carb,

I did a pressure test on the fuel line and could not get it to hold. Now, the line is two piece and has a plastic elbow. So, it is obviously going to blow by that at some point. But, it should have held better than it did IMO.

Anyway, between checking the plastic piece in the manifold and replacing the fuel line the problem was solved. Or, at least I can't get it to cut off now.

Of course, it may work for the tree service an hour and start right back . Who knows.

But, I'm pretty sure that the saw was simply leaning out and the electronics were telling it to shut off. Doing it's job.

 

[backhoelover]

So if saw is running lean software will cut saw off?

 

[ZeroJunk]

So if saw is running lean software will cut saw off?

I don't know. I was thinking that it was since the saw was cutting off like a switch. But, I don't see that as a feature anywhere. So, maybe not.

 

[backhoelover]

They do need a MIL light on them in my Opinion

 

[Stihldoc]

M-Tronic won't shut a saw off if it goes too lean. Of course, the saw will eventually lose compression and skid to a stop. The only way M-Tronic will shut off a saw is because of a critical component failure- such as coil failure causing no spark. Newer controllers (ignition modules) are "locked". This means that the M-Tronic can't lean out the fuel trim lower than a programmed amount. The locked modules have all but emiminated M-Tronic tuning issues from taking down a saw. Mechanical issues such as air leaks or obstructed fuel flow will cause a lean run condition that M-Tronic can't correct. As I said in an earlier post on this topic, check for mechanical issues first.

 

[DND 9000]

This means that the M-Tronic can't lean out the fuel trim lower than a programmed amount.

Is there maybe a tech sheet availible how the range of the fuel values are for each chainsaw or power tools normally? A MS 661 C-M must have of course a higher fuel value (switching cycle of the solenoid valve) as a Ms 201 C-M because of the much higher displacement.

 

[Ketchup]

Stihldoc, when you say module, what part of the M-tronic components is this? I assume it is neither the coil or solenoid. Is it the other piece mounted on the carb?

It also sounds like an older M-tronic can supply very low fuel levels, but the symptoms of this behavior would be a poor performance before shutdown as opposed to a sudden full stop like a kill switch ground. I suspect something in the handle electric, as my saw was also dropped by the PO.

Zerojunk, what pressure did your fuel line fail at? Mine also seemed poorly sealed compared to other components. Did you remove the elbow when you replaced the line?

At least twice now I have taken my saw apart and tweaked details. Afterward it would run and seemed fixed. But then it dies in a super frustrating situation, typically 3/4 through a big removal in large horizontal cuts. Please let us know if this saw comes back to you.

 

[backhoelover]

Is there maybe a tech sheet availible how the range of the fuel values are for each chainsaw or power tools normally? A MS 661 C-M must have of course a higher fuel value (switching cycle of the solenoid valve) as a Ms 201 C-M because of the much higher displacement.

They don’t do that due to so many differences like
Altitude
Air quality
Temp
Fuel quality
Etc

 

[backhoelover]

Is there maybe a tech sheet availible how the range of the fuel values are for each chainsaw or power tools normally? A MS 661 C-M must have of course a higher fuel value (switching cycle of the solenoid valve) as a Ms 201 C-M because of the much higher displacement.

They give u a base numbers in tech video training. I’ll see if I can watch it and get the number for you

 

[DND 9000]

Ok, thank you very much for trying to find out the fuel value numbers. I really appreciate your help my friend.

 

[ZeroJunk]

Zerojunk, what pressure did your fuel line fail at?

It would not hold at even one squeeze, just jumping around. I know it was leaking around the elbow, but usually those hoses stick pretty tight around a fitting and have to be pried off if they have been on a while.
So, it could have been picking up some air there. And, the fitting may have been out of place behind the carb. I'll find out next week if it is working reliably. Wouldn't bet on it, but I'll keep my fingers crossed.

 

[ZeroJunk]

Well, the tech did the diagnostic test. Really didn't show anything useful. Stihl technical services said to check the condition of the piston and cylinder. Looked fine. The intake elbow was intact, no cracks.
So, the tech replaced the top handle, again. And, that fixed it. Those handles come with the wiring, or at least you can get them that way.
I felt from the start that this was an ignition issue. May have been wires shorting in one of the connectors. It was not on the switch end.
Anyhow, that's the story if anybody cares.

 

[Ketchup]

I care. My saw is at parts status because of a similar symptom. Unfortunately I already disassembled the entire handle assembly and found nothing visibly damaged. Wires are tough to diagnose though. I suspect the coil on mine, but now I'm not sure. I should know better than to buy a saw with a computer chip and a wiring harness...

Thanks for the follow up!

 

[ChuckYaUp]

I was facing this exact issue with a saw at my shop.

Would start and run perfectly fine but suddenly die in the middle of a cut. Sometimes it would cut fine then it wouldn't. I didnt think the coil itself was bad since it would act up hot or cold. plus it would start right back up every time. ended up noticing the handle was pressing against the crankcase when it was leaned forward and the wires were pushed between the two when cutting. found a wear spot in the red wire and it was grounding against the case. i put a piece of electrical tape between the wires and the case and the problem stopped. to double verify i wiggled a screwdriver around between the case and the wire and it shorted right out. Seems like it could be a common issue on these due to the placement of the wires maybe combined with a weakening AV system.

 

[Snik66]

I was facing this exact issue with a saw at my shop.

Would start and run perfectly fine but suddenly die in the middle of a cut. Sometimes it would cut fine then it wouldn't. I didnt think the coil itself was bad since it would act up hot or cold. plus it would start right back up every time. ended up noticing the handle was pressing against the crankcase when it was leaned forward and the wires were pushed between the two when cutting. found a wear spot in the red wire and it was grounding against the case. i put a piece of electrical tape between the wires and the case and the problem stopped. to double verify i wiggled a screwdriver around between the case and the wire and it shorted right out. Seems like it could be a common issue on these due to the placement of the wires maybe combined with a weakening AV system.

Had similar issue with my saw. Would fire up like instantly but die just as instantly. Would "pop" every time you start it but never really"start". Couldn't figure it out. Bought a new solenoid (have needed to purchase a few so far for this saw) didn't fix it, bought a new coil, found the broken wire while installing the new coil(because you have to take the entire friggin saw apart to change it). The wire that was broken was the red wire just like chuckya up said. Mine was broken and hidden behind perfectly good insulation so i couldn't see it. But pulling on it confirmed the wire was broken inside. (Continuity test would've caught that too). By the way, the wire harness was 21$to replace and not horrible to get in there. The coil was i think like 130$and was a giant pain in the ass to install... last bit of advice, this really thru me for a loop. When testing for spark, pull that thing HARD! I was having trouble verifying spark was present by spinning the engine over with an impact gun on the drive clutch nut. It wasn't spinning it fast enough! So it would spark "sometimes" just like when it had the broken wire in the handle. I brought my other 201 home and figured that one out! After hrs of scratching my head looking at a saw with a stiff neck...Thanks to all who comment on these. Really helps a brother out

 

[lone wolf]

Well have you tried cleaning the carb yet? Its worth a try at this point,but the acting up after it fell suggests something is sucking air maybe ? Did you vac test the whole thing yet?

 

[dolson5233]

MS201 M-Tronics are renown for failing fuel solenoids. Brad is right to suspect it because that is what the trouble often is. Stihl now has a solenoid valve test routine that should be performed in addition to pulling the data from the module. The fuel trim numbers will tell you what the module is doing to try to keep the motor running properly. The low fuel trim value is typically around 40-45. If you encounter a value down around 30, it tells you that the M-Tronic is cutting back fuel supply (or at least trying to) because it senses the motor is running too rich. Newer modules are "locked" at a minimum high fuel trim of 45. Anything below 45 on high trim is potentially problematic. Stihl has had quality issues with the solenoid valves- there is a new style coming out that is more durable. The M-Tronic diagnostic looks for electrical problems- it will not detect a mechanical problem. Often a mechanical problem will affect the fuel trim numbers and needs to be recognized as such. The new solenoid test looks for pressure leakage that is indicative of a failing solenoid. I don't say "failed" until it fails completely. These "failing" solenoids will leak a little fuel and cause running issues. A leaking solenoid will pass the M-Tronic electrical test, but will fail the new pressure test. If your saw has a solenoid issue, be sure you and your dealer know that the solenoid has a 3 year warranty because it is an emissions device.
M-Tronic is a very dependable engine management system, but it isn't foolproof. A mechanical problem will screw up an M-Tronic saw just like it'll do to a conventional carbureted saw. Has your dealer pulled the data off the module? It won't always tell you what the problem is, but it will help rule-in or rule-out problems. A troublesome tank vent will still cause the saw to die, M-Tronic or not. I'd take a good look at the wires within the handle- the post said that the owner had replaced the handle. The M-Tronic wires are small and delicate- they're easily damaged. I would also recommend putting a Stihl ZAT-4 spark tester on the unit and the M-Tronic testing side cover along with the bar and chain. Go cut with the saw and watch the spark. Does it disappear when the saw begins to die, or does it continue until the engine slows down to the electronic low cutoff RPM? Has anyone checked the fuel filter, fuel hose, and carb inlet screen? Any of these can cause a shutting off issue.
I work on 2 or 3 M-Tronic saws per day and I'm seeing fewer and fewer REAL M-Tronic problems. The new generation of locked modules have solved almost all of the lean running problems. I hope that the new ceramic? solenoid valves are more robust than what's out there right now. I'm an old guy who still uses my trusty 028WB on a weekly basis, but my 3 year old MS261 CMZ is starting to win me over. M-Tronic and other electronic engine management systems are going to be around for the foreseeable future. Adapt or die off. Thats the choice all us old dinosaurs face.

I purchased a 201 TCM in April. It has had running issues since day 1. I have taken it back to Ace Hardware, where I purchased it, over 4 times. I have also taken it to two other Still Shops. Every time I go out cutting firewood the saw starts, cuts for 3 or 4 cuts and then dies. And it continues throughout the day. In the first five wood cutting trips it had over 150 starts. Each time I take it to ACE about the problem I am told there is nothing wrong with it. I have owned 7 other Stills over the years and have never had a problem with any of them. This 201 is the most expensive saw I have purchased, but has been nothing but trouble. I have called Stihl tech Support and reported the problem. They just refer me to another dealer. Any assistance will be greatly appreciated.

 

[lone wolf]

I purchased a 201 TCM in April. It has had running issues since day 1. I have taken it back to Ace Hardware, where I purchased it, over 4 times. I have also taken it to two other Still Shops. Every time I go out cutting firewood the saw starts, cuts for 3 or 4 cuts and then dies. And it continues throughout the day. In the first five wood cutting trips it had over 150 starts. Each time I take it to ACE about the problem I am told there is nothing wrong with it. I have owned 7 other Stills over the years and have never had a problem with any of them. This 201 is the most expensive saw I have purchased, but has been nothing but trouble. I have called Stihl tech Support and reported the problem. They just refer me to another dealer. Any assistance will be greatly appreciated.

Try a new solenoid for the carb if no one did yet.

 

[lone wolf]

Well, the tech did the diagnostic test. Really didn't show anything useful. Stihl technical services said to check the condition of the piston and cylinder. Looked fine. The intake elbow was intact, no cracks.
So, the tech replaced the top handle, again. And, that fixed it. Those handles come with the wiring, or at least you can get them that way.
I felt from the start that this was an ignition issue. May have been wires shorting in one of the connectors. It was not on the switch end.
Anyhow, that's the story if anybody cares.

I have a 241 C here hat has a pinched wire, and it will run and then break up electrically. Well, at least I know what the problem is.

 

[ZeroJunk]

I have a 241 C here hat has a pinched wire, and it will run and then break up electrically. Well, at least I know what the problem is.

Just replaced the wiring harness on another MS201TCM last week. It is a tedious job. Much easier to just replace the complete top handle with the wiring harness included, just cost more.

I think I am up to four where it was the wiring, about the same where it was the solenoid, and one where it was the module.

Keep in mind, there is a lot more wiring to go wrong in a top handle.