ms261c-m mtronic issue

[Everett Phillipston]

ok, here we go;
I’ve searched thru and read a bunch about the ignition coil, mtronic carb reset, etc. here’s what I did...

1) New wiring harness from coil to carb servo connection- old one had two yellow & red wires cut. New Wires look good.
2) gapped flywheel with a business card...made sure the “key” was lined up with notch in crank spline
3) checked and cleaned ignition “point” surfaces
4) checked all contact surfaces on switch for cold start, run, & stop. Everything looks kosher
5) took muffler off and visually inspected piston and cylinder. Looks good.
6) saw idles in cold start. Let it go for 2 minutes for mtronic reset/calibration
7) saw will not rev/climb ...bogs out, catches itself and resumed idle if I don’t force the issue. If I do, stalls.
8) wont restart. Let it cool, will idle at cold start.

Suspected diagnosis: bad ignition module-won’t function at temp.
Tell me I’m wrong, and why.

Many thanks!

 

[PV Hiker]

Just a couple of more checks.... Fuel filter and Air cleaner good and clean?

 

[Everett Phillipston]

Just a couple of more checks.... Fuel filter and Air cleaner good and clean?

Yes sir.

 

[Gypo Logger]

For a relatively new saw it should be something simple. Possibly a plug issue. Owning three of them all I know is that there’s some great technology under the hood.

 

[Iceboy]

I think you should change the solenoid valve.

 

[stihl86]

Since it runs in cold start for 2 minutes, it might not be the solenoid. But on the other hand, it could be. The joys of a electronically controlled fuel system.
Just make sure the ex screen isn't clogged, I've never seen one clog on a Mtronic. But its possible.
And don't forget the saw uses a very conventual carburetor which is susceptible to dirt.
Rule out the fuel delivery system before looking at the module.
Either way, module should carry a two year warranty. Just for info.

 

[anymanusa]

For a relatively new saw it should be something simple. Possibly a plug issue. Owning three of them all I know is that there’s some great technology under the hood.

He said wires were cut. I don't think it's a new saw.

 

[Everett Phillipston]

He said wires were cut. I don't think it's a new saw.

Correct; wires from ignition to carb were cut just before the ignition side white clip which mates to the carb solenoid harness white clip. I replaced the entire ignition side harness with a quality used part.

 

[Sepia]

Why were the wires cut?

 

[Everett Phillipston]

Why were the wires cut?

No clue. I bought the saw as a project. No tank/handle, need wiring harness, and an mount for tank.

 

[Sepia]

Any chance the carb boot got damaged/cut?

 

[Everett Phillipston]

Any chance the carb boot got damaged/cut?

Interesting. I’m breaking it down again now as we go back and forth. I’ll take a closer look, but it looked good before

 

[Everett Phillipston]

Carb boot is good

 

[Sepia]

Any pinched or kinked lines? Tank vent okay? I am thinking fuel starvation so doing the simple checks. Also, change/swap the spark plug and check the lead to eliminate another simple possibility.

 

[Everett Phillipston]

Any pinched or kinked lines? Tank vent okay? I am thinking fuel starvation so doing the simple checks. Also, change/swap the spark plug and check the lead to eliminate another simple possibility.

Lines are good. Ample fuel delivery to carb. No vapor lock....tank vent is good.

 

[Sepia]

If you suspect ignition module is failing once hot, check for spark at plug when you get a no start situation. After that, I would do a pressure/vacuum test if you have the tools. Also, check condition of plug when saw quits: wet? dry? color?

 

[Everett Phillipston]

If you suspect ignition module is failing once hot, check for spark at plug when you get a no start situation. After that, I would do a pressure/vacuum test if you have the tools. Also, check condition of plug when saw quits: wet? dry? color?

What is the purpose of pressure vacuum test at this stage? Plug is wet. Even when saw fires, it is impossible to see spark when plug is grounded to cylinder. I tried it in a dark room and could not verify spark; put the plug back in for ***** n giggles, went out and it fired up.

 

[Sepia]

I assume your plug is gapped correctly - likely .020" but don't take my word for it. Try a different plug and see if you still can't see spark - you should be able to see it quite easily in a moderately dark room. Wet plug says you are getting plenty of fuel and you have good compression I assume - that leaves ignition.

Purpose of pressure/vac test is to eliminate the possibility of an air leak somewhere. If you have the tools it is a free test and is better than using the Magic Eight Ball diagnostic tool

 

[Everett Phillipston]

I assume your plug is gapped correctly - likely .020" but don't take my word for it. Try a different plug and see if you still can't see spark - you should be able to see it quite easily in a moderately dark room. Wet plug says you are getting plenty of fuel and you have good compression I assume - that leaves ignition.

Purpose of pressure/vac test is to eliminate the possibility of an air leak somewhere. If you have the tools it is a free test and is better than using the Magic Eight Ball diagnostic tool

Compression is a healthy 170. FYI

 

[Everett Phillipston]

I assume your plug is gapped correctly - likely .020" but don't take my word for it. Try a different plug and see if you still can't see spark - you should be able to see it quite easily in a moderately dark room. Wet plug says you are getting plenty of fuel and you have good compression I assume - that leaves ignition.

Purpose of pressure/vac test is to eliminate the possibility of an air leak somewhere. If you have the tools it is a free test and is better than using the Magic Eight Ball diagnostic tool

Can you recommend a good vac test gauge? I have a compression tester already. Vacuum test I would assume is aka a leak down test?