Stihl ms 661 cm mtronic has no spark!

[Chevboy0167]

Any flat spots on the wires looks suspect according to your picture. Looks like they have been pinched against another component. Small fragile wires can tear and have a break or intermittent connection.

A continuity test with a multimeter and giggle wires to confirm good or bad.

 

[Lee192233]

The circled spots are suspect. It's probably not worth it for you but I always apply this to low current/highly sensitive sensor connections at work. It's about $75 for 20 ml but it goes a long ways. It's called Stabilant 22a.

 

[newworld]

ms661c mtronic.

if no spark how do you diagnose if its the control ignition module or the solenoid valve?

i guess it could also be wiring harness...but how do you eliminate between the 2 main causes?

 

[lone wolf]

ms661c mtronic.

if no spark how do you diagnose if its the control ignition module or the solenoid valve?

i guess it could also be wiring harness...but how do you eliminate between the 2 main causes?

Check the wiring harness wires for an open circuit with an Ohm Meter.

 

[stihltech]

Most under diagnosed part of any electrical system. Connections and wiring. Nothing else will work without them. And don't forget grounds.
Juice has to get to a part and have a path out.

 

[PV Hiker]

Might check the carb if the solenoid is even getting fuel to it. If the solenoid is not seeing fuel then the computer will not spark.

You replaced the carb to suspect solenoid and wiring. Go further and check carb also.

To edit to add, leave carb on and put suspected solenoid on. Try different combinations.

 

[newworld]

so it follows then if you are getting fuel to the carb and your spark plug is wet but no spark it could be then either wiring or ignition module failure....

 

[sawmill sam]

Check the wiring harness wires for an open circuit with an Ohm Meter.

Success! Put the saw back together after cleaning the contacts with brakleen and checking wires with an ohmmeter and she fired right up.
No obvious dirt or grime around the carb contacts but that's what was wrong.
I'll be ready for it next time it happens!
Thanks for the help guys!!

 

[sawmill sam]

Any contacts that you touched, disconnected, or jiggled are suspect including the connector at the solenoid (that white thing on the carb).

Unless you are using canned gas (Motomix, Trufuel or equivalent) ALSWAYS drain and run dry. This is how saws come from the factory and can sit on the shelf for YEARS but always start right up. Even non-e pump gas looses the cooling volatiles over time as well as octane rating which the already lean M-tronic-strato saws don't like. Old gas is a good way to burn up a saw!

Don't confuse a fuel problem with a flaky electrical connection. Don't quote me but I think that the solenoids are like 35 ohms. Put your meter on the harness and start wiggling connections.

Steve, you, and a few others were absolutely right about the electrical contacts being at fault. A little brakleen and careful reassembly and I'm good to
go! Thanks to everyone for the tips about mtronics, they really are a different animal

 

[SteveSr]

Might check the carb if the solenoid is even getting fuel to it. If the solenoid is not seeing fuel then the computer will not spark.

Not true! Computer could care less about fuel all it wants to see is an electrical connection to the solenoid before providing spark. The system has NO fuel sensor.

 

[SteveSr]

so it follows then if you are getting fuel to the carb and your spark plug is wet but no spark it could be then either wiring or ignition module failure....

Fuel flow is irrelevant for spark.

 

[SteveSr]

This brings up an interesting thought... Oil makes a great electrical insulator. This is what keeps utility transformers from shorting out. 2-stroke oil is just as good an insulator so if it manages to get into the connectors you have the makings for an intermittent / open connection.

So if you have an oil film in your connector and put your saw in storage for a while after several hundred temperature cycles (while in storage) the oil has penetrated the connection creating an open circuit.

 

[PV Hiker]

Not true! Computer could care less about fuel all it wants to see is an electrical connection to the solenoid before providing spark. The system has NO fuel sensor.

Thanks for the catch Steve! Should not have been multi tasking with way too many distractions. Cheers....