MS661 -- No Spark

[PogoInTheWoods]

Passes all tests in the shop manual including micro switch diode test. Wiring continuity passes everywhere. Latest greatest 'D' ECU (coil). New plug (have tried several). Carb and solenoid are used OEM replacements from another saw.
Harness is new. No MDG available for further analysis. (The area dealer's unit went belly up -- imagine that.) Have read everything in the SM related to the ignition, but haven't seen whether or not a bad solenoid would create a condition where the coil would not provide spark. Have also not found a workaround spark test for the ECU anywhere in the absence of the MDG unit. Don't want to risk jumping around the solenoid/micro switch and maybe damaging the ECU somehow.

Would be grateful for any experienced input or enlightenment.

Thanks.

 

[Deleted member 117362]

Have only seen it once on a husky, but are your flywheel magnets strong?

 

[alexcagle]

Look for a bare wire from the generator.
Chafing from vibration can cause the rubber wire coating to wear through.
Sounds like the dealer needs to do an update, and is too lazy, or doesn't want to take the time to hook it up to the internet.

 

[PogoInTheWoods]

No generator. All wiring has been tested fine according to the methods recommended in the shop manual. This is a rebuild of what was a perfectly running 2 year old saw that suffered some rear handle/air box crash damage.

Question is whether a bad solenoid can cause a no spark condition.

 

[alexcagle]

Go to a different dealer?

 

[PogoInTheWoods]

He's the only one in my area I'd even take a saw to for diagnostics, let alone work on one of mine. His unit went belly up and he's waiting on Stihl for a remedy. Can't tell me one way or another if a bad solenoid could somehow cause a no spark condition. Has never seen it before.

Sorta why I asked the question here.

 

[DND 9000]

Question is whether a bad solenoid can cause a no spark condition.

Yes that can be, from my understanding. Here is what I found in the m-tronic TI of the MS 441:

Plug connection to control unit

A reliable connection must be ensured for communication between control unit, switching device and solenoid valve. If communication between control unit and solenoid valve is interrupted or faulty, the control unit does not initiate an ignition spark. Thus if there is no ignition spark, first check the plug connections and wiring harness between control device and solenoid.

Maybe this helps you to figure out the problem.

Also important: Do not perform the solenoid switch test with the 9V battery. This can destroy the control unit.

 

[PogoInTheWoods]

Sebastian! Thank you for the response. Was going to look through the 441 and 362 service manuals next to see if there was anything there addressing the question. I don't think I have access to the TI you referenced, though it appears that the wiring between the solenoid and the control unit is what's being addressed, not the solenoid unit itself. If by 'solenoid switch' you are referring to the micro switch, I went by the book for the diode test and the open test and both checked fine according to the parameters provided. Would seem like I'm back to the harness (new) and connections until I can either replace the solenoid or am able to find another dealer with a working MDG 1 setup..., who won't insist that I leave the saw and then take their word for what the diagnostics did or didn't reveal a couple o' weeks and 150 bux later.

Really hafta wonder what Stihl thinks a customer with a M-tronic problem who lives a hundred miles away from a dealer is supposed to do ..., if the dealer even has a competent tech with an MDG 1 setup that actually works in the first place. Sheesh.

 

[Captain Bruce]

I would like to learn how this issue was resolved. I also have the issue. Running engine, serviced some broken A/V mounts, from a log rolling onto the unit. Saw ran fine. Now its back together, and suddenly, no spark. Are there any links for "testing" the ignition coil, referred to as the control unit. How about the micro switch. I audibly clicks......but is is closing the circuit.....? etc. Any help is appreciated.

 

[Wood Doctor]

Stihl says to replace the ignition module if there is no spark. Most of the time the plug is not the problem. Here's a quote from the Stihl MS 661 service manual "A new ignition module must be installed if no ignition spark is obtained after checking that wiring and stop switch are in good condition."

 

[stihl86]

I would like to learn how this issue was resolved. I also have the issue. Running engine, serviced some broken A/V mounts, from a log rolling onto the unit. Saw ran fine. Now its back together, and suddenly, no spark. Are there any links for "testing" the ignition coil, referred to as the control unit. How about the micro switch. I audibly clicks......but is is closing the circuit.....? etc. Any help is appreciated.

It gets tricky trying to test the harness. If theres a terminal and/or wire problem, you may never catch it.
Best place to start is replace the harness. The system must be intact to operate.
The harness isn’t that expensive and at least you’ll know for sure.
The wires are like thread and easily broken after a mishap.

 

[Tom82]

So what coil do you have? There is 5 or 6 different coils. Also, what solenoid do you have? There is a black and a white solenoid. Some coils can only operate one of the two coils.

Stihl has come out with a repair kit that's an update for the 661. It's a coil, a solenoid, and a fuel filter. No need to program or anything else, just install the new parts and go.

 

[Captain Bruce]

To be clearer, after replace the lower and upper a/v mounts, and clutch cover, the saw started and ran for a short time....only because it was tested. It sat for a week, and when picked back up, no spark. I err on the side of caution, so I presume the wiring is okay. It is flooding/blow fuel out the carb.......as I try to start test for spark with a tester.....so I again presume the solenoid and miroswitch are functioning......the lead from the coil to the plug boot test ok. Swapping the ignition coil is the easiest and quickest method, so I think thats my next step.

As to TOM82, I have no idea which coil I have until I remove it. Ditto with the solenoid. Not sure what " some coils can only operate some coils??
Repair kit part #?

 

[PogoInTheWoods]

Double check your harness routing and check for appropriate continuity with a meter where you can before throwing in the towel. In my particular case, the ECM (coil) was replaced as was the solenoid, but I'm guessing the coil was still good and the solenoid was bad -- possibly damaged by me trying to troubleshoot things with little M-tronic experience at the time. Go ahead and check for spark by grounding the plug against the cylinder. You have little to lose by using that method even though I've heard it can damage the ECM. Frankly, I don't know what possible electrical difference there is between the plug being grounded outside the plug hole vs, screwed into it.

 

[Captain Bruce]

So, now I find my need to add, that I am a 30 Yr. licensed, small engine mechanic. I am able to test for spark, without being instructed. The wiring harness is quite complicated in terms of tearing the entire carb out, as well as the ignition coil, referred to as the control unit. I was hoping for a direct, "this is what to do response." Maybe nobody reading this has any experience with the M-tronic system? I'm not sure what "routing" refers to, as the wiring has never been removed. Appropriate continuity is an ohm meter, and zero resistance. Nothing has been "tested", given that the engine fired right up, and ran strong, after some simple repairs. Sat a week. Seems it has forgot how to start.....

The solenoid? As described in the manual, triggered by a mico-switch, on full choke, allows fuel to flow.....and fuel is definitely flowing. Its flooding the cylinder with every pull on the recoil.......just waiting for spark.
ALL spark testing is done with a tester grounded to the block, and plugged into the spark lead. No spark plug in the block. There's is zero difference between plug in and plug out. Just easier to pull the recoil to look for spark to begin with....

What is the generator behind the flywheel? The flywheel magnets had a yellowish glaze.......which was cleaned off slightly......its a new unit, so I figured thats some sort of coating pre-operation.

I greatly appreciate the forum folks who chime in because its simply part of their daily routine. Thats typing and reading. I'm a mechanic. I would never spend time looking for someone elses troubles, but you , the members of this forum, can be assured when this issue is resolved, I will detail everything involved; the next guy looking for a simple answer, to a simple problem, will be enchanted......

Double check your harness routing and check for appropriate continuity with a meter where you can before throwing in the towel. In my particular case, the ECM (coil) was replaced as was the solenoid, but I'm guessing the coil was still good and the solenoid was bad -- possibly damaged by me trying to troubleshoot things with little M-tronic experience at the time. Go ahead and check for spark by grounding the plug against the cylinder. You have little to lose by using that method even though I've heard it can damage the ECM. Frankly, I don't know what possible electrical difference there is between the plug being grounded outside the plug hole vs, screwed into it.

 

[Captain Bruce]

Have only seen it once on a husky, but are your flywheel magnets strong?

??????? Strong???

 

[Captain Bruce]

It gets tricky trying to test the harness. If theres a terminal and/or wire problem, you may never catch it.
Best place to start is replace the harness. The system must be intact to operate.
The harness isn’t that expensive and at least you’ll know for sure.
The wires are like thread and easily broken after a mishap.

Makes sense....maybe a bad connection.....I'll buy a coil, the harness, and return what I don't need....

 

[rupedoggy]

@Jacob J. could you help this guy? He seems like me. Pretty good on mechanical but the flow of electrons is somewhat of a mystery.

 

[Captain Bruce]

Yes that can be, from my understanding. Here is what I found in the m-tronic TI of the MS 441:

Plug connection to control unit

A reliable connection must be ensured for communication between control unit, switching device and solenoid valve. If communication between control unit and solenoid valve is interrupted or faulty, the control unit does not initiate an ignition spark. Thus if there is no ignition spark, first check the plug connections and wiring harness between control device and solenoid.

Maybe this helps you to figure out the problem.

Also important: Do not perform the solenoid switch test with the 9V battery. This can destroy the control unit.

What is the "test" to begin with? Why is a 9-V battery involved? What is Plug Conn. to c. unit? The small black plug? Its clean and tight....9V battery? Thats for a clock radio??

 

[stihl86]

Makes sense....maybe a bad connection.....I'll buy a coil, the harness, and return what I don't need....

Who’s going to take back a module that you used for test? Just curious.
You can do whatever you like. A bad connection can give a spark for one revolution and no more.
Chances are you going to miss it without an in-line tester. But have at it.
Removing the carb is not a major undertaking. Not at all.