Stihl Electronic Ignition - Gets Stuck In Full Advance?

[SteveSr]

Hello,

I have noticed an issue with my vintage 1993 034 Super when starting it. It will either start easily or try to rip the fingers off your hand or your hand off your wrist!

This morning it was probably in the upper 30s or low 40s during the first cold start. It pulled over so hard that I thought that it might be hydro locked. I don't remember this happening before. So I pulled the plug out and it was dry. Put everything back together and finally got it to start.

I was working at a local county charity firewood cutting workday so had a lot of warm starts and restarts. Sometimes it seemed that the spark advance was stuck on. Every pull would try to yank your fingers off. Last time I turned the switch off to make sure that it wasn't my arm and pulled it over without problems. Next pull I flipped the switch on and it started up easy with one pull without trying to pull my hand off.

So have any of you ever noticed this behavior on any of the early Still electronic ignitions?

 

[Old2stroke]

That sounds like the kind of gremlin that can show up in electronic circuits, annoying intermittent faults that can't be chased down until full failure. The electronics don't actually do the advance, the coil is positioned relative to the FW and piston TDC to give max advance (just like old points magnetos) and what the electronic package does is ****** the ignition from this max setting to give easier starting without recoil kickback, so when the electronics starts to go funny, it's possible that the ****** function could be the first to go and the ignition would go back to an advance of close to 30 deg BTDC. Electronic systems are great until they fail and there is no good way to predict the lifetime of a semiconductor. You DON'T want to know how dependent your car is on electronic systems, only good thing is the auto manufactures have spent more money and use many mil spec semiconductors, be nice if chainsaws were treated the same way.

 

[pioneerguy600]

Hello,

I have noticed an issue with my vintage 1993 034 Super when starting it. It will either start easily or try to rip the fingers off your hand or your hand off your wrist!

This morning it was probably in the upper 30s or low 40s during the first cold start. It pulled over so hard that I thought that it might be hydro locked. I don't remember this happening before. So I pulled the plug out and it was dry. Put everything back together and finally got it to start.

I was working at a local county charity firewood cutting workday so had a lot of warm starts and restarts. Sometimes it seemed that the spark advance was stuck on. Every pull would try to yank your fingers off. Last time I turned the switch off to make sure that it wasn't my arm and pulled it over without problems. Next pull I flipped the switch on and it started up easy with one pull without trying to pull my hand off.

So have any of you ever noticed this behavior on any of the early Still electronic ignitions?

I have an early flat top 066 that has done this for the past 5 or so years. The saw was a special build I did back many years ago when building hot saws on here was all the rage, anyway the coil worked properly for the first 5 years or so but eventually lost it ability to r e t a r d the timing. Starting the saw will test ones strength and patience..

 

[pioneerguy600]

I now see the site has blocked the word r e t a r d from being used on here.

 

[ZeroJunk]

I have an early flat top 066 that has done this for the past 5 or so years. The saw was a special build I did back many years ago when building hot saws on here was all the rage, anyway the coil worked properly for the first 5 years or so but eventually lost it ability to r e t a r d the timing. Starting the saw will test ones strength and patience..

I did not think that vintage even had the banned word at no RPM . Thought they were just a dumb coil, like 25 or so all the time.

 

[pioneerguy600]

I did not think that vintage even had the banned word at no RPM . Thought they were just a dumb coil, like 25 or so all the time.

Not a vintage module, remember its a built saw not stock.

 

[sean donato]

Saws coils have had automatic timing adjustment for a lot of years now. It's not surprising if something in the 0xx series has this issue. Replace the coil and move on with life.

 

[SteveSr]

That sounds like the kind of gremlin that can show up in electronic circuits, annoying intermittent faults that can't be chased down until full failure. The electronics don't actually do the advance, the coil is positioned relative to the FW and piston TDC to give max advance (just like old points magnetos) and what the electronic package does is ****** the ignition from this max setting to give easier starting without recoil kickback, so when the electronics starts to go funny, it's possible that the ****** function could be the first to go and the ignition would go back to an advance of close to 30 deg BTDC. Electronic systems are great until they fail and there is no good way to predict the lifetime of a semiconductor. You DON'T want to know how dependent your car is on electronic systems, only good thing is the auto manufactures have spent more money and use many mil spec semiconductors, be nice if chainsaws were treated the same way.

Oh, I am well aware of the electronics involved having spent a career as an embedded systems electronics engineer.

I am not sure that is a prelude to eventual failure or just some design quirk that just shows up periodically under certain conditions. It appears that it can be reset by pulling the saw over with the ignition off. This is effectively what I did when I removed the plug to check for hydro lock. Put it back together and it started right up!

As for cars... Most probably have between 25-50 embedded processor in it. The big problem is not hardware issues but crappy/buggy software. They finally proved that Toyota's unintentional accelleration issue was likely NOT caused by floor mats but by a particular software bug. Here are some references if you want to investigate further.

https://www.ganssle.com/rants/toyotasexpensivesoftware.html

 

[SteveSr]

I did not think that vintage even had the banned word at no RPM . Thought they were just a dumb coil, like 25 or so all the time.

At some poiont Stihl started using a PIC processor in its ignition coils to set the timing advance curve. I suspect that 1993 was too early for this coil to be one of those. Probably had some analog circuitry like a MOSFET switch which could provide a memory function.

 

[ZeroJunk]

At some poiont Stihl started using a PIC processor in its ignition coils to set the timing advance curve. I suspect that 1993 was too early for this coil to be one of those. Probably had some analog circuitry like a MOSFET switch which could provide a memory function.

I was thinking, which is dangerous, that if it started with a zero it likely had a "dumb" coil.
I know that the old 064's, 046's etc, never seemed to have a banned word( BTW another reason to leave this forum) at start. They would jerk the rope quite harshly if you got lazy.

In the repair world. Some of the newer Stihl weed eaters loose the ability to advance. Will not take the fuel. And, you would swear it is a carb issue. But, it is the ignition staying around zero.

 

[SteveSr]

In the repair world. Some of the newer Stihl weed eaters loose the ability to advance. Will not take the fuel. And, you would swear it is a carb issue. But, it is the ignition staying around zero.

Which model(s) are showing this symptom? 4-mix or regular 2-stroke?

 

[SteveSr]

I did some research in my IPL archive and apparently the 034/S went through some different coil part numbers in its lifetime.

It started life as:
1125-400-1300

And later changed to:
0000-400-1300
Which is the "generic" coil part number that is used on LOTS of different Stihl saws.

I also found reference to the processor controlled ignition modules starting about the year 2000 so if mine is original it may be fixed timing or a defect that is causing it to fire early and it appears to do it on the first revolution of the crank. My hand is always close to the recoil when it tries to rip my hand off.

 

[ZeroJunk]

Which model(s) are showing this symptom? 4-mix or regular 2-stroke?

I had it on a BR700 last week. You know that coil is $125 ???? It was firing all over the place.

But, I'm thinking it was mostly FS85's where I would swap the carb and then have to replace the ignition.

I don't remember changing a coil on a 4 mix weed eater. But, my memory is pretty suspect.