Stihl 088 Ignition Timing Issues

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Interesting. It likely is something like that, but I wonder what the signal is initially derived from? As an analog circuit designer that kind of thing interests me. No doubt they'll want it to be cheap and it does not have to be super accurate. I would probably try to create a fixed-width pulse off the ignition trigger and then rectify and average that. Then you could threshold detect and use that to shut off the spark. Then again, how you limit the ignition is probably important, and I don't know how they do that. Progressively skipping ignition pulses would seem to be the gentilest way, but I don't know what they do.

If you put a real small cap as a feed thru to limit the growing pulse. (increasing the rpm does increase the size).... to a rectifier circuit you then get a growing voltage relatively proportional to the rpm. A lot like an electronic tach.
once the voltage(rpm) gets to the trip point you shut off the primary with the normally conducting transistor. after it misses 2 or 3 ignitions the saw will slow down and refire and cycle on-off in rapid succession. If I can peel one open, I might be able to figure out how it works. :hmm3grin2orange:
 
The saw was all original......

Any idea if there was ever any change in the saws performance such as hard starting or became a screamer overnight all of a sudden? Or was it completely unchanged. I could see a scenario in electronics were a component goes bad and you get a very different reaction to a sine wave trigger causing a new mode of operating at a different time. been there done that.....:rock:
However I don't know how simple or complicated these things are.
 
Any idea if there was ever any change in the saws performance such as hard starting or became a screamer overnight all of a sudden? Or was it completely unchanged. I could see a scenario in electronics were a component goes bad and you get a very different reaction to a sine wave trigger causing a new mode of operating at a different time. been there done that.....:rock:
However I don't know how simple or complicated these things are.

The owner just told me it had gotten very hard to start.
 
On some stihl models you can watch the tach go down to about half of actual rpm when the module limiter kicks in. The rpm isn't changing that much, just the module not firing.
 
If you put a real small cap as a feed thru to limit the growing pulse. (increasing the rpm does increase the size).... to a rectifier circuit you then get a growing voltage relatively proportional to the rpm. A lot like an electronic tach.
once the voltage(rpm) gets to the trip point you shut off the primary with the normally conducting transistor. after it misses 2 or 3 ignitions the saw will slow down and refire and cycle on-off in rapid succession. If I can peel one open, I might be able to figure out how it works. :hmm3grin2orange:

I know this is old, but have you reverse-engineered any chainsaw ignition modules yet? I am in the process of de-potting an EM unit now.

Perhaps a hard rev limiter that cuts off spark at a particular RPM is not necessary. I have been looking at some advance curves and I was
surprised to find that the ignition advance # goes down somewhat at max RPM.
 
2 stroke retards the ignition at high rpm and a 4 stroke advance the ignition.
 
I know this is old, but have you reverse-engineered any chainsaw ignition modules yet? I am in the process of de-potting an EM unit now.

Perhaps a hard rev limiter that cuts off spark at a particular RPM is not necessary. I have been looking at some advance curves and I was
surprised to find that the ignition advance # goes down somewhat at max RPM.

I am not convinced the ignition timing is actually retarding... instead of the trigger circuit of the timing light reaching it's response time limit and then the visual "display"(flash) is retarded which is visually interpreted as a delay of timing.
Possibly the magnetic field rise and fall time in the core/coil armature is slowing down(reached it's limit) or even more likely the actual electronics in the EI has reached a response speed limit.
I have not really dived into to this much though I have a fair amount of test equipment and a few very good Tektronics scopes and probes including high voltage probes that far out pace these toys we play with.
EM unit?
I depotted a dead homelite EI from a 330. I could make out a few of the key components... power storage cap for the CDI and some supporting diode, transistor and a few other bits. Tough to detect how many different coils were co-wound. I figure there might be 2 or 3.
 
I am not convinced the ignition timing is actually retarding... instead of the trigger circuit of the timing light reaching it's response time limit and then the visual "display"(flash) is retarded which is visually interpreted as a delay of timing.
Possibly the magnetic field rise and fall time in the core/coil armature is slowing down(reached it's limit) or even more likely the actual electronics in the EI has reached a response speed limit.
I have not really dived into to this much though I have a fair amount of test equipment and a few very good Tektronics scopes and probes including high voltage probes that far out pace these toys we play with.
EM unit?
I depotted a dead homelite EI from a 330. I could make out a few of the key components... power storage cap for the CDI and some supporting diode, transistor and a few other bits. Tough to detect how many different coils were co-wound. I figure there might be 2 or 3.

I hear ya regarding the trigger circuit inside the ignition module (igniter): it could be that higher RPM (> 10K) could change the
advance curve in the retard direction due to say, charge time on a cap, for example.

I do not really doubt the reading I get from my timing light, however, since I have seen 2 out of the 4 ignitions maintain full
advance at full RPM. I was just thinking of getting a new timing light with inductive pickup, when I realized that I have an old
Allen scope for ignitions. It is from the 50s, with tubes, but it does have inductive PU. It does not get a lot of use, lately.

"EM" = Electrolux Motors, aka Husky, Redmax, Jonsered, Poulan, etc.

I also have 2 modules (coils with igniters) from unknown makers: one has a logo with "JRG" in it and the other has some
funky graphics, without letters. Both are Chinese, but are not left unmarked. I should take a magnified photo.
 
I know this is old, but have you reverse-engineered any chainsaw ignition modules yet? I am in the process of de-potting an EM unit now.

Perhaps a hard rev limiter that cuts off spark at a particular RPM is not necessary. I have been looking at some advance curves and I was
surprised to find that the ignition advance # goes down somewhat at max RPM.

The following old thread is relavent:
Hi Guys
I had a 330 given to me. PO said it had a bad EI. I put a new rubber carb manifold, chain and got it running and thought there is nothing wrong with this saw??? Wrong....after 3-4 minutes of hard cutting the saw died like you pullled the plug.
I put a NOS ebay phelon EI. $40
Success....:chainsaw:
I cut about 2 pickup loads of red oak.... flawless except for dulling the chain in some dirt. My buddy using a husky 55 was duly impressed with the 330 also

Since I've worked in electronics and electromagnetic s for 40+ years I was curious to see what's making that module tick... Taken a few annotated pix. limitations of my cheap camera are obvious but my eyes can easily see whats going on here...fix would be very difficult but swapping other EI on to another core lamination may be not to difficult.


330EI002ano.jpg

1. There is a typical high voltage coil with insulation paper layers between the coil layers.
2. A coarser coil below that, in the blue coil form, is I believe a charge coil that produces the power to be trapped by a diode into the large charge capacitor (400v dc?).
3. Then at the mid point of flywheel (magnet) passing the coil... the zero crossing of the voltage pulse (single sine wave the transistor is triggered to dump the power from the cap through the coil primary....SPARK generated.
4. Simple CDI ignition

Bad (thermally sensitive until it finally dies) transistor or charge diode and the process goes down the toilet.
330EI001ano.jpg

I did another test as follows:
1. I took a runable EI saw and took the plug out.
2. Drill and socket on to flywheel nut.
3. Spun engine in forward direction to observe the sparks being made.
4. Spun saw in counter direction and NO sparks were observed.

My conclusion is that the magnet polarity sequence DOES matter.
The magnetic field creates a voltage electrical sine wave, that is rectified by the diode into the silver cap, needs to be first in polarity sequence. This bulk power is then trigger/dumped to excite the fine wire secondary. Then you have spark.
If the sequence is wrong...no spark ...

If you expand the previous thread and expand the pix you can see the components I referenced .
 
The following old thread is relavent:


I did another test as follows:
1. I took a runable EI saw and took the plug out.
2. Drill and socket on to flywheel nut.
3. Spun engine in forward direction to observe the sparks being made.
4. Spun saw in counter direction and NO sparks were observed.

My conclusion is that the magnet polarity sequence DOES matter.
The magnetic field creates a voltage electrical sine wave, that is rectified by the diode into the silver cap, needs to be first in polarity sequence. This bulk power is then trigger/dumped to excite the fine wire secondary. Then you have spark.
If the sequence is wrong...no spark ...

If you expand the previous thread and expand the pix you can see the components I referenced .

Thx for the info and pix, Dave.

I would guess the transistor in you photo is an SCR (thyristor). Is there a part # on it? I will search for that
old thread you mentioned. What is the title?

Some of those ignition modules are simpler than others, for sure. Externally, just the 2-pole versus 3, for example.
My Tanaka is only 2-pole, but one pole is over an inch long, where the flywheel goes by it. It has advance.

Looking at another dead module here, I see it has the Husky "H" logo, plus "VIBEMA", and "Made in Brazil".

I have a new inductive timing light on order. Specs show that they are not rated to measure over 10K RPM,
however.

The Husky factory rep at yesterday's World AG Expo openly admits that their cheaper saws have fixed
advance and the pro saws have an advance curve.
 
in the homelite sticky page 434 post 8670

Look in my photo gallery, the poulan section and you can the pix of the skeleton flywheel with 1 piece of load magnet material mounted and cast in between the laminated pole pieces.
The magnetic polarity direction matters depending on the build of the EI

Yes the BIG pro saws would benefit from an advance. Starting in 6-8 deg BTDC for easy starting without a compression release and then advance up for full bore RPM cutting,
 
in the homelite sticky page 434 post 8670

Look in my photo gallery, the poulan section and you can the pix of the skeleton flywheel with 1 piece of load magnet material mounted and cast in between the laminated pole pieces.
The magnetic polarity direction matters depending on the build of the EI

Found it, thanks. So that module you dissected is from a Homelite 330, perhaps from the 80s?
 
Yes I have 3-330's 87, 88, 89. The 88 is the one that had failed.
My cautioning advise is to be sure to use resistor plugs with any EI engine.

Don't a lot of those earlier CD ignitions call for non-resistor plugs? I have also run into this with
80s generation ATVs, but they usually have resistor spark plug caps as well (which often fail).
 
in the homelite sticky page 434 post 8670

Look in my photo gallery, the poulan section and you can the pix of the skeleton flywheel with 1 piece of load magnet material mounted and cast in between the laminated pole pieces.
The magnetic polarity direction matters depending on the build of the EI

Yes the BIG pro saws would benefit from an advance. Starting in 6-8 deg BTDC for easy starting without a compression release and then advance up for full bore RPM cutting,

I think all these small engines (2 and 4 stroke) would benefit from an advance curve, perhaps starting under
10-deg BTDC, and reaching 28-deg BTDC at full RPM. The maker can probably save a dollar or two (Krona or 2?)
by using a cheaper ignition in the Rancher (homeowner) saws.

Also, look at the aftermarket ignition modules for pro saws. They usually do not have circuitry to cut off spark
at a certain high RPM, if that is how they work. Cheaper.
 
Has anyone checked the advance curve of one the units with the long tailed laminations
and then cut off the tail and checked the curve again?
I have a gut feeling the advance curve will change.
And low/idle speed spark & timing (maybe?) gets a bit erratic.
 
Has anyone checked the advance curve of one the units with the long tailed laminations
and then cut off the tail and checked the curve again?
I have a gut feeling the advance curve will change.
And low/idle speed spark & timing (maybe?) gets a bit erratic.

There seems to be a dearth of data on advance curves at all, at least in my searches. Just a quick peak
at a Stihl service manual shows the spark advance spec at 8000 RPM only, and it is specced in mms
and inches BTDC. This saw may have fixed advance....I can not tell unless I test it with a timing
light at different speeds.

As for modifying an ignition module by cutting one of the poles on a long-pole unit, I have never
seen data on that either.
 
That long pole is your advancing.
How faster the flywheels spins, how faster there is a buildup in voltage. How faster you have this voltage, how earlier the trigger activate your secundary coil.
 
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