Testing for spark on new Echo chainsaw

[R_C]

Last fall I bought a 16" Echo chainsaw from Home Depot for something lighter and safer than my 50-year old McCulloch, which never had a chain brake. I used the Echo a few days last fall and once last week. But last week I could not get it started again about an hour after I used it. It wouldn't even attempt to start so I checked for spark. I removed the plug and grounded it while cranking. No visible spark. Pulled the kill switch wire from the coil. Still no spark. Switched to a known good spark plug and still no visible spark even when spinning the engine with a drill. Tried an inline spark test light and no visible light there either. Tested both the spark plug and the inline test light on my McCulloch and there was good spark and blinking light by just spinning the flywheel by hand.

The Echo's plug gap and the coil to flywheel air gap are both good. The ignition coil's secondary winding measured around 2.7k ohms, which appears good. I understand you can't test the primary winding on these newer coils (it reads about 120k ohms) so I ordered an OEM replacement coil. Same result. No visible spark at the plug or test light. I used Echo's online support to get the coil test specs (2.5 - 2.9k ohms) and they recommended I bring it to their nearest servicing dealer.

Today, before I headed to the dealer, I spun it again and still no visible spark. I put the plug back in and installed the cover and it fired right up. What? The saw still has problems starting when its warm so I brought it to the dealer for testing anyway. Is there something about these newer engines that prevent seeing a visible spark at the plug while grounding it to the block? Lower voltage? No spark unless there is compression? How do you test for spark?

 

[Steve_P]

I've had a tester like this for small engines for many decades. It has a much larger gap to jump than a plug, and a clip for easy use with one person. If it doesn't like to start when it's warm, that's typically a coil failure. But I don't understand why you're not seeing spark when it's cold.

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[Beerhippie]

How bright was the environment when looking for a spark? It doesn't take much to wash it out.

Next time, just stick the plug on your tongue and give the cord a pull. Much more reliable.

 

[Steve_P]

How bright was the environment when looking for a spark? It doesn't take much to wash it out.

Next time, just stick the plug on your tongue and give the cord a pull. Much more reliable.

True, spark on a plug can be hard to see outside on a sunny day. With the tester I linked above, you can hear it crackle when it jumps. If you're not deaf, it's relatively quiet....

 

[Mandres]

Sure the ignition switch was on?

 

[seber]

I check for spark with an old school inductive timing light. Easy to see even in bright sunlight and no interference in the circuit.

 

[R_C]

I was indoors when looking for spark and working at the same bench where I had my McCulloch disassembled. I moved the Echo's spark plug to the McCulloch and got a very bright visible spark with a manual spin of the flywheel. I also put my spark tester (similar to the one below) on the McCulloch and again it was very easy to see the tester's light flicker. The kill switch is a spring loaded normally-open momentary switch and I tested it to make sure there was no path to ground unless the switch was activated. I also did most of my spark testing with the kill switch lead disconnected from the coil.



I am stumped. I never once saw the Echo's plug spark or the test light shine and yet it still started. I thought it might be due to some new technology but all of your replies so far suggest I haven't overlooked something obvious.

 

[R_C]

I check for spark with an old school inductive timing light. Easy to see even in bright sunlight and no interference in the circuit.

That's a great suggestion I had never considered for small engines. Just hooked up my old Craftsman inductive timing light to the McCulloch and it works like a charm. Nice bright light. I will remember this tip.

 

[Beerhippie]

That's a great suggestion I had never considered for small engines. Just hooked up my old Craftsman inductive timing light to the McCulloch and it works like a charm. Nice bright light. I will remember this tip.

Unlike a gap-type spark tester, the inductive light doesn't tell you anything about the quality of the spark. You may have a weak coil, but it'll still trigger the timing light.

 

[R_C]

Unlike a gap-type spark tester, the inductive light doesn't tell you anything about the quality of the spark. You may have a weak coil, but it'll still trigger the timing light.

OK. Good to know.

But why does a 50-year old all original ignition (points, condenser, coil) on the McCulloch give such a nice visible spark at the plug and no visible spark on the Echo. Weak coil? The Echo dealer said it may be several weeks before they get back to me. They said they will run many tests and go back and forth with Echo before they let me know their results.

Because of these issues with the Echo, I am now doing a nice restoration of my McCulloch Pro 10-10 Automatic. I rebuilt the carb, bought another off eBay for its chain brake, and just primed all the parts for paint tomorrow.

 

[seber]

Unlike a gap-type spark tester, the inductive light doesn't tell you anything about the quality of the spark. You may have a weak coil, but it'll still trigger the timing light.

You don't need to know the quality of the spark. If the light is flashing, then the plug is firing.

 

[R_C]

I'm still stumped but here's an update. The Echo dealer called and said they ran tests with the saw cold and warm and everything checked out. They noticed it wanted to die while idling so they increased the idle rpm, which wasn't covered under warranty so that cost me $56. I just picked up the saw.

When I got home, I immediately removed the spark plug and checked for spark. Nothing. I tested for spark with the inductive timing light and again nothing, which seems to confirm why I've never seen a spark. I put the plug back in and it fired right up. With the saw running the timing light flashes nicely. I've checked for spark using both the recoil starter and spinning with a drill. I've tested with and without the kill switch lead connected to the coil. I ground the plug's hex head to the top of the cylinder head when testing for spark. How can the plug only spark when it is installed in the cylinder? What am I missing?

I still think there may be a problem with the coil when it is hot. But right now I don't have a way to test for spark when the problem occurs again. Here's a picture of the coil and plug for reference.

 

[Beerhippie]

I'm starting to think that there's some electronic magic inside that mag coil.

 

[Wamsutta]

I check for spark with an old school inductive timing light. Easy to see even in bright sunlight and no interference in the circuit.

How are you powering up the timing light? The light I have has an inductive pickup and two cables to hook to a 12V battery.

 

[Steve_P]

You don't need to know the quality of the spark. If the light is flashing, then the plug is firing.

Compression changes things. This is why spark testers have such a large gap to jump. Obviously, you will now argue because you know more than the people that make spark testers- which evidently have no purpose, but for some reason factory service manuals call for them.

 

[RTM]

I wonder if the threaded (insert?) in the head has a different ground quality than the exterior of the head. Only thing that jumps into my mind.

Is there more than 1-2 ohms difference across them?

 

[R_C]

I'm starting to think that there's some electronic magic inside that mag coil.

Me too. But what could the coil's electronics be sensing? Can't imagine it's compression. And I doubt rpms would have any purpose. I'll do some searching and see if a service manual is available.

 

[R_C]

I wonder if the threaded (insert?) in the head has a different ground quality than the exterior of the head. Only thing that jumps into my mind.

Is there more than 1-2 ohms difference across them?

I thought of that earlier and tested for continuity. But I just tested resistance and got zero ohms between the cylinder threads and top of head.

 

[R_C]

How are you powering up the timing light? The light I have has an inductive pickup and two cables to hook to a 12V battery.

My light is the same. Inductive pickup with a direction arrow to point to the spark plug and positive and negative leads for 12V power. I connected the light to an old 12V battery I keep in the shop for just such purposes. Again, no light when testing with the plug out and grounded to the top of the cylinder head. But plenty of light with the engine running. I tested this timing light setup with the disassembled McCulloch on the bench and the light flashes just spinning the flywheel by hand.

 

[seber]

How are you powering up the timing light? The light I have has an inductive pickup and two cables to hook to a 12V battery.

I always seem to have an automotive battery around.

 

[seber]

Compression changes things. This is why spark testers have such a large gap to jump. Obviously, you will now argue because you know more than the people that make spark testers- which evidently have no purpose, but for some reason factory service manuals call for them.

If you use a timing light correctly, it will be under compression.

 

[R_C]

I'm starting to think that there's some electronic magic inside that mag coil.

I searched some more and found an Echo spark tester with part#s 897800-79931 and PET-4000. PET-4000 appears to be a widely used spark tester that allows you to change the plug gap to test the coil. A youtube video I watched shows testing with both the simple inline spark tester I have (example picture above) and the PET-4000 with the spark plug installed. So I tried my light again with the plug installed and it lights. So the coil does require an installed spark plug to spark. I have always visually inspected a plug's spark. But with these new ignition coils you can't test for spark the old fashioned way. You must use a spark tester with the spark plug installed. Lesson learned.