These coils (one per cylinder) sit at the top of the engine and are covered, so they regularly see temps of 220 deg F. they're fed continuous 12VDC & gnd, and there is a signal from the ECM (control module) that apparently causes the circuit in the COP unit to open and the collapsing magnetic field to generate the spark voltage conventionally . There is also a confirmation signal back to the ECM, for monitoring for successful spark.

I've little experience with these, and haven't dug into their potting yet. From the Toyota forums, they seem problematic.
My question: Which is less reliable, the inductors that actually generate the spark, or the semiconductors that do the switching? If it's the latter I'd like to try replacing the components inside the potting. If it's the former, I'll just chuck the old unit in the trash. Thanks for any informed guesses!

 

I would have to ask "Problematic" how ???
How many articles from known reliable sources have stated that this is a common Toyota problem ???
( Toyota builds some pretty reliable stuff )

Are You building a Hot-Rod ?,
or are You working on the repair of a completely stock Customers daily-driver-Car ?

How many miles and years are on the Engine ?

Were the Spark-Plugs replaced at the Toyota-recommended intervals ?,

Are aftermarket-Spark-Plugs being used ?, or exclusively Toyota-specified Spark-Plugs ?

Were the original Spark-Plugs left operating in the Car until
the Spark-Plug-Gap was worn and had increased to more than ~0.080" ?

What is the "Failure-Mode", ( the "symptoms" ),
that indicate that a Coil has failed, or is failing "intermittently" ?

Does replacing all of the Coils with new Toyota-Parts
always solve all Ignition problems, completely, and every time ?

Trying to replace the internal Electronics is probably a bad idea in any case.

Assuming that the design, or materials, of the Coils is inherently faulty
requires a ton of evidence and proof.

There are plenty of idiots who think that they know something about Cars,
( or particular makes of Cars ),
but they are quite often just self-glorified "Parts-Changers" who have an inflated-Ego.

Someone who races for Money, or other rewards, is a much more reliable source of information.
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Thanks for your reply!
In my case it is a 2007 Camry 4 cyl, MIL code "P0301 cylinder 1 misfire", poor idle, reduced power. 175,000mi on the car.
I haven't used the car since I got the prob, the car usually specifies the cylinder, others say the fix is usually spark plugs worn out, or new coil needed.
I replaced plugs, old ones had normal coloring (including #1) and had the specified gap. No improvement. Haven't received a proper replacement coil yet.

I'm not terribly worried about the car, until the coil arrives and fails to fix it, maybe next week.

I'm more interested in the circuitry inside the old Coil. If it's the subassembly likely to be defective, I'd be inclined to dissolve the potting at the top and explore the triggering components inside, if that's a likely culprit. Otherwise, the literal "coil" part is certainly irreparable by any means, uninteresting to me technically, and I'll just chuck the part. I'm not as interested in a practical repair, as much as testing the "no user-serviceable parts inside" claim.
Thanks for your time.

 

I'd stick with the "no user-serviceable parts inside" theme,
and hope that Rock-Auto isn't selling some "Chinese-Clone" garbage.
( Zero-Warrantee on Electrical-Parts )

And, sorry, but the chances of You being able to "fix-it" are less than slim to none.
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Unfortunately a misfire code does not always mean the coil or the plug. A bad injector can cause a misfire, low compression, worn valve seats, faulty wiring, and the list goes on. Plugs and coils are the most common causes.

As far as replacement parts go get one from a dealer or at least a Denso part. When it comes to electrical parts OEM can save you mountains of trouble.

 

Putting the coils in the hottest possible area seems like a poor choice indeed. Also, while the toy car may be fairly reliable, it certainly appears that they are doing all they can to keep the aftermarket folks out of their market. Different parts every year is one way to do that. And it means that when a part fails while you are in an inconvenient area, you are totally out of luck.

 

I have found in Fords using COP systems its not the electronics or the coil that is the problem. But its spark arc through the insulated sleeve to ground, as there is not a lot of clearance down at the spark plug & its dam hot down there. Usualy i find a small black burn spot on the insulating sleeve around the top of the spark plug. With Ford you have to buy the whole COP assy, when you could easily just replace the rubber boot, but its not avalable.

 

Also, while the toy car may be fairly reliable, it certainly appears that they are doing all they can to keep the aftermarket folks out of their market. Different parts every year is one way to do that.

Do you have any proof of this or is it just one of your "hot air" expulsions?!?

I have never had a problem getting any part for my car from a parts store and some parts are surprisingly low cost. There are certain parts I won't trust from anyone but OEM, but that is the same across all manufacturers.

Edit.

I also have 298,000 miles on the original coil on plugs so they can last and most often do.

 

I observed this when working with a client on the development of fixturing for a filter leak testing machine quite a few years back. The complaint was that every model year the connections were different, and so required different fixtures to seal for the leak test. The claim was that the changes were to make it more expensive for the aftermarket producers so that they would not enter the market. Other companies tended to use the same connection designs for many years.
I admit that this was quite a few years back, and so it may no longer be the case. But at the time it was obvious.

 

Unfortunately a misfire code does not always mean the coil or the plug. A bad injector can cause a misfire, low compression, worn valve seats, faulty wiring, and the list goes on. Plugs and coils are the most common causes.

As far as replacement parts go get one from a dealer or at least a Denso part. When it comes to electrical parts OEM can save you mountains of trouble.

As I was reading the problem and comments I was quick to ask "How do you know it's a bad spark coil?" I also thought of a friend who had a car with an engine light. The problem was "Misfire at idle". The cause was poor compression. This same friend had a van that had been running rough. One day it wouldn't start at all. So he started replacing all the spark plugs. No luck. Replaced the distributor, rotor and points (remember those?). Again no luck. He was in the process of putting all new spark plug wires when I walked up and asked "How's it going?" He said the van had been running rough and hard to start. Today it wouldn't start at all. I asked him to crank the engine and let me give a listen. There it was! The familiar sound of NO compression. The timing belt had broken. When I told him that he asked how I knew. I told him I could tell by the sound. He didn't believe me until we removed the timing belt cover.

The moral of the story is this: "Fully diagnose the problem before throwing parts at it." I ask again; are you certain it's the coil? One quick way to tell is to swap it with another coil from a different cylinder. If the problem moves with the coil then yes, it's a failed coil. But if the problem persists on the same cylinder no matter which coil is in that position then chances are good it's not the coil. How to tell? Run the engine to running temperature. Squirt a little water on the exhaust manifold on each cylinder. The one that doesn't sizzle is the one misfiring. If the problem remains in the same position then it's time for a compression test. It could be a burnt valve, bad cam lobe or even cracked rings.

How many miles on your Camry? Oh, wait; you said:

In my case it is a 2007 Camry 4 cyl, MIL code "P0301 cylinder 1 misfire", poor idle, reduced power. 175,000mi on the car.

I'd suspect mechanical issues rather than the coil. Oh, it's possible you have a bad coil, but I'd think it's more likely rings. If the car has been run without an air filter - yes, rings and cylinder wall are scored. My neighbor? He put a K&N air filter on it but never oiled the filter. Dust was getting through and wearing the cylinder walls and rings.

 

These coils (one per cylinder) sit at the top of the engine and are covered, so they regularly see temps of 220 deg F. they're fed continuous 12VDC & gnd, and there is a signal from the ECM (control module) that apparently causes the circuit in the COP unit to open and the collapsing magnetic field to generate the spark voltage conventionally . There is also a confirmation signal back to the ECM, for monitoring for successful spark.

Where did you get this info? If fed 12V continuously then there's no magnetic collapse. Unless there's a third wire, one that triggers (or shuts down) the transistor. There's more to this than your description covers.

 

Looks like we never got a final answer on this. Been a while since I was here.

 

On most ignition spark coils the feed (supply terminal) is constant and it is the other side of the circuit that is interrupted. In the old "breaker points" systems that was a direct ground to the points being opened, the 12 volts was always powered when the engine was enabled.
( this is in response to post #12.)
My point being that ALWAYS, except for a CD ignition system, THE 12 VOLT FEED TO THE COIL IS ALWAYS CONSTANT!!! The coil current is switched on the "ground side!! So the spark is delivered when the ground side connection opens.

 

With COP set ups if theres 2 conections the switching is done in the engine ECU. If theres 3 conections then the swiching is done in side the COP.