Help! Coil 3 keeps blowing!

Good evening, I am a new member here but my first truck I've owned for 5 years now is a 2003 Tacoma 4x4 with the 3rz. I've loved the truck and everything is stock on it. But for the last 2 1/2 to 3 years, I've had a big problem with it. The truck keeps eating coil #3. About every 4-6 months it starts misfiring and it's cylinder 3 every time. I've seen forums that say the injectors needed cleaned, that it was lean in that cylinder and causing the coil to overheat, so I had them cleaned and then it just blew again. This is probably my 5th coil or so and I'm losing my patience with this truck. I run NGK coils and ngk plugs, other than that, everything is stock. If someone could offer some advice as to what it is, I'd greatly appreciate it.

 

Could the spark plug be shorting out?

 

Could just be crappy parts but I'd be concerned about possibly excessive coil dwell but the only way one could determine that is with a scope.
Are you sure it isn't just a bad connection and your inadvertently fixing it by changing the coil?

 

I'm not sure what you mean by a spark plug shorting out, I've had 2 sets of plugs in it since this started happening, so I'm not 100% sure what you mean by a plug shorting out.

 

Spitballing mostly. If for some reason there was no load on the coil and it was firing into a short, that could be damaging. But then again you’d probably notice

 

From what I've been told the NGK is a good part no? And if there was a problem with the dwell wouldn't it blow on all the other cylinders too? Cause with mine I don't have plug wires, it's the coil on plug design. I've check everything over multiple times with the connection with the coil and everything is fine on that end. By bad connection do you mean in a different place other than the coil?

 

Ah ok I see, but the coil is bolted onto the cylinder head and when I put the coil on I can feel it click onto the plug then I bolt it onto the valve cover. This is why I'm thinking it's not the coil and maybe a problem in another spot possibly?

 

Their plugs are generally good I can't speak for the coils as I didn't even know they made coils.
Are there any signs of damage, arcing, or melting on the coils when they go bad?
When I say bad connection I mean it could be poor pin fitment in a connector or a broken/shorted wire that gets disturbed by changing the coil.

The coils are each controlled individually by the PCM, they share a common power, ground, and feedback wire so theoretically a driver in the PCM could be going wonky or something else screwy is going on but like I said the only way your gona find that is with a scope.
This is the coil control pattern from a 4.0l they use basically the same system, the top line is the #1coil control, the bottom line is the coil confirmation signal.
The amount of time the coil control wire is held at 5v is the dwell time (3.3ms in this capture).

 

Swap coils with another cylinder to see happens.

 

I've done this the last couple times and it follows the coil, the misfire will carry onto the cylinder that the bad coil is on, however it's the same cylinder (cylinder number 3) that keeps blowing them though. Every time it has been cylinder 3 that does this and not any of the others.

 

Ok that makes sense. And in regards to any physical marks, there are not any. The only thing is when I take the coil off I noticed it smells like burnt plastics and rubbers of sorts. I know that's a very vague and basic answer but that's the best I got haha. I have not traced the wires going back from cylinder number 3 to see if there is anything wrong with the wiring so looks like I'm going to have to test all of what you mentioned. Unfortunately I do not have the tools to do that, do local shops have tools like that or is that a tool you bought?

 

I suggest a compression test, leak down test, valve adjustment, valve cover and spark tube gasket replacement.
3RZs need valve clearance maintenance.

 

Shops should have one as there's many issues that can't properly be diagnosed without one but unfortunately many shops still don't have one or even know how to use one.
I work at a shop and have my own but I'm the only one here that knows how to use it.
I mean it could still be shitty parts, it's hard to say.

 

Update: I made a rookie mistake and assumed it was coil number 3. It wasn't. It was coil 1. Everyone can make fun of me now for assuming instead of reading the codes haha. So now looking back, the first coil to blow was coil 2, then coil 3 multiple times, now coil 1. Anyone have anymore suggestions? Thank you all so far.

 

I put the new coil in and it ran great FYI. If that helps with anything?

 

I think I'd chalk it up to shitty parts

 

Got any recommendations for a good set of coils? Haha

 

I believe Denso is OE, aftermarket parts are a toss up it seems like especially these last few years.
Standard Motor Products used to be good, now much of their stuff is china made junk too.
I don't really know what other brand coils are out there besides parts store branded junk.

 

How old are the plugs? Are they gapped correctly? If there is too big of a gap the coil has to work much harder, it will generate much more heat and die prematurely.

 

Have you checked or replaced the plug wires yet? You can check the resistance of the coil wires and see if they are in spec. If the primary side was shorting out it would blow a fuse, if the correect 7.5 amp fuse is used. if the secondary side (the coil) is shorting out that would blow the coil pack I beleive.