Lexus GX 460 2012 130k miles, spark plugs were done at 117k in early 2022 by our own 1Ags.

Back in August I had a hard braking incident where I turned off the vehicle shortly thereafter (if 4Lo/Check engine came on I didn't notice), and next time I started her up they were on and it was a p0351 code.

Drove fine, no misfires, code cleared.

Came back in early October after a not as hard braking incident. Code cleared and drove fine.

On another forum a guy claimed he had this for years on a Tundra and tracked it down to an electrical issue from the ABS sensor which he replaced.
That didn't sound right to me....

Decided I would be a good owner and just switch out the coil pack for #1. I assumed #1 was front driver, but on another forum a guy swore it was passenger side.
So I put the new coil into front passenger and all was still fine.
But I did some more research and realized #1 was certainly the driver side.

This morning I put the old coil from #2 into #1 and immediately got p0351 and the engine was obviously misfiring.
Put the old coil #1 back into #1. Same
Bought a new Denso coil. Same

There was no oil or anything in either #1 or #2

Now I'm at a loss. Seems highly unlikely it is the spark plug which is not old. But it's easy enough to give that a try tonight.
The wiring harness on #1 seems fine. All 4 wires. Clicks snug.

I have googled and searched at clublexus and this error never comes up.
Any ideas?

Why did you switch out the coil pack if it was driving fine?


Also:

https://www.clublexus.com/forums/rx-2nd-gen-2004-2009/958655-p0351-ignition-coil-pack-cylinder-1-nightmare-solved.html

Quote:

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End of story- sometimes if a coil pack fails in a special way a P0351 is really a P0351, P0352, P0353, P0343, P0355, P0356 but the ECM leaves the extra codes off. This could lead to replacing a coil pack on the wrong cylinder and possibly an ECM by mistake when it was neither.

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Also, pretty sure 1, 3, 5, 7 are on the drivers side. 2, 4, 6, 8 are on the passenger side

I got the error twice so figure putting in a coil pack before it left me stranded would be prudent

I'm not feeling confident that a new plug will solve the issue. And that post has me concerned I'm just chasing.

But it drove fine.
I replaced coil 1 with an old coil and immediately something is now misfiring.
But I put in a new coil and still something is misfiring.

Seems very suspect that it could be a different cylinder with an issue, right?

That does give me some debug tips though. I do think in the end this has to be a coil pack issue.

on #1 wiring harness (disconnected from coil) I have 12V power, but never see 5V power on IGF.
I've tried this with all other coil harnesses connected, and I tried with #3 disconnected.

on #3 wiring harness (disconnected from coil) I have 12V power, the 5V on IGF, and the pulse on IGT.

Since IGF is shared, it seems I should see this on each harness. But I never see it on #1 harness, even when I pull #3 harness from the coil.

If this was an issue of #3 coil shorting then when I pull the harness I would expect to get 5V on IGF at any harness but I don't.

So this seems like a wiring or more likely ECM issue right?

Just. Slap. In. A. New. Plug.

What are they... $8? It's not unheard of to have a bad plug out of the box.

It's clear you have your head wrapped nicely around the technical aspects. So... don't overthink it. New plug.

While I agree throwing a plug is cheap - and easy if one of the front plugs - I really don't see that being the issue with what I've described.

Well, I think the missing signals issue was maybe not getting a good connection with my meter tips. I can see the appropriate signals on the connectors today.

Put in a new plug and has the new Denso Autozone coil in #1. No change.

I can tell a cylinder isn't working due to sound / shaking. Pulling the connector on #1 and #3 (easy to reach) make it worse so I don't think it's either of them.

The coil in #2 is a Denso from Amazon….thinking about throwing a new plug and a coil from autozone in there as a last resort?

Otherwise towing to clear choice and let them debug.

Sigh.

Sazerac said:

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Well, I think the missing signals issue was maybe not getting a good connection with my meter tips. I can see the appropriate signals on the connectors today.

Put in a new plug and has the new Denso Autozone coil in #1. No change.

I can tell a cylinder isn't working due to sound / shaking. Pulling the connector on #1 and #3 (easy to reach) make it worse so I don't think it's either of them.

The coil in #2 is a Denso from Amazon….thinking about throwing a new plug and a coil from autozone in there as a last resort?

Otherwise towing to clear choice and let them debug.

Sigh.

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Swap #1 and 2 coils

That's what got me into this mess.

But the problem is that the code always reads for #1 and I'm pretty sure it's not #1 failing. So that wouldn't help.

Have you visited an enthusiast site? Likely your problem isn't new... and you may find a solution in a forum associated with your vehicle. Sounds maddening... and you've done eeverything I'd do. Good luck.

I had misfire problems once on a vehicle and the spark and coils were fine, but the rubber insulation on the coils was dry and had tiny cracking at the tips due to age.

I replaced only the rubber insulation on all coils for $40 ($5 each on a v8). This fixed all of my issues.

I didn't need to replace the coil.
At 100k miles, check the coil insulation rubber, if you see any signs of dry rot or cracking at the tip, then replace it. You might be able to get the rubber only is redd of having to get a whole new coil depending on the design. My vehicle was a 2002 mustang GT.

Under what conditions is it misfiring?

If it's misfires under a specific engine load, like heavy acceleration, it could be related to the resistance in the spark plug circuit at the time it tries to fire the spark, which goes up with cylinder pressure,

It's pretty clear at least one cylinder is completely dead at startup. I sent it to a Lexus repair place. They claim their computer will read out the data and tell them which one so hopefully it's just replacing a coil on one of the other ones.

They ran compression tests and everything is good.

They have never seen these errors on this engine. Have a former lexus regional specialist taking a look.

I figure it's gotta be electrical / computer with the way this all went down.

They found it! One of the wires in the harness to #1 was a little loose and just not quite making the connection.

Sazerac said:

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They found it! One of the wires in the harness to #1 was a little loose and just not quite making the connection.

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So did they replace the pigtail?

They just repaired the wire kept the harness.

Sazerac said:

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They just repaired the wire kept the harness.

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Excellent!

Sazerac said:

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They found it! One of the wires in the harness to #1 was a little loose and just not quite making the connection.

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Nice.