zcarjoe

So what a weekend I had,

Here's what I have. 216000 miles on a 2004 GX470 I picked up a few months back that was neglected. Original plugs and coils and recently started throwing a P0355 code. I knew the plugs were toast so I put in new NGK IR plugs and the code remained and now idled rough. I swapped coil packs 1 and 5 and now had a P0351 code, so ok I need a new coil pack. Installed the new Denso OEM coil pack on cyl 1 and back to P0355. Swapped the new coil pack back to 5 and still misfire on 5. I checked the plug and swapped it thinking it could be bad as well but no matter what I do I still show a miss on 5.

After this game of ignition musical chairs I checked the connector and wires to it and they appear to be great so my frustration continues. I took a borescope to make sure there wasn't any burrs grounding out my plug and it looks great.

So what's left? I am going to cut back the wire loom and expose the wires to that coil and see what's what. Would the injector throw a separate code? Perhaps that's bad or clogged? Perhaps a bad headgasket or bent valve causing low compression?

The confusing part is my initial diagnosis when I swapped coil packs 1 and 5 and had a P0351 code that I cannot replicate.

Any help would be appreciated. I am new to the 2UZ but not new to cars. Just wondering if there are any other bugs that may cause this?

Thanks

IanB2

I'd do a compression test at this point to rule out mechanical issues with cylinder 5.

chiph9

1. Double-check that the connector seated all the way on #5. And that it "clicked" solidly.
2. I would also follow the wire bundle back, feeling for any rough spots, in case an animal chewed on it.
3. Reset the computer by disconnecting the negative battery terminal for 1-2 minutes. When reconnecting, try for minimal sparks (be fast and accurate with the terminal).
4. Swap a different coil pack (not the new one, not the original) and see if the code clears)

Chip H.

zcarjoe

I found it. Bad signal wire back in the loom by the firewall.

chiph9

Bummer. Glad you found it.

Chip H.

IanB2

Was the harness damaged? Sounds like a real PITA to track down, good job!