2001 3.4l 232k CEL P0304

I got a pretty cheap 2001 Tacoma with the 3.4l V6 with 232k on it about a month ago. When I got it, it had a rough idle, and three codes on it P0441, P0450, and P1135. I replaced the front bank O2 sensor, and the Fuel Tank Pressure sensor and cleared the codes and all was good. Except the rough idle returned shortly after. Then a weird power band issue where between 1000RPM-2000RPM if I floored it, the engine would stutter and give a few times like it was missing a cylinder. Misfire was in the back of my mind, but I stayed hopeful. Seafoam and a plan for a new timing belt and water pump with new plugs and coils and wires was set in motion to ease my worries. Then yesterday on the way home from work I noticed the skip felt a bit worse and the stuttering felt more pronounced; followed by the CEL. Throwing a code P0304, fears became reality and now a bad seated valve or head gasket is plaguing my mind.
I'm doing a compression test when I get home today as well as a borescope check. I'll post my findings tomorrow with pics.
Posting this in case anyone has had similar issues or has seen any threads with similar issues. I've read most of the main one's while winding down last night but doesn't hurt to ask.

 

Last night I did the compression test, I follow timmythetoolmans (i think that's his name) guide but pulled the EFI fuse. Plug wire tabs snapped on me and I needed plug sockets to get the plugs out of their little despair pits and was able to pull them no problem after a q harbor freight trip. Sockets were pulled and here are pics of them; their cylinder is labeled in the background on the cardboard.
#1

#2

#3

#4

#5

#6


Single electrode! Toyota even put a nice little sticker to remind people the engine takes double electrode plugs. But looking at the tips their all consistent which is good to see, HOWEVER there was some "burn marks?" on cylinder #4's plug:




Not sure what causes that but probably is related somehow... I also took pictures of all the wires and coils and whatnot, with their corresponding cylinder labeled on the cardboard in the background, will be attached here:









Finally got to the compression test, was super nervous doing cylinder 4.... BUT we have compression!!

Infact cylinder #5 was my weakest but even then 20 PSI over the worry number. #4 seemed right in line with all the others and they all held that second number for 3 minutes or so with no change!
So grateful to have compression, means this miss fire is probably the plugs, plug wires, coilpacks, fuel filter, or injectors. So I'm going to go ahead and replace all of them
Speaking of which I believe FRgeoff made a thread bringing up that the denso equivalent for the injectors are denso lexus rx300 = 23250-20020 or 23250-0A010. I found them on Injector Rehab here:
Lexus Toyota RX300 Avalon Highlander Camry Injector 23250-20020 (S6)
and here
Lexus Toyota RX300 Avalon Highlander Camry Injector 23250-0A010 (S6)
I'm fine with getting them as long as these are the ones I can just plug and play. Again FRgeoff made his post here:
Injector PSA: V6 3.4L 5vz-fe 1st gens | Tacoma World
and his claims are that these are just plug and play. But on Motorwest Performance they have specific injectors for the denso upgrade for the 5vz:
Enhance Performance and Reliability with 5VZ-FE Fuel Injectors | MotorWest Performance
and their housings are very different looking. I plan on getting the injector rehab ones, but I just want to double check or atleast give someone the chance to put me on the right path with this. Any recommendations would be appreciated!

 

Carbon arcing. Replace the wire... you used to be able to get indiviual wires, not so sure anymore.

 

That's carbon tracking, almost certainly is causing your misfire. The spark will follow the carbon track under high load conditions instead of arcing across the plug electrodes like it's supposed to.
A set of plugs, wires, and coil boots and you should be good to go, I wouldn't do anything with the injectors.

 

I'm having a similar issue with my 2003 (340K on the clock)... mine idles fine (mostly), but wants to misfire under acceleration from stop or at speed... I'd replaced the plugs about 3-4 months ago, and it seemed to go away for a bit then came back... read that the plug wires could be an issue so I pulled them off and found that the #4 tip connector had broken off and was apparently just arcing in the boot. Thought that plug wire replacement would fix it, but after driving it the misfire is still there. With this many miles on the clock I'm wondering if I have another sensor that's giving me an issue?

Some of the other options are...
MAF sensor
MAP sensor
Fuel pressure regulator

Is there a computer that can plug into the system and watch what the ECM is seeing in real time? I have my $20 OBDII reader so I can read/clear codes, but an actual live monitor would tell me if there was a sensor that was reading out of parameters and causing the ECM to lose it's mind. Thanks!

 

There are many scan tools on the market. My goto is tool is BlueDriver and if I need more functionality I will use one of my pro level tools.

 

Well as a follow up, I got my Taco sorted out... with the mileage, and the fact that I'd replaced one coil with a cheap unit a while back, I just replaced all of the coils with new coils (Amazon, NGK U4016 (48983), ~$60 ea) and that cured my misfire issues completely. Should be good for the foreseeable future. Good luck!