97 3rz p0304 code when warm starting

97 regular cab 3rz 5 speed 4x4. engine was fully rebuilt. new pistons, balancing shaft delete, new head, new cams, new injectors, front cover. The truck runs amazing !!!
short trips will misfire on startup CEL p0304 running on three cylinders. walk away let it cool right off, come back and starts no problem and once again runs excellent. Tried new 02 sensors (both denso) new coil packs plug wires and plugs all denso parts. no difference same scenario (when warm 304 code, misfire number 4) let it cool right off fires up no problem. swapped injectors around (I'm trying anything) same thing runs great, kill it when its warm and will fire back up on 3 cylinders with 304 code misfire number 4.. i can take it for long trips as well without problems, just doesn't like firing backup when warm, instant 304 code.
Crank shaft and camshaft sensors are original and might me the problem... but getting tired of buying random sensors, any help with words of wisdom would be greatly appreciated

 

Make sure all your grounds are solid and good

I would live scan and see if its running lean or rich.........idle and hwy


worst....I'd be suspicious of a coolant leak....
what are conditions of the head....new/old/rebuilt

the oem heads are very prone to cracks between valves.....
and not so easy to detect..
another tacoma Achillies heel


bad crank shaft sensor would just result in random no starts.

 

brand new head and cams. valve lash was set to oem specs by the machine shop. i don't have a live scan tool just a code reader so i guess that's next on my shopping list

 

Typically a start up misfire is a leak, coolant, fuel, oil, something is leaking into the cylinder.

After cold soak you'll need to put a camera into the cylinder and see.

 

No coolant or oil loss. No black or white smoke. I do have a camera I will pull the plugs and do some investigation

 

We've found with Toyotas its just a tiny amount of coolant that can cause this, you wont see smoke or need to add coolant. It mists in.

 

brand new toyota head, freshly decked block assembled with toyota gaskets engine has less then 3000 miles, i guess it is possible just extremely rare for toyota parts to fail that quickly. I was really hoping for an electrical issue. off to the garage i go...

 

Many times the parts don’t fail…..
The person that installed/assembled said parts made a mistake(like myself…ugh)

good job swapping injectors

bc the issue occurs consistently when warm is a clue

head/block expanding bc of op temperature
And somehow popping obd code

maybe head bolt(s) need re-torque?
Maybe upon installation, HG pinched/compromised/moved to incorrect spot?

compression/leak down test could confirm this guess

 

Mini camera and the compression tester are coming with me to the shop. Hopefully it’s not head gasket issues. Thanks again to everyone. Keep your gen1 on the road !!

 

You know these have those pesky injector cups.....
double check and make sure that is well
maybe there is an intake leak back there


these engines are so simple......I doubt its the HG......

stuck egr.........if you had a good scanner it would tell you solenoid positions and other


That temp sensor should of been replaced.....and crank sensor.....at least on a new engine
pigtail gets ate up over time/heat/grease....

 

Good call on cups

OS told me while back, dude chased an issue for months
Cracked I. Cup letting in un-monitored air into combustion chamber….lean condition….pops code

that should be easy test with chlorinated brake clean test when engine at op temperature

 

hey guys back again truck magically fixed itself while I was trying to diagnose the problem . ran like a top for over a month, and all of a sudden one trip to the store and the p0304 code comes back on a warm start up. it has to be an electrical problem. ive been down each spark plug hole with a mini camera no HG breach no cracks the head. like i said truck ran flawlessly for over a month. extremely hard to diagnose. so many new parts barely 4000 miles on the rebuild . extremely odd that the problem went away for over month only to return again.

 

Think you need to smoke it......look for intake leak around injector or its cup....
check #4 compression

these point distributors cause weird problems......I damn sure dont want to be expert there

 

Compression is great across all 4 cylinders. Smoke test I have not tried, that sounds promising. Points distributor ?? There is dual coil packs. No distributor. I daily drive the truck and it runs excellent. No problems for over a month and then a random p0304. You don’t think it could be a broken wire somewhere in the harness ?

 

Just to eliminate everything possible, check valve clearances. It seems like you have eliminated most things external by swapping them around. Being that it is reproducable is 90% of the battle. If this were me I would find the wire/connector on the PCM or the #4 injector and with a test light see if there is power out all the time. After that I think you are getting into scope territory... I bought this https://www.aeswave.com/uscope-basic-kit-p9621.html over a year and as things auto repair go I have not had the need to use it yet and I hope it stays that way if you know what I mean.

 

Just want to say thanks to everyone for all the info. Nobody locally gives info like all you gen 1 enthusiasts. I’m confident with a new list of things to try I will win. Back to the garage I go. Thanks to everyone I’ll keep you posted with my progress