3rd Gen 5vz-fe Hot Misfire

[SlayTank]

Hey guys, new to writing in forums but not to reading forums.

Anyway I'll put some info down to maybe help someone in the future as this forum has been especially helpful to me.

what happen:
Started the runner in the morning drove to work, ran fine.
4 hours later drove to the doctors, ran fine
Started the runner half hour later, temp outside was about 105, engine was warm and sat in parking lot. On start up instantly felt a misfire. No check engine light at this time. it was missing all the way back to work.
4 hours later drove to gym. No misfire but check engine light does come on.
1.5hours later leave gym. instant misfire and check engine light is on.
Misfires to a parts store, they check codes. Says number 4 misfire and something about o2 sensor.
Drove home missing all the way, replace front o2 sensor, start immediately misfire is still there.
next day starts fine. I only move it under some shade to began working on it, no misses.
I check the spark, its good. I check the voltage for the injector at the ECM it reads good.

The speculation: I have read a few threads on here about the injectors going out and working when cold but not after a hot start. I believe this is probably the issue. Fuel pump and fuel filter replaced 3k ago so i do not believe pressure to be a problem.

I am about to drive it and test my theory. It is 111 degrees here today so heat is going to be a issue.

...Bring on the heat

Feel free to weigh in if you got 2cents or questions

 

[98OzarksRunner]

Given that #4 has the plug wire coming from #1 coil I would check that wire (change the plug wires). I'd also check the plug. The O2 sensor would probably read rich (thus the code) if you had a misfire so it's likely the sensor itself is not bad. It's a whole lot easier to change plug wires (and pretty cheap) than change injectors.

 

[SlayTank]

So it did exactly what i thought it would drove it to the store, ran fine
Started it to leave and there is that misfire.

I checked the plug and the spark on number 4 when it was cold and all was good.

the spark is good while its hot too.

I'll probably check the restansie of the wire just to double check. Manual says 25K ohms max. i'll probably check the volts at the ecm for the injector again too.

i'll update again later

 

[SlayTank]

pulled the plug wire to check ohms and the dumb little clip that holds the wire to the coil broke. ohms tested at 15k so thats good. but i pulled the trigger on some new denso ones anyway. I just put the wire back on the coil and drove real short distance to the store and it ran totally fine.

when the new wires get here, i'll toss them on and we'll see what happens.

 

[SlayTank]

ALRIGHT EVERYONE! I got the new injector from rock auto, a GB rebuilt one. I yanked the intake off tested the #4 injector ohms it tested good at 14.1 ohms when cold. I came inside and tossed it in the oven just long enough for it to get hot, pulled it out the oven, tested again... Annnnnd... drum roll... outer limits!... which means there is a open in the injector when its hot. There is a break in the electrical connection only when hot. also of note: the stock injector is plastic and the GB rebuilt one is metal. I thought the stock ones would be metal too... guess not. also the metal one has one extra seal where the plastic ones just are molded with that extra hump. the nozzles look different too. Do any of you know why they are different? when they changed them? just curious.

I just check the bad injector again after it cooled down and now it reads fine again. There it is, thats why a only hot misfire. hope it helps someone.