P0304 on 2020 TRD Tacoma

My buddy’s truck started throwing 0304 a few weeks ago. I know he hasn’t kept up with maintenance so i went ahead and grabbed a set of plugs and helped him swap them out. Also made it a point to swap the #4 coil with #3 while I was in there just to make sure it was or wasn’t coil related.

Plugs were between meh and bad, as expected. From other issues though. They went way over on an oil change and since then they have valve stem seal leaks on 1 and 5. Plug 1 was wet (light coat of oil) and plug 5 was almost completely crusted over.

Truck instantly ran much better but code still came back.

Now when the code “comes back” it’s been associated with a notable engine miss and thats when the dash lights up. Im going off what i’ve been told by two NOT car people. They described it as being able to feel the engine power drop out for a second causing a felt lurch in the truck.

They said that has only happened once since the new plugs installed.

We all live out remote in the desert and constantly have rodent wiring issues so yesterday I met up with them and snaked a bore scope down to the fuel rail to take a look at the wiring, everything looked pristine.

My next step is going to be hook a compression tester up to cylinder 4. If that comes up good part of me just wants to stuff a new OEM injector in #4, even though I think I should know better.

Hoping someone might have some input before my impatience lands me playing part swap roulette like an idiot.

 

My guess is he's still driving it......
You can put a stethoscope on the injector & see if it clicking, that would tell you if theres wire damage....

 

What would make you think that, the 12,000 mile oil change interval maybe? Yeah he’s still driving it. I dont have a stethoscope out here unfortunately. They are stopping by today. I wonder if I could go old school with a metal dowel or something of the sort. Seems like a long shot though. Id imagine and ticking from the injector would probably be pretty faint.

 

Ahh yes, the infamous popcorn emoji has come to save the day, solved all my problems. Now all I'm missing is someone chiming in saying “just google”.

 

Or maybe I like popcorn while watching experts solve issues and want to know how it turns out?
Saving the day is Superman's deal. Seems like this issue is usually chewed up wiring, usually where it isn't obvious to see

 

Did you put factory NGK Iridium plugs back in? You didn't get them from Amazon/Ebay did you? I dont see an extended oil change messing up valve stem seals unless the engine is badly sludged up already.

 

DENSO FK20HBR8 (3491), manual recommended plugs and exactly what I took out. From O’reilleys…no Amazon or fleabay fakes.

 

Any narrowing down of the “hard to see” areas to try and check in this case? Im hoping someone has an idea of the routing for this wiring or known problem areas for rodents causing cylinder misfires.

 

im just talking crap about probably still driving it with a misfire cuz majority of the guys here do that with zero concern of doing additional damage cuz they dont know any better & they still have places to go......
The long rod or screw driver will work in a pinch, nothing wrong with that, you will still here the click click click....

 

Oh I'm talking crap with you, I assure you.

 

Well, interesting update. They came over today and right away mentioned the truck was running noticeably worse. More severe misses and it’s burning lots of oil and blowing a cloud of smoke on startup.

Coolant hasn’t dropped and no sign of the milkshake. I checked the dipstick before they left and they were 1.5q low. He said he had topped it off 3 days ago.

They have had oil consumption from the leaking valve seals before this, and light smoke on cold start overnight, but both have been minimal until now. Still just throwing 0304.

I think they finally listened today when I told them again they really need to not be driving this truck.

Thoughts on a head gasket? These ever blow one and have zero coolant burning off but oil consumption? Starting to think this misfire might be compression related. Would that long overrun on the oil change potentially damage piston/oil control rings?

Thoughts/Ideas anyone?

 

Pull the efi-main 2 relay from the box and put the gas pedal all the way to the floor and hold it there while cranking it over as a relative compression test. Crank for maybe 7-10 seconds with a few minutes in between to allow the starter and wiring to cool down. It should have a steady cadence to it.

If you don't know what that sounds like then try it on a known good engine(presumably your own) for comparison. If it sounds like it drops out in an irregular rhythm then pull that spark plug back out and do a real compression test or even honestly at that point i'd skip straight to the leak down test. If the relative compression sounds wrong

 

So went over today and tested for exhaust gasses in coolant for head gasket, all clear. Then did a compression test, 165psi. At this point leaning towards fuel injector. Thoughts?

 

Which one? Port or direct?

 

I have no idea honestly. Im at fuel injector because spark plugs have all been changed, coils have been tested, compression checked out, and the HG is still intact. I stuck a borescope down to the wiring harness on the injector for #4 as we always have rodent problems out here but all the wiring along the driver fuel rail looked mint. So unless theres electrical issues deeper back somewhere I'm wondering if that fuel injector might be the culprit.

 

Injector circuits connect to main engine harness via junction connectors. May need to lift the intake to see check wiring all the way to the main harness. If good, check at what engine load it starts grossly misfiring.
#4 port connects via EJ1
#4 direct - via EI1

 

Very helpful diagram, thanks. Ive never driven this truck but I do know they told me the last time it was particularly bad was when they were going up a large hill. They described it as “the truck trying to shut off”. As in a huge shudder from the motor and they thought it was going to die. Past that it’s just been described as a constant degraded performance and reduced fuel economy.

 

Based in the driving condition it is likely a direct injector. It is a pricy one and need some effort to replace it
Check if other cylinders on that bank are not misfiring. Check fuel trims.