misfire help request

Well said, I am actually excited to hear what the problem is/was.

 

I wonder wjat shape the coil boots are in. I had a leaky one once. It's just a short spark plug wire essentially.

 

This was literally tyhe cause of my last misfire on my 3.4

 

I had ordered a extra coil off evibay for I think 12 bux, it came with a new boot (this is just a Chinese coil for testing) and it cleared it up. Yhen I swapped the boot and put original coil. Still gone soooo. New good boots.......now to check w/o buying I would just put tape all along the old boot to temp. (kinda semi-perm really) re-seal it and if it clears up, voila.

I think carefully peeking in the dark may show it also. That's what we used to do to check plug wires if they weren't dead was watch for arcing at night.

 

Lack of funds has put this project on hold. I compression tested the truck because so many were dead sure the head is cracked... and all cylinders checked out above 165lbs, which is close enough to spec for me not to be worried about it. Given that I'm not loosing coolant, the truck doesn't overheat, there is no milky white substances in the oil, no unusual odor from the exhaust, puts me squarely back at page one. I replaced all the spark plugs because they are cheap and it couldn't hurt to try. Metered the MAF with a DMM it checked out okay. Metered the cam sensor with the DMM both cold and hot and it is also in spec. Metered each fuel injector cold and they are all within spec. It is difficult to check them when they are hot. Metered the crank sensor cold and it is also within spec- and again difficult to check hot. Replaced all four ignition coils. No change in symptoms.

Cold start truck runs fine. Immediate restart truck runs fine. Restart after 10-15 minutes truck runs but has a miss. Code does not appear until I begin driving it with the missfire. P0301, P0304, P0300... no other codes for MAF, CPS or CrPS. The symptoms are very specific and repeatable.

What I haven't tried: moving fuel injectors around and replacing all the sensors.

 

2 of us said spark plug wire or boot. Switch them around to see if it follows. We both had same symptoms. Intermittent mis fire at temperature.

 

It is a 3rz and I replaced all four coils with new Denso units.

 

I don't know the answer to your problem but just sharing this as a way to brainstorm, think out loud, etc.
In last 20 years, outside of the normal causes of misfire, (ign related stuff), I've read about or seen 2 problems that manifest as misfires with our engines. First is coolant somehow someway getting into combustion chamber. With you not losing coolant, that's obviously not likely.
The other thing I've read about here is that with age the injectors end up leaky and drip into the cylinder when turned off. Can cause a hard start, rough start, rough idle until the excess fuel mix clears out.
To verify something like that, I think would get it to do the problem and shut it off and pull the plug that had the misfire and borescope it looking for wetness or sign of leaky injector in cylinder. There may be a better way to verify that as well. There was a big thread about it with some real good input from some master techs. I'll find a link

 

https://www.tacomaworld.com/threads...d-cranking-after-engine-swap-3-4l-5vz.354399/
Lots and lots of posts on that thread. Might have something pertinent to your situation.

 

No idea if this is related to your problem and don't want to confuse you when you may have a multi-dimensional problem.

However, I can provide some information on how to identify counterfeit injectors.

Post 12 in the following thread.

https://www.tacomaworld.com/threads...cleaned-what-do-they-do.630582/#post-21617992

Post 13 in the following thread.

ttps://www.tacomaworld.com/threads/fuel-injector-rebuild-service.637361/#post-21961315

Pintle caps on the counterfeit injectors started to melt and deform after 1,500 miles. One melted and became stuck in the intake manifold. I had to fish that out with a vacuum and pick.

Note that I did not experience a noticeable problem with the engine starting or running, I found the issue when the melting injector caused a fuel leak. Naturally, it does run better after I installed new verifiable OEM injectors.

 

And the winner is...."Good deal" post #7

I am going to drive it for a few days before I change the title to "solved" but so far it seems to be running well with new injectors from FiveO Motorsports. I ordered the new injectors before I removed the old ones just because I wanted to be able to move the truck around if I needed to. Once I removed them I could see visual signs of degrading.

I tested the injector while is was cold and got a proper resistance value of 14.2. I brought it into the house and left it on one of my cast iron radiators with the heat on. I tested the resistance again once it was fairly warm to the touch and I got an open circuit. I feel pretty confident this is my problem. BTW, all the injectors have this same sign of cracking to some extent or another.

Hopefully these new injectors are of good quality and last a while.

When I had read post #7 I had a feeling that this person was on to something. He described that he had an identical symptom and had his solution. This is what I was looking for. Thankfully I didn't waste much more time after reading that post and made the purchase for new injectors as soon as I could afford to.

 

Awesome to hear that you got it figured it out and you found your identical symptom, lmao