Tacoma v6 misfire

Hey guys,

I’m out of ideas could use some help, I’m working on a 2007 v6 Tacoma and has an intermittent misfire on cylinder 4(po304). I’ve replaced coils, spark plugs, fuel injectors. I’ve also did a leak down test and it passed, I did a compression test and held around 180psi. I also did combustion leak test it passed aswell… additional verified cylinder 4 sparkplug was sparking

 

When does it misfire? Under load, idle, cold start, all the time?

Has it always been on cylinder 4?

 

If you are pulling plugs... get a cheapo boroscope camera, the kind with little LED lights, that plugs into your phone or your laptop. So you can look inside the cylinders, through the spark-plug hole. See if there is fluid at the bottom of the cylinder. You need to crank the piston down to do this.

There is an issue with '05 and early '06 head gaskets that can cause this kind of problem. But as you have an '07, this is probably not your issue. However, if this was the problem, then the engine could pass compression, leakdown, and combustion gas test -- with flying colors -- and still have a little leak in the head gasket. Enough to cause a misfire because there's coolant in the cylinder. Believe it or not.

Again, this is probably not your problem, because you have an '07. But the little camera is only like $20, which is less than injectors and coils cost, plus you can use it to look inside your walls when you are trying to fish wires, or inside your ears if you want to be grossed out. Super cool.

Compression tells you your valves and pistons are good, and you have spark... so unless you got double-unlucky with two bad injectors, this is the only other useful idea I can offer. Wait, that actually gives me another idea... maybe check the wiring to the injector? Oh, and what about the fuel pressure, is there enough of the PSIs? Okay, now I'm guessing.

Hopefully someone more knowledgeable can chime in. Good luck!

 

Swap #4 coil with another cylinder, then see if the misfire follows the coil.
If it does, Replace the bad coil.
If it doesn't, swap the spark plug with another cylinder and see if the misfire follows plug.
If it does, Replace the bad plug.
If it doesn't, start looking at ECM wiring for bad grounds, shorts, and opens.

 

Happens randomly

happens randomly doesn’t matter

 

We replace coils, it doesn’t follow

 

I actually have a boroscope I looked into the cylinder when I pulled the spark plugs I talked to a Toyota rep he thinks it could be a coolant leak he said run it for 10min and look to see if there’s coolant in cylinder, so that’s my next thing I’m gonna do, he also said I’ve pretty much gone though the list he would go through