Misfiring cylinder

I recently brought my '04 Tacoma, V6 , 3.4 L engine to the shop due to it misfiring. We diagnosed the 4th cylinder as the issue. We have swapped out the coil box - no change, the spark plug - no change, the fuel injector - no change. if anyone has any ideas as to what this may be, it would be much appreciated.. I'm going a little crazy not having my truck for a week

Thank you in advance,
~Kels

 

low compression or valve issue

 

You need a compression test, wet and dry, along with a leakdown test.

It's also possible to have a leaking headgasket quenching the flame front, but the compression test should reveal that. Or a borescope to see what the top of the piston looks like. All shiny may = steam cleaned. Any other signs there may be a coolant issue? Coolant loss, running hot?

 

I did not see it in your post, did you try a different plug wire on #4?
I am assuming you did. Also a little tip from when I was
an auto mechanic years ago we use to take short pieces of vacuum hose and put one
end on the spark plug and the other end into the plug wire. Take a test light and clip it
to ground then with engine running touch the probe on the piece of vacuum hose which
will in turn cut the cylinder out. And no you won't get zapped, we did this for years.