Cold start misfire

I’ve got a 2010 Tacoma with the 4.0. On a cold start I have a cylinder 4 misfire. If I restart the truck the misfire is gone and the truck runs smooth. I’ve replaced the plugs, swapped coil packs, checked for vacuum leaks, check the fuel pressure. Any suggestions on where to look next?

 

Pull the plug on a cold engine and look for coolant or fuel in the cylinder.

 

Alright, I’ll check it in the morning and see what it looks like.

 

Do you have a slow loss of coolant also?

 

Welcoming to TW

 

Also look for pooling oil at the low spot where the piston top meets the cylinder wall. A bad valve seal can allow oil to drip into cylinder overnight and this can cause plug fouling at startup that quickly burns off and starts firing again. The head design leaves a pool of oil at the valve stem (likely why the solid lifters / caps can go 200k without any wear and need for adjustment), so a failed seal can cause this type of problem. Alternatively, if you don’t have a borescope, start cold engine for only 5 - 10 seconds and shut down. Pull #4 plug and see if it is coated with wet oil. When this happens, you typically get blue exhaust for a minute or so after start up.