So I have a 4.0l that is misfiring. It started out as a bad spark plug and I changed that and it went away... for a little bit. The thermostat housing started leaking a few weeks ago and I am yet to change it I just haven’t had the time but I’ve been keeping up on the coolant. Do you guys think that the coolant leaking onto the block could have anything to do with the misfiring? It comes and goes sometimes it’s awful and sometimes it will miss 1 time in 20 minutes. I’ve checked everything there is to check and was just wondering if coolant leaking could have anything to do with a misfire somehow?

 

Have you checked the plug wires? What was bad about the spark plug? A coolant leak could cause a miss, it just depends where its leaking and on what.

 

I assume its a 2001-2011 Ranger with 4.0l SOHC engine????

Not a 1990-2000 4.0l OHV engine

The 4.0l SOHC did have issues with cracked thermostat housings, good read here: https://howtoreplacefordthermostathousing.com/
This thermostat housing is on the TOP of the intake so coolant could leak into an injector o-ring or intake air passage, if either also had a leak
On a 4.0l OHV that wouldn't be possible

+1 on the which spark plug was bad, 1 to 6, and what was bad on it.........cracked insulator, or fouled