I have a 1999 F-150 Extended Cab with the 4.6L V-8 with 143,000 miles and the 4th Cylinder is missfiring. I have installed new coil, spark plugs, and spark plug wires but it seems that some form of liquid is coming onto the spark plug like water or anti-freeze that is causing it to missfire. I have considered it being a cracked or blown head gasket but if you have anymore suggestions or information as of to the cause of this or a way to find out what it is without taking the head apart to see what it is please email me at ZXRick2004@aol.com or AIM DrEvil52005 and thank you for any help provided.

 

Intake gasket leak is a possibility. Do a compression check to see if it's leaking, then a leak down test to see where it's going. Check your coolant overflow tank with the engine running up at temp and see if bubbles are visible as well as an oily film and or exhaust/fuel smell. If it doesn't show up in the tank, it's most likely an intake gasket. My mustang had #8 go like this, it was an intake leak. #1, 4, 5, and 8 are all close to pretty big coolant ports with a rather thin layer of gasket between them.

 

Do you think it could possibly be the Heater hose that runs right over that 4th Cylinder because it does not seem to be coming from inside the cylinder, if that is possible because the liquid is on the outside of the sparkplug. I will be sure to check the thinks you suggested and maybe it will help me figure out what could be causing this. Thanks for your help.

 

start with the easy stuff first

 

That sounds like a good idea to me.

 

Those are quick connectors on the hoses going to the heater core, they are right above #3 & #4, are prone to leaking, and are a common cause for the problem you are describing.

I had to bypass my heater core this summer, and spilled some coolant into #3 & 4, had a hell of a time diagnosing the miss, but that's what caused it. If you haven't changed your coolant in a while, I would suggest you flush the system, figure out how to get the Q/D's off the core (I cut mine off since I had to replace the core and the hoses, so I got off easy - but not cheaply) and either get new o-rings for the core or cut the Q/D's off the end of the hoses and just use regular hose clamps.

Good Luck!

Jamie D.

 

That is a common problem, id check it out.

 

Do I need to replace all the hoses to the heater core to fix the leaking or can i just get new quick disconnectors on the same hoses?

 

im sure new hoses would work, but im not sure about the quick disconnectors. Since the liquid is on the outside of the plug, im thinking its the heater hoses thats the problem.

 

I have a '97, F150, 4.6L V8. I have had trouble with #4 cylinder.
It turned out to be a bad intake manifold gasket.

 

Did you have antifreeze around your spark plug on your 4th cylinder?