I have a 1997 Ford F150 4x4 4.6L 220,00 miles that keeps coming up with the #4 cylinder misfire code. The mechanic has replaced coil pack, wires, plug. The heater core was leaking and that was replaced along with the hoses. With that being said it is still coming up with the same code #4 cylinder misfire. I can pull the plug boot and the boot is wet and the top of the plug is wet also?????? The last time the mechanic worked on it (replaced the heater core hoses) he told me I had a intake manifold gasket leaking .....CAN THIS FINALLY BE THE ANSWER TO MY PROBLEM?????? any help would be greatly appreciated!

 

It could be a intake manifold leak but most often its a coolant leak at the heater hose/tube connection directly above the #4 sparkplug. I know you checked and its not leaking right? Well I checked mine as well and it did not appear to be leaking but when I installed two clamps to that hose the problem stopped and when several friends of mine did the samething their #4 missfire problem stopped as well. Also pull the sparkplug boot and clean/dry the sparkplug and boot real good before reinstalling.

 

If your manifold gasket was leaking back there I would think you could see it. I had to replace my manifold gaskets just recently and double clamped my new heater hose and I havent seen a leak yet. At 220K you might as well change that gasket.

 

I had the heater core replaced last April and no problems until around October one of the hose clamps came lose and started leaking causing it to misfire....fixed that leak and still had same problem about 2-3 times a month.......#4 cylinder would misfire! 3 weeks ago it misfired again so I pulled boot & plug to dry off and noticed that heater core hoses was cracked and LEAKING ALOT. I had both hoses replaced last week and it' still misfiring
?????? Mechanic said it had a small intake manifold leak!!!!!!! Basically I just want to know if this could actually be what's causing it to misfire??????

 

Yes. And quit yelling, we didn't do it.

 

Simple, If its still missfiring and the plug and boot are dry then change the sparkplug and even the plug wire/boot. If it still gets wet with coolant after you changed the hoses and you are posistive the leak is not from a bad/weak hose clamp then you have a manifold gasket leak. Change the manifold gaskets.

 

Fold up a paper towel and use a twist tie to secure it to the heater hose. Drive it awhile then remove the paper towel, if it's wet then it's leaking. That leak, when small, is hard to detect, the paper towel will hold the moisture to tell the story.

Just a thought, good luck.

 

Yea, if it's a core hose, they don't usually leak consistently. Makes it hard to detect. They leak in pressure spurts, then stop. Sometimes making it very hard to find.

Also, look at your intake stem insert. - Not where the hose connects, but at the stem connection to the upper manifold itself. These can leak the same way , specially if it's been bent.

 

Yes. And quit yelling, we didn't do it.

Sorry If I came across as yelling! Just frustrated from trying to figure this thing out! Heater core & hoses are definately not leaking.....I will just go ahead and replace the intake manifold gaskets and hopefully this will be the end of the #4 cylinder misfire! Thanks for ALL info!