My '11 Crown vic with 270k miles suddenly started running rough mostly at the lower end of the gears. By the time you got into o/d the whole car shook. Scan tool gives me P0307 cyl 7 misfire, and P0316 misfire upon startup. So I pull the coil on 7 to find a pool of burnt smelling coolant about 2" deep. Siphoned and blew it out and removed the plug to find it's electrodes fouled with a thin coat of something shiny and black. Rubbed off without much effort. The plugs are about 4 weeks and 1500 miles old. Pulled cyl 6 coil right next to it and found a lot of white particles about half the size of rice stuck to the sides of the plug well walls. Seemed odd as I'd just blown out all the plug wells a month ago. Blew it out again and removed the plug to reveal electrodes that were coated slightly white. This plug had a ring of a black just south of the hex part. Looked like darkened sort of coagulated oil. Wiped off easily.

The car drives much better now after blowing the antifreeze out of the plug well but the miss is still there. So glad as this might buy me some time to get this figured out.

I'm not even sure how it's possible for coolant to get in a plug well. Any ideas, head gasket maybe? What's my next step in investigating?

 

my 99 would do this every 6-7 months.
i would just pull the cop and blew it out as soon as i felt a misfire.
did that for 6 years until the intake cracked.
after changing the intake i never had to blow out the plug holes anymore.

 

Good to hear this might not be so bad then. Would you recommend using some kind of leak stop additive?

 

you could try it, but my experience with stop leak additives is they tend to plug up everything except for what you want them to.

 

I've now gotten advice that my 4.6 engine has a known problem with leaking intake manifold or gasket. Is there any way i can test to make sure i have a leaky intake manifold for sure before I start taking parts off?

 

Thanks for helping a stranger everybody. Found the leak at the front driver corner of the intake manifold. Really wish it wasn't so cold out now.

Any last advice on a cheap place to get a OEM intake manifold? Considering how much this car is driven I better stay away from after market.

 

there really only are two ford, and dorman. they cost about the same.
ford manifold for $196: https://www.tascaparts.com/oem-parts...02bC12OC1mbGV4
and you can get a dorman manifold off evilbay for $175

 

 

nope, one piece manifold.

 

Ok that's what I figured. Was just hoping.

 

yea, 99% of the intake issues on the car 4.6 engines was the passenger front sensor blowing out, or the water jacket cracking rite at that sensor. the aluminum water jacket was supposed to eliminate that issue. to an extent it did, but the leaks that developed over time never stopped.