Sorry to start a new thread on this but I'm in a hurry to get this figured out as time really is money on this one.

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?

 

I would suggest a cooling system pressure test,,,,done with engine cold.
Then a compression test . If there is a head gasket problem those tests should provide some info.
I would also suggest if you are going to do the cooling system test,and it will not hold pressure to remove the plugs before attempting to start the engine because if a considerable amount of coolant gets into the cylinder(s) it could produce a hydrolock condition because the engine can compress air , but not coolant.
You should be seeing some coolant loss, and the reservoir level going down if coolant is getting into the cyl)s) .Any high temp problems /overheating?

 

Had an overheating issue about 6 weeks ago but it never pegged too high before I got it fixed. In diagnosing the overheating I would sit in a parking lot at the end of a long road doing some testing. When the dash temp gauge got almost all the way up I'd start to drive and it would cool down fairly quickly. Been driving it steady for the last 6 weeks since the problem got fixed and everything has seemed fine.

The coolant reservoir does seem to go down slowly but I'm not sure there isn't a small leak somewhere else.

 

I've gotten the suggestion that this may be a leaky intake manifold or gasket. Is there a test I can perform that will confirm that it's my intake manifold that's leaking before I start taking parts off?

 

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

Any last advice on an inexpensive source for an OEM intake mainfold? Considering how much this car is driven I better stay away from after market.