2003 Grand marquis misfire cyl 8

Hi - I have a 2003 Grand Marquis that is misfiring on cylinder #8. I swapped the ignition coils from cyl 8 and 5, reset the codes and test drove. The misfire moved to cyl #5, so I replaced the coil. The car ran great for a day, then cyl #8 started to misfire again. When I removed the ignition coil from cyl #8 I noticed quite a bit of fluid in the chamber, partially covering the spark plug. I also noticed an exposed wire in the ignition coil connection. I taped the wire and cleaned up the fluid covering the plug and reinstalled the ignition coil. The car is running great now, but I suspect I have a leak somewhere that is going to once again get into the spark plug chamber and cause more misfiring. I'm not sure where the fluid is coming from or what it is. Looks possibly like antifreeze, but not sure.

Antifreeze present in the #8 spark plug well may indicate an intake manifold leak. I'd start by checking that the manifold bolts are properly torqued down and look for evidence of cracks in the plastic. There's a coolant gallery back there that goes into the head, so it's very possible that the manifold gasket has failed (possibly dried out and cracked from frequent heat exposure from the engine). It may only manifest itself when the engine is hot and running at or near full cooling system pressure (16psi).
I'd also check the thermostat, as it may be sticking and causing an unexpected increase in system pressure.

If a leak from the manifold is spraying on the COP at #8, it will definitely lead to a short and premature failure of the COP.

Others in the forum feel free to correct me on this one.

Thanks for the reply.

You confirmed what I suspected. I do see mosture at the base of the intake manifold near cyl #8. Looks like the gasket could be failing or maybe I'll get lucky and it is the torque issue that you metioned. If the manifold is cracked that would be beyond my capabilities, so off to the shop.

Thanks again

If the manifold is cracked, it is actually quite easy to replace. I did it several times using only a ratchet set, some pliers, and some printed off instructions free from the internet. Took me about 3-4 hours in my garage. Don't pay too much at a shop. After everything, I spent under $300, including the price for a brand new Ford Racing Performance Improved intake manifold (which is a direct fit, same thing you have on your vehicle now).

Get the engine to operating temperature and check the area around cylinder 8 after shutting the engine down while hot. You may be able to see/hear a little bit of coolant leaking. The cracks may not be visible when cold!

Thanks, I'll see if I can spot the leak and perhaps try the replacement myself.

John

A pressure test might reveal it ,good luck.

I am having the same problem except its on cylinder 1. I don't want to take the fuel rail off but its not the easiest to get a plug wrench down in there. Its also on of the narrowest I have come across. Like a lawn mower socket.