My #4 cylinder on my 5.4 has gone through 3 coils in the last year. I replaced the spark plug and coil about a month ago. Two weeks ago the "service engine soon" came on and went off two days later. Two weeks later it comes back on. I had the intake manifold replaced 1.5 years ago because it was leaking coolant, about a gallon every 1.5 weeks. Do I have an electrical problem or what? Truck has over 151,000 miles. It runs good except every 2 to 3 weeks I'm getting the service engine light.

 

Sounds to me like your heater lines are leaking coolant onto the #4 coil.

 

I second this

 

I will definitely check that out. Thanks!

 

having same issue with 01 5.4 triton
how do you know if it is the heater line of the intake manifold?
would heater line cause AC coolant to be low?

 

Not necessarily. Not much coolant needs to leak onto a coil to short it out. Check the condition of the heater hoses and also make sure the connection to heater core is good. If the quick connects where used they are prone to leaking. When I replaced my core I had a problem seating the coupling to the heater core and mine would leak. Finally got it clicked on good.

 

Well, I do have a leak but it's the thermostat housing. They said it's all dry where the heater hoses connect to firewall. Could I just be having a computer "burp" or may I be experiencing an electrical problem?. Before I replaced the intake manifold about 1.5 years ago, coolant was leaking where the engine valley had a puddle of coolant. Do think all that coolant leaking on top of the engine caused an intermittent electrical problem?

 

could have bad compression on that cylinder. what brand of coils and plugs are you putting in it? if it's not motorcraft that could be your problem.

 

Motorcraft.

 

are any coil wires broken or anything? did you put any dielectric grease on the coil boot? if you did everything right and nothings broken i'd get the compression checked. first try some injector cleaner that cylinder might have more carbon build up on it then the rest.