2003 expedition misfire no.4 cyl.
 

Hey Guys, I have a 2003 expedition 5.4L.

Engine light came on the other day scanned it and it show no.4 cylinder misfire. the guy I bought it off had new NGK plugs put in, I replaced them with ford OEM and replaced the no.4 coil as well. Truck ran great for about 3 days then SES light on again, no.4 misfire I swapped the coil with no.1 ran fine and the next day same thing. I've checked the injectors they seem fine also the hoses to the heater core to make sure they weren't dripping on the coil and causing the misfire, No leak there, also checked the plug connector to the coil as well. So I'm a bit baffled any tips would be great.

The only thing I could think it may be is the no.4 injector stuck open it does fog for a bit on startup in the morning so im thinking it just dripping into the cylinder causing the misfire

Something you can check,
the plugs that plug on to the PCM, some vehicles had a water intrusion problem there.

ya worth a look thats for sure.... Thanks

Ahhh-Sooo Master Hank ...

Most of my C.O.P.s misfire on my 1997 Expedition 5.+ liter churn, or so I think.

Based on above comments I'll have to look~see at the PCM, what ever and where ever that is.

So if water/moisture has invaded the plugs plugged onto the PCM, what to do?

WD-40, air dry with compressed air, check for corrosion and maybe a little dielectric grease? Or forget the grease? Best way to clean/dry the connections is...?

Thanks in advance skip.

What you stated with the WD 40 always worked for me!