180,000 mile 5.4 supercrew. (many many to go)

changed original plugs about 15,000 miles ago with motorcraft SP479s

ran good for a while, miss came back.

changed COPs with globals.

ran good for awhile, miss came back.

The light cruise miss came back and eventually developed into a hard miss at start up before the engine warms up, and anytime under hard aceleration.

changed fuel filter. No effect.


engine threw a code for no. 7 misfire, I swapped 5 & 7 COPs and waited. NO 7 came back about 3 weeks later.

This engine is stingy with codes.

Unfortunately this is our only vehicle. Thanks for helping

 

check the plug

 

Yea, plug could be cracked or caked up w/grease on top preventing contact - intermittently. I would also compression test, just to make sure that cylinder is healthy. Low compression can be causing the issue. There's other possibilities that get more complex, but that's a few common ones.

 

Replaced this SP 479 with a new SP 479.

I would have thought this plug would have been fouled. but I've been stumped before on this engine.

For now the engine is running 100% better, why? I'm not sure.

Until next time, thanks for the help