I am looking at buying a 2008 F-150 and the dealer told me he had his mechanic check the engine and had to replace 2/3 coil packs so he went ahead and replaced them all. It’s got about 167k miles. How big of a concern is it that the coils packs had to be replaced. Is that indicative of other problems I need to look into before I buy it?

 

No big concern at all --- except with that mechanic. Don't ever go back to him again. Because chances are 99 to 1 that there was nothing wrong with the coil packs he took off. They are the number one 'scapegoats' for parts replacements in addressing misfires, and that you should be concerned about.

Annoying misfires that return and presist after multiple efforts to fix them are an early indicator of more serious issues if you are dealing with a Triton engine. And 167k miles is entering the range of mileage for timing issues to emerge.

Not trying to scare you, just assist you in being informed. If he succeeded in quieting down some misfires, he just inadvertently cured electrical connection issues by jostled something, or replaced brittle boots which should be replaced (ALONG WITH PLUGS) anyway. But coils have NOTHING in them that is prone to fail - just two different lengths of different size wire around an iron core.

 

New coils, if they're Ford, are welcome whether they were needed or not. I'd be more concerned about the plugs being changed by 167k or not, however.

Increased resistance from too large a plug gap has been shown to burn out coils prematurely. Not saying the coils WERE bad in this case, but their rate of failure does tend to increase the longer plugs are ran.