I have a 2010 F150 XLT 5.4L V8

I was on my way back home from a trip and when I had to speed up to get around a car my engine started bogging and my RPM's kept staying high and I got a check engine light. My head unit can read OBDII codes and the code that showed up was P0308 which I found was cylinder 8 misfire. I decided to clear the code and see if it came back and sure enough it did. I cleared the code again the next day and was going to buy all new spark plugs for my car then I got another check engine light. This time though it was P0430 code.

I have read that P0430 is usually the CAT but since I got code P0308 first is there a chance that I just need to replace the spark plug or is it likely that I also need to replace the CAT?

 

probably what happened was the misfire was bad enough that it caused the cat to start to melt down which can happen, was the CEL on solid or flashing?

 

How many miles on this engine/truck?
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It was flashing first when I got the P0308 then went away while driving, then came back on and stayed solid about 10-15 minutes later.

 

About 155,000 miles are on the truck

 

Change the plugs and COP's. Make sure there are no loose heater hoses above the engine leaking down on the engine. Disconnect battery ground cable for no less than 15 mins.

WARNING: Be very careful installing the new plugs, it's SUPER EASY to crack the ceramic insulators which will create a miss fire.

Drive for a while once the engine is running normal (no miss fire) and clear any codes that may pop. If after about 100 miles you still get that cat code you may need new ones. As it stands right now that miss firing cylinder has caused excess unburned fuel to enter the exhaust stream which can overload a well used cat.
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Thanks for the info. I will get a new set of spark plugs and replace them and drive the car for about 100 miles. If it the check engine lights comes back on and still gives me the same P0430 code would I just have to replace the drivers side CAT?

 

At your mileage replace all the COP's as well and if going by warranty life span you should already be on your 2nd set of cats. One thing at a time.
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