I have an 09 FX4, has 157xxx miles on it and I just had a spark plug change, obviously motorcraft and I feel as if the truck idles a little rough only when in Drive and at a stop light or something. 2 days ago I got a check engine light and it was a misfire on #7, so my dad bought another COP and put it in. It ran fine then. Today it kinda ran rough again but only when its not at operating temperature. Once it does reach it, it idles fine I guess. I ordered 8 motorcraft COP's anyways just to make sure. Who knows what kind of COP's I have in the truck. When my dad did the change the plugs that were in there were NGK. So anyone with any other ideas as to why I may be getting this rough idle. I'm just assuming it's the COP's are old and can't keep up with the new spark plugs or something, I guess I will find out on Monday when I get them.

One more question: Since I got the truck at 153k, I've been putting Motorcraft 5w-20 FULL SYNTH in. My dad says that's only for a new truck. Should I be putting thicker oil in because of the fact that this is a 7 year old truck with 157k miles on it or should I stick to what the cap says.

Any help is appreciated and I thank you in advance.

 

Stick to the Motorcraft spark plug specs listed in your manual, not after market. That's more than likely that's part of your idle problem. Same with the oil, your manual probably lists both (5W-20) synthetic blend or full synthetic like my 2011 F150 5.0 does. I use the Motorcraft Synthetic Blend since my local Walmart sells it along with the Motorcraft oil filter. If you're not having leaks, full synthetic is fine. That's what your dad's concern is, leaks. Some owner's I've read on here use either the Motorcraft Full or Synthetic Blend or Pennzoil's Platinum Full Synthetic, all still use the Motorcraft oil filter. Use the synthetic blend if you want a little thicker. Info in owner's manuals are engineered facts for the best performance. Stick to them IMO.

 

Yeah I go all Motorcraft lol. So should I stick to the 5w-20? or...should I get a thicker oil? and should I use synthetic blend instead of Full Synth then?

 

Just to clarify, an oil listed as 5w-20 has 5w-20 viscosity, whether it is conventional, full synthetic, or a blend. That code means that the oil is certified to meet SAE specifications for that particular viscosity. A synthetic oil won't be any thinner. Likewise, a conventional oil won't be any thicker. Synthetic oils simply have more additives and less impurities.

 

I guess maybe I confused you guys, I meant like rather than 5w-20, I use like 5w-30 or some other

 

So, I got all new coils yesterday (Motorcraft) and today I drove the truck, I stepped on the gas a bit and CEL started to blink. I'm going to assume another Misfire...If so then what is the problem? I have all new plugs and coils, I never had this problem before changing them..

 

The problem originated after your plug change if I read that correct. The problem is your plugs and or the coil pack connection.

Pull the plugs check for combustion color uniformity. Check/verify the plug gap. Which cylinder indicates misfire now? #7 or another cylinder? If the problem is #7 again check that the plug is threaded correctly, seated correctly, the coil pack connection is secure. If the problem persists, swap the plug and coil pack with another cylinder, see if the problem follows the swap, or stays with the #7 cylinder.

Use your vehicles recommended oil weight. Doing otherwise your attempting to correct a issue that doesn't exist, and or you have nothing scientific from an engineering perspective that validates the need for 5w-30.

 

Yeah it started after the SP change. I'm having my dad go drive the truck to get the CEL light on so he can check it with his tool. I guess we will see from there. I will keep you updated and thanks for the response. Also, the CEL doesn't come on unless I really step on the gas. Also on cold starts only, If I put it into reverse, I get this vibration or something as I back up.

 

Update: My dad drove my truck after I got home, and he said he stepped on it but no CEL came on....the truck was already at operating temperature so this is only happening before the truck reaches operating temperature. He is going to take the truck to work tomorrow and maybe he will get the CEL on as he is driving...we'll see.

 

Glad you said it I was biting my tongue