Misfiring when cold, plugs changed

[jhz563]

I have an 06 xlt expedition with the 5.4L in it. I had the plugs changed at about 110k miles. Since then when I let it sit for two days or more it idles really rough until I get the warning light. the light has been checked twice and first it was a #2 misfire, then the next time it was a #8 misfire. I also think I can smell just a faint gasoline odor when this is occurring as well. It happened twice on Monday after the X had sat for a long weekend. This time I don't know which cylinder(s) misfired because I didn't get a chance to have the code read before the light reset itself.

it doesn't happen every day, just when it sits for a while. I never had this problem before the plugs were changed although it was starting to run a little rough. when it happens, the engine will get progressively rougher until the light comes on, and then it will smooth out. the trouble indicator will go from flashing to steady. Usually one to two days later the light goes out all together.

I am taking it back to my local garage who installed the plugs, but I don't have time to let it sit there for a few days. Also I don't think he has a clue as to what is wrong with it. Any ideas appreciated.

 

[black 4x4]

If you just replaced the spark plugs but not the coils that could be the reason for the misfire. Also just because the cel light is out doesn't mean it reset itself. Codes are stored in the memory.

 

[steelnewfie]

I've been working on random misfires since my plug change (06 EB) a couple weeks ago as well. Also had the strong smell of gas. BEFORE you go out and start buying new coils, I'd ask the garage to clean the threads where the plugs go in with carb cleaner. I think the spark is arking after the plug change due to the infamous carbon buildup around the plugs of these engines. Also make sure you put new boots and springs on the coils.

There are numerous threads on this forum about misfires. But if I were you I'd pull all the plugs and clean the threads of the head where they screw in with a wire brush. If that doesn't cure it you may need some coils.

Stick with Motorcraft plugs (sp515) and coils (dg511).

Update the thread when you make progress!

 

[docraymund]

Time to get your hands dirty and invest in a few tools.

Check the air cleaner if its dirty.
Check the fuel pressure with a fuel pressure gauge.
Try to have the fuel filter replaced.
Have the catalytic converter checked.
Clean the MAF sensor with a suitable cleaner.
Check for vacuum leaks with a smoke machine.
Have the codes read again .

 

[Bedrck47]

I am taking it back to my local garage who installed the plugs, but I don't have time to let it sit there for a few days. Also I don't think he has a clue as to what is wrong with it. Any ideas appreciated.

Why would you take it to someone that you feel doesn't have a clue as to what is wrong with it.

Suggest you take it to someone that does have an idea what is wrong.

 

[jhz563]

thanks for all the feedback guys.
As to working on it myself I'd love to- but with three kids and an hour commute there just isn't time.

As to taking it back to the same garage, this is the guy who installed the plugs. It didn't misfire when turned it over to him for the plugs and now it does. If the problem was caused by something he did or didn't do during the plug change its his responsibility to make it right. I can take it elsewhere and then I am guaranteed to pay out of pocket. If he can trouble shoot something related to the plug install then he eats the cost. I believe he is honest enough to tell me what he finds. I have kept him in the loop about the problems since they began. I want to give him at least one chance to find and correct this before sinking more money into it elsewhere.

 

[jhz563]

steelnewfie, did cleaning and reinstalling make your misfire and fuel smell problems go away?

 

[Bedrck47]

Ask your mechanic if he changed the boots when he changed plugs? If he didn't I would recommend new boots and also use dielectric grease on the inside of the boots. Ask him also to recheck all connectors to make sure they are fully seated and also use some dielectric grease on the contact areas. And make sure all plugs were at the proper torque value.

 

[jhz563]

took it back to shop that worked on it originally, and of course they couldn't find a thing. #8 cylinder misfire code was in pending, but that is no surprise.
I haven't had the check engine light come back on, but once again after it sat for a couple days over Christmas, I got a strong fuel/exhaust smell in the cab. strong enough that I was opening up the windows. This got better as it warmed up, or I just got used to it.
Since the #8 had the code, he did switch the coil pack from the 8 to the 7, that way if the problem moves we can nail it down.

Also, in reading this and other forums I see lots of notes about rough idle and exhaust smell. Based on this I am going to go over my hoses, looking for a problem in the 90 deg boot. Also there was an f-150 forum that said the exhaust smell may be coming from some sensor port in the exhaust near the fire fire wall.

It was still idling rough this morning, but no actual misfire. Mine idles about 550 or 600 rpm, that seems to be normal based on what I am reading - feel free to correct me.

 

[steelnewfie]

Removing the plugs again and cleaning everything up did get rid of the random misfires yes. However I still have the 'rumble strip' at 55mph and intermittent rough idle. Runs PERFECT at 70 mph or 45 mph. Clean the threads of the head and only put dielectric grease where the guys on here say to.

I'm pretty much done bringing it in for this problem again unless I get some new misfires. Come spring I will pull all the plugs again and do another clean.

-15 here today. Both drivers and passenger doors froze. Would not latch shut. Any recommendations on how to ice proof? Where to treat?

Also going around a turn yesterday and heard the grinding of which I assume to be my IWE. Put it in Auto4WD and went away. Looks like I'll be investing in a new solenoid and a couple wheel lock assemblies.

Sorry for the late reply, xmas and all...