Hey guys I've done some searching and tried different things but can't seem to figure out my problem. I have a 2004 lariat 5.4 with 140k miles. A few weeks ago I got a misfire and a code for misfire cylinder 7. Spark plugs had been changed at about 100k so I knew that wasn't it. I thought maybe it was a COP so I switched 6 and 7 to see if the code followed it. After I switched them, and at the same time replaced air and fuel filter and cleaned throttle body and MAF, the problem went away. I thought maybe I just had a lose connector to the COP that got fixed when I switched them.

Now last night on the way to work and on the way home this morning it came back. However, it threw no codes this time so I don't know if the misfire followed the COP that was switched. I figured I might as well replace it, so I headed to the parts store. No more misfire on the way there! What the heck is going on? I checked all the connectors and they seem tight. Anyone else have a misfire that comes and goes like this? I figure I might as well replace all COPS but can I do damage to the truck if it comes back while I'm waiting for them to ship? Sorry for long post but I wanted to get all the info out there to receive the most beneficial advice I can. Thanks guys

 

Nobody has ever had this problem? Or at least a suggestion, tip, warning, anything?

 

I'm currently dealing with the same thing. Mines on cylinder 4. I would just replace all the coil packs and see if that works. Where did you order them from?

 

I ordered them from global automotive on ebay. I ordered 10 as I've heard there is a chance of getting 1 or 2 bad out of the box. Is your misfire coming and going like mine? It just seems weird to me.

 

Well its hard to explain what mine is doing. I think mine is more internal but not sure yet. I have a thread about mine miss firing. Right now it is random but haven't bought a new coil pack for it yet to see if it is a bad plug.

 

i am having the problem also in my 07 fx4. changed all the plugs, and cops, but still get that "jerk" between 45 and 50 mph in overdrive only

 

Did you put dieletric grease on the end of the coilpack boots? Are all the spark plugs torqued down? Double check all connections to the coil packs. I found one of mine to be loose but it wasnt the root of my problem. Just something that I didnt check when I replaced it on the side of the interstate.

 

i put dielectric grease on both both sides of the boot, dealer changed the spark plugs, but it would be easy to check them out to see if they are torqued right, all the connections seemed tight when i plugged them in, but i'll double check that when reinstalling them after checking the plugs

 

A coil is the usual suspect. Assuming that the plugs were properly gapped when installed. Sounds dumb, but I've heard too many dumb-*** kids at the parts stores tell people that their plugs are "pre-gapped" when in fact almost all plugs aren't. Even the Motorcraft plugs.

 

I had the dealer do the plugs just because of all the horror stories I've heard. They tried to get me to do coils at the same time but I figured I could do those at a fraction of the 50 dollars per cylinder. I would hope the dealership would gap the plugs right. Hopefully my coils will be in and installed on christmas eve (my next day off) but with what could become another 3 weeks between misfires I'll have no idea if thats the problem. I just can't figure out why its so random. With the new plugs at only 30k on them would you guys see a minimal chance of them breaking on me? If the coils don't fix it that might be my next option and I'd rather make sure its done right.

Another thing is when my plugs were going out I would only feel a misfire around 50-60 mph. This misfire is at idle and any type of speed.

 

Anything can cause a misfire, but if the only code you ever had was a cylinder misfire, it's most likely a coil. I wouldn't worry about it until you get the new coils in. I also wouldn't drive it until you get the new coils in. Driving with a misfire can clog your converters and cost you a lot more money. Not to mention fouling a plug.

 

How can you tell if you have a fouled plug?

 

Hey guys please don't flame me for this but its something I've never heard of. I was talking to a guy at work and he suggested maybe it was my new muffler that was causing this?? I put a flowmaster super 10 on my truck a couple weeks before the original misfire. He said the engine might be adding excess fuel now. Is this a possibility?

 

Un likely. The pcm get the exhaust info from the o2 sensor mounted in front of the catalytic converter. changing your muffler shouldn't affect it at all..

 

Alright thanks man. I wouldn't think it would affect it with as many people there are out there replacing their mufflers.