Help with misfire codes

[lipe1970]

Hello all,
Have a 02 limited 4.6l that is throwing 2 misfire codes on the 6 and 8 cylinder. Engine runs good at startup. After warming up, will sometimes idle rough, but not all the time. Under light acceleration, sometimes it will jerk a bit. Seems to be worse when the temperature outside is above 50 or so. Today it is in the 20's, took it out for a ride, and it ran pretty well. I'm on old school guy trying to learn about the newer cars. Read alot on the forum about changing spark plugs and coil paks, but i'm not convinced that is what it is considering the miss on both cylinders started at the exact same time. Was wondering if it could be something with the emissions systems. This is a high mileage explorer, 250,000 miles, but well taken care of, mostly highway miles. Not my primary vehicle anymore, but definitely want it running good for snowy days. Any help would be appreciated

 

[Number4]

Is the CEL on? Are these actual trouble codes or pending trouble codes? The codes you are getting, are they P0306 and 308?
Any other codes?

Just some basic questions to help others help you out.

 

[5whiskey]

I would replace all the spark plugs and the coilovers on the faulty cylinders. Why? Easy, cheap, and technically could be your issue (although it likely won't be a fire issue for reasons you stated... but it could be). If that doesn't fix it I would compression test those cylinders. Could be a head gasket. Could possibly be a fuel issue somehow... injectors maybe? My money would be on compression, especially if 6 and 8 are on the same bank.

 

[Number4]

6 and 8 are on the same bank, the compression idea was a concern I didn't want to mention, but was my first thought.

From what I've read about the 4.6 and 5.4's is that misses on 8 are bad signs. Bad exhaust valves being the issues. Though, the valve set up and year don't usually apply to the Explorer heads.

 

[lincolnshibuya]

I'd start with new plugs and cops, very inexpensive. I replaced all my cops at 140k since they started to misfire 1 by 1. At your mileage they are pretty much due for new cops.
Check also if the boots or plug holes 6 and 8 are filled with oil or water (don't replace the plugs and cops if you have this issue, it will occur again), if it's oil then it's probably valve cover gasket leaking and need replacing. If it's water it might be the intake manifold leaking and going into the plug holes or just moisture.

 

[lipe1970]

Yes, it does have codes pending p0306 and p0308. Why I think it may be some type of fuel issue or emissions issue is because it did the same thing at the beginning of the summer for a few hours one day, then was fine. Three months later, it did it again then ran fine for a while. Do coil paks short out intermittently? I've watched a few youtube videos on changing plugs and it doesn't seem to hard, especially after changing plugs in a big block 69 mustang. Thanks for the help guys, like i said, i'm an old school engine guy trying to learn about these electronic engines.

 

[Number4]

I started my 04 up the other day after having not been used much. The heater switch was set to on as well as the fan. My Ultra-Gauge alarmed me to two pending codes.
P0305 and P0316. Pending miss on cylinder 5 and pending miss on start up.
Other than the alarm, it ran fine. I'd have never known of the pending codes.
Let it idle for a bit, no further codes. Cleared codes and hasn't happened since.

I'd done my plugs a month or two ago. If it comes back, I'll start with the coil.
But I don't know what caused the pending code.

 

[lincolnshibuya]

try swapping the COPs on the opposite bank, see if the same code appears.
4.6 doesn't have coil packs, they have COPs (coil over plugs)
4.0 uses coil packs.
misfires are bad for the catalytic converters, got to fix it soon.

 

[lipe1970]

My vehicle had also sat awhile when this first started, was out of town for a few weeks and when i came back, took it to the car wash and it started idiling rough in the car wash. New fuel filter about 3,000 miles ago. Ran royal purple max clean through it about 300 miles ago. My gut keeps telling me emissions, but no code.

 

[mikeinri]

I just went through hell chasing misfire codes on my 4.0. One of the items that comes up is intake/ vacuum leak. If you're remotely wondering about that (and with those miles, you probably should be), get a smoke test done. It's the only clear way to rule that out and/or find the actual leak.

Hope this helps.

Mike

 

[lipe1970]

Thanks Mike, was thinking that myself, may try to do a quick and dirty check of the vacuum lines over the weekend, it is like 5 degrees here today

 

[mikeinri]

I did a lot of research online, and watched a LOT of YouTube videos. There are some common failure points in the vac lines, and there are some great vids showing how to do a DIY smoke test.

I agree with the others above with the idea of trying to swap components where you can to see if the problem moves with the parts, or stays with a specific cylinder.

I'm a fan of anything that is effective without blind part-swapping (buying new parts until you get the right one), which I have seen way too many times at local garages and dealers around here.

Good luck, let us know what you find.

Mike