2002 F350 178k miles. I've changed plugs, replaced the #10 COP after getting misfire code for that cylinder, replaced PCV valve, checked elbow and hose. During plug change, broke the clip on #8 that holds the wire to the COP. Still had misfire. Took back to Autozone and code showed 02 sensor, but not which one. Drove for a while that way, then went around and tightened the bolts that hold the COPs on because can't seem to get them tight where they don't turn, pushed all the wires onto the COPs to make sure they were all clicked in place (#8 of course stays loose, but snugged it up), fired up the truck and it blew a bunch of black crud out the tailpipe like a big sneeze. It then idled smooth for a couple hundred miles, then it would have an intermittent mild misfire until yesterday. I repeated the process of checking all the connections and tried to find a way to secure #8. The bad misfire is back. And now it is throwing water specks out the exhaust at idle, slightly oil-colored. Truck is not driven daily, by the way.

(1) I pulled the wire off #8 while the truck was running and the misfire got worse, so does that mean it's not the culprit or just that it's making some connection just not good enough?

(2) Can a bad 02 sensor cause a misfire?

(3) Is there any way to isolate which 02 sensor is bad?

(4) Can I test for a bad COP by just unplugging the wires while it's running or do I need to buy a new COP and change it out a cylinder at a time until I get a smooth idle?

(5) Is there something else that could be wrong?

(6) What is the dark spatter of water out the tailpipe a symptom of? Related or unrelated to the misfire?

Any help would be appreciated - when the idle was smoothed out it ran like new, so I really feel that if I can track this down I'll be in good shape.

 

(1) I pulled the wire off #8 while the truck was running and the misfire got worse, so does that mean it's not the culprit or just that it's making some connection just not good enough?

If the missfire got worse, that I would think #8 is not the cause.

(2) Can a bad 02 sensor cause a misfire?

No.

(3) Is there any way to isolate which 02 sensor is bad?

Yes, you need a good scan tool to read the voltages from the O2 sensors. From that data you can determine which is not switching correctly. Your V10 has two upstream O2 sensors. O2S1 and O2S2.

(4) Can I test for a bad COP by just unplugging the wires while it's running or do I need to buy a new COP and change it out a cylinder at a time until I get a smooth idle?

Either way is ok for trying to determine if a COP is bad.

(5) Is there something else that could be wrong?

Yes, of course. Many other things can cause a misfire other than ignition related components. I would get a hold of a good scan tool like an OTC or Snap On and have someone who is experienced do some diagnostic troubleshooting. Are there any codes set now?

(6) What is the dark spatter of water out the tailpipe a symptom of? Related or unrelated to the misfire?

If it is just water, then it is normal.

 

Thanks for the help. I did get a code, as I said, for an 02 sensor. Bought one and as luck would have it the sensor I decided to change (passenger side upstream) had a longer wire harness than the one I bought, so I went over to the driver side. Changed that one and it is idling much smoother now. A guy told me to "drive it like you stole it" afterward, which I did. Went back to Autozone and there are no codes. It still has a very slight "chugging" at idle, but I'm hoping that will get better as it gets cleaner.

I took pics of both old 02 sensors, but haven't figured out how to post them. The "bad" one has melted plastic at the plug that it took forever to get apart and the sensor itself was black. The one I put back in does have a little black on it, but nothing like the other one. If it's got any soot on it at all does it need to go also?

 

Post the actual code you received from the scanner.

Heavy black soot would be a result of running rich on that bank. Which one was it, driver or passenger, that had the heavy deposits?

An bad O2 sensor by itself will not make a car misfire. It could cause the rich condition you may be experiencing though.

 

Unfortunately I didn't write down the code when I was getting it (inexperience), although my recollection was that it was just one code. It was the driver side that was really bad. Looked like the plastic part of the harness had been resting against the exhaust and had been melted thru to the wires, and the sensor looked like charcoal. Seems kind of like a chicken or egg question to me - the problems may be related, but hard to tell which led to the other?

 

well i don't get it. truck idled great for about 50 miles or so and then the rough idle was back. how long does it usually take for a new 02 sensor to "settle in"? or how long does it take for things to clean up? i'm really frustrated.

 

Have you done spark plugs on the truck at all? Never mind, just saw that you did. Which ones did you use? How did the old ones look? Old plugs can tell a lot.

 

Hopefully you changed the sparkplug boots an used dilectric grease on them.
also you used oem plugs I hope.
If you didn't change the boots ,I suggest you do .
They crack and you can't see it which leads to arching.

the water in the tailpipe is a product of combustion ,unless your seeing the antifreeze disappear from the bottle.

Rich

 

I used the motorcraft plugs and the grease, but didn't change the boots. Is it better to determine if any more of the COPs need to be changed before buying the boots or just go ahead and do the boots since they're relatively inexpensive? I just don't want to buy 9 boots only to find that 7 COPs are bad...

 

The speckled water thing has stopped since the sensor change - forgot to mention that before. Will pick up some boots tomorrow and see if that helps, but I think I may need to go ahead and change the other 2 sensors after that.