Hi,

2003 F150 XLT 4x4 4.6L engine, 92K miles

I have been battling error code P0306, Misfire on Cyclinder 6 detected. The truck is jerking while I drive and I have a rough idle. Here is what I did:

1. Replaced all spark plugs - still got same error
2. Swapped COP 6 with COP2 - still got same error
3. Swapped Injector 6 with Injector 7 - still got same error'

The jerking occurs generally AFTER my truck has warmed up, about 5 minutes of driving. The jerking is also sporadic, normally with some heavy jerking for maybe 10 straight seconds, then it peters off and seems to hiccup for a little bit, then maybe after 2 minutes, it happens again, etc.

Also, I noticed that if I have my foot lightly on the gas, the truck seems to run rough while it's lightly pressed.

What's next? I don't want to do anything that takes all day to do or is too difficult, I'm not that great of a mechanic. I do have people that can help though.

Tom

 

I had a problem like this for 2 years because I was to cheap to change all the COPS. I changed out a bad one and then I had the problem again. I never got any service lights either. I have a code reader and everything was good . I fought this for 2 years until one day the engine quit. I had it towed to a garage my buddy worked at and when he started it it started right up. We were looking to change out instrument clusters and all sorts of things. I took it for another test drive and while driving 1/2 the instrumentation cut out. I drove back and without turning off the engine I had him hook up a black box and record which cylinder was bad while we drove. I saw which cylinder it was and decided to change out all the COPS. Never had a engine problem since. The key is that it never showed up as trouble on the service light.

 

Have a compression check done to rule out a cylinder ring or valve problem.

 

Ok, I'll get a compression test done. I'm debating if I do it myself or go to a dealer. In the mean time, is this causing damage to my truck?

Also, I'm wondering if it's the wires running to the COP that is bad. Could this be a bad wire or ignition coil?

One last thing...I'm going to pull plug 6 and see if it's wet. If it is, I am going to keep plug 6 pulled and crank the engine which will hopefully clear out any liquic that may have gone in there (when I changed my plug, there was moisture in the spark plug well). Could that be an issue? Would that be bad to do?

Thanks,
Tom

 

I just want to pass on some info that I saw on an autotech ezine -- I forget which one.

The claim was that sometimes Ford COPs failed in such a way as to cause electrical noise. This would cause a DIFFERENT cylinder to misfire. It might have been something along the lines of it caused another cylinder to fire early enough to screw it up when it got its actual trigger.

Just something to think about. I lurk around here, and I've been interested in the COP situation. I've seen more than one post where the COP that fixed a problem was for a different cyllinder than the one showing in the code. This was usually attributed the wrong code being set.

Just my.02.

 

It certainly could be a broken wire at that COP. BTW, moisture in the spark plug well is not good either. It will short out the plug and cause a misfire. If you find that again, I would start looking for where it is coming from. Good luck!

 

If you have a bad coil it might trigger a warning light. It can short and cause problems with your computer. Anything can happen then. Why don't you go to the dealership and drive around with a flight recorder.

 

I bit the bullet and bought 8 new COP's (from ebay). I decided to just start replacing stuff... However, I do want to know this:

If I pull out the spark plug and try to start the truck, is this going to be a problem? I think some of the fluid may have gone in that cylinder and I just want to clear it out.

Also, when I pull the plug and it is wet, how should I dry it? They are all new plugs.

Thanks for the help,
Bunggo

 

I wouldn't run it for more that a minute with the plug out. It will be very noisy and rough running that way but it will certainly blow out any moisture that got in there.

If the plug is wet, then what is the wet from? You might have to replace that plug with a new one. Are you using Motorcraft plugs? Good luck!

 

You nailed it on the head! I kept getting a code P0306, misfire on Cylinder 6. When I took off COP 7 to replace it, there was a huge piece of fuzz or something on the spark plug...how in the hell it got there, I don't know. Since I bought the new COP's ($80 on ebay) I decided to just use them and the truck is running great now.

Thanks for all the help and ideas!
Bunggo

 

What are you calling the (Coil on Plug) COP? The spark plug wire and boot?

 

A COP is a Coil On Plug. Each spark plug has it's own coil that is mounted directly above it which incorporates the spark plug boot. This is an aftermarket COP.

 

are aftermarket any good? (I guess that's like asking what oil is the best)

 

after market COP is fine. You can get a set on e-bay for about $80.

 

I have the similar problem on a 2001 F-150, 4.6, 2whl, 110k miles. Was getting very bad jerking when accelerating, especially at low RPM (like after it shifts to next gear). Last week I finally took it to the dealer. They replaced COP and plug on cylinder 1, $381 dollars later and it ran fine for 4 days. Then a few days ago it started to jerk every once in a while when accelerating, but then today I could barely make it up a hill with so much jerking. I took it back to the dealer and they told me it was now cylinder 6 coil gone bad and want $235 to replace AND mentioned there was browning in that cylinder signifying some water there????
I asked why it didn't show up on diags last week but no solid answer worth mentioning here... my thought is to replace the plug and coil myself for $63 but after reading some of these posts makes me wonder if we are guessing and if cyl 6 is really the issue. I searched ebay for the coil set but nothing there but one used set....
any suggestions would be appreciated.. thanks