P0308 now clear but engine runs rough

[ROBinGa]

So suddenly the 2003 4.6 started running rough this morning and CEL light comes on and starts blinking while my wife drove it. She told me about it so I took to parts store to connect thier scan tool. Codes came back p0308 and P0316 - misfire on cylinder 8. I had changed all plugs to Motocraft about 10,000 miles ago. So I decided to buy one plug and change the #8 and see if that helped. I took it out and plug had a little oil on it around the ceramic but the gap looked in great shape. The boot was a little grimy but not terrible. I cleaned everything boot included and put a little fresh dialectic on spring and installed the new plug gapping it to .054. Snugged everything up and reconnected battery. The engine started and seemed to run a bit better and immediately the CEL goes away. But when I drive for test drive it studders a bit at low speed and take off. It's still missing but CEL went away. I took back to auto parts and they said no errors and all statistics look perfect. But it's not running right, I can tell. They said maybe it's bad gas. but there was a blinking CEL and P0308 and P0316 which designate misfire in cylinder 8 and now no codes. I decided to order 8 new boots and swap out these originals that have 135,000 on them and will try that. Any other ideas?

 

[Joe in NY]

You need a new coil pack for cyl 8. Simple. Go to advanceauto online, pick the BWD (best) coil and google 30% advance coupon and do a store pick up. Cheap, best part, and you have it that day.

 

[Number4]

Move the coil to another cylinder. Wait and see if you get a misfire code on the other cylinder.

Edit: read up on this article.
http://www.motor.com/article.asp?article_ID=1794

Ford requires a hard miss or catalyst damaging misfire to throw a code. So watching the raw data, you can see if you are having misfires that are deemed 'okay' but wouldn't be picked up by the likes of AutoZone.

 

[ROBinGa]

Great article Number4. That explains a lot and the article might ought to be a sticky to explain CEL codes or lack thereof. I bet my engine had not been driven enough yet to record enough events and also I am below 15% fuel level right now. The examples in it describe my issues. I probably will go ahead and get a coil to replace number 8 cylinder. Thanks

 

[lincolnshibuya]

4.6 v8 doesn't have coil packs, each cylinder has a coil on a plug (COPS)
coil packs are for the v6 (you replace the whole coil pack when any one of them goes bad)
I replaced all my COPs right at the mileage because it started to misfire one by one. I bought the yellow ACCEL cops, so far so good and it's cheaper to.

 

[anthonymtz]

They are actually called ignition coils, each individual cylinder has one with a wire harness connected for spark timing and ect. The 4.0 v6 has one (coil pack) with 6 outputs that connect to spark plug wires numbered to match each cylinders accordingly, now for the ignition coils I would replace all 8 of them just because the vehicle has over 100k miles on them, I have seen a set of 8 motorcraft ones on ebay for about 60-70$ and some other ones that claim "15% more efficiency" and "High performance" at 45-50$ for a set of 8 in colors red, yellow, blue, green and black.

 

[Joe in NY]

Just stick with OEM or BWD. Best you can buy.

 

[Number4]

OEM is typically aluminum contacts whereas aftermarket premium is brass. Aluminum corrodes with exposure to air.

BWD is produced by Standard Motor Products, as is NAPA's Echlin line. There still may be a difference between the two. See where they are made. What I would do, is get the Denso coil from NAPA, as it was the OE manufacturer. Again, after Denso will be better than OE Denso.

 

[ROBinGa]

Yes I am aware the coil is individual to each cylinder. I just took the one off for cylinder 8 and replaced that plug, cleaned the spring and boot then reinstalled. As an update.... The engine has smoothed out and is running just as it should at idle and while driving. The CEL did not come back on after the replacement of plug #8 but it did run roughly. But after my wife drove it this morning without me knowing she was taking it she said it began running much smoother while she was queuing up in carpool line at school. I have driven it too and it's back to normal and running well. I do have the set of 8 boots and springs on order from Rock Auto that I will go ahead and swap out next week. I priced the COP at Advanced and I can get the actual Motorcraft one with the 30% coupon disc for $46 and was going to order that for in store pickup but right now I'd say not needed. I did drive to Advance to pick up the fuel filter they had to get from another store and drove the Explorer to get it. Round trip about 8 miles and had hills and stops albog the way and engine ran great. I changed out the fuel filter just now - what a pain that was. Way more difficult than my F-150. I am thinking the computer needed to adjust the drive cycle since I disconnected battery and new plug. All I know is right now I have no CEL and it's running smooth. Put in a tank of BP gas and all seems good. Will report back if anything changes