Cylinder 7 Misfire

[02Exp.Enthusiast]

Hi, I have a 2002 XLT 4.6 with over 220 k on the vehicle. I've noticed lately that my truck has a distinct shake at idle while in drive, not park or neutral. Also, the acceleration is poor. The check-engine light was on so I used my OBD-2 readout and discovered it was a cylinder 7 misfire. So I pulled the plugs and rubber ignition boots and replaced all of them. Still, there is no improvement. Also, when I did this, I noticed that cylinder 7's plug was covered in oil, which leads me to believe that it could be worn rings. Or should i just replace the coil. Please help!

 

[Top Jimmy]

Conventional wisdom would suggest replacing the coil. There are multiple threads explaining how to test before hand, but it is an easy replacement and relatively inexpensive. The fact that is it "covered in oil" is concerning. However, if the cylinder is not firing (for what ever reason) you will see some residue on the plug. A compression test and comparison to other cylinders will help you determine if you are passing enough oil by the rings to cause a misfire. Good Luck.

Jimmy

 

[Half-cocked]

When I changed my plugs ('99 5.0L V8) at around 90K miles, the #8 plug looked oily.

A short time (2K miles?) later, it began to occasionally misfire. The culprit was a marginal coil pack - replacing that cleared up the problem, and at the next plug change the #8 plug looked normal, compared to the rest.

 

[02Exp.Enthusiast]

Since the miles are so high, does anyone think that too much oil is getting past all of my rings, but just the misfiring cylinder has so much buildup because it has little if any combustion?

 

[Rarestace]

its probably just build up from not firing properly try swapping the coil with another one to see if the miss fire moves that will tell you that the coil is bad

 

[Half-cocked]

How is your oil consumption?

 

[02Exp.Enthusiast]

it doesnt seem that noticeable. maybe about half a quart between changes (4000 miles)

 

[Rarestace]

have you tried swapping that coil to another cylinder to see if the misfire moves with it

 

[jayton]

I would be willing to bet the oil is coming from the valve cover gasket. You should at least see an improvement temporarily when replacing the plugs and boots until the oil can saturate and cause a misfire again. It must be something else. Try swapping coils, as others have suggested, and see what code it throws up then.

 

[sethmorgan]

Since the miles are so high, does anyone think that too much oil is getting past all of my rings, but just the misfiring cylinder has so much buildup because it has little if any combustion?

If you suspect worn rings, do a compression test.