I had my check engine light come on the other day and engine was sputtering- my mechanic scanned the diagnostic code which was #8 plug misfiring- he replaced all 8 plugs,wiring boot and ignition coil- test drove it- said it was fine- after me in it for 2 miles- the engine started sputtering again. I just paid him $450 for this and I'm right back where I started- he did say he saw some oil down in where one of the back spark plugs went in- any ideas??????

 

You have a bad coil and I bet it's #8. I'll try to explain what cannot be explained. You have a "low grade misfire" on the verge of Primary failure.

For some strange reason, a fresh re-boot of the PCM manages to fire the bad coil at first, -only for a short time before it heads right back in gutter. Not just with your model year 4.6L, this has happened many times over with 97-03 CoilOverPlug (COP) Ignition systems. Your mechanic re-booted the PCM by disconnecting the battery, -which is what your suppose to do when working on these engines.

Most likley you could get away with replacing just #8 coil (under $10 if you do it yourself), it's much better to update all your coils when they get old. Ignition integrity plays a pretty good size roll in overall original engine performance. I hope your mechanic installed Motorcraft plugs.

These are the coils you need for that model -

http://cgi.ebay.com/ebaymotors/NEW-I...ht_2539wt_1165

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The oil found in the plug chamber is most likley from missing the filler neck when adding oil to the engine. The oil will travel on top of the head and dump into the plug chambers.

It could also come from a valve cover gasket leak.

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If your check engine light is on again , - get it scanned again and write down the numbers from the scanner. Post them here. Scanning is FREE at Auto Zone.

 

that gives me some insight-weird thing is, this morning driving in to work- a 12 mile trip- the truck ran fine! it was cool here 54 degrees- so maybe once it's up to temp it may start acting up again- anyhow- the engine light is not on and things ran smoothly- I guess I'll see what it's like during the day- he did replace the ignition coil, is that what you recommended? thanks again for your help!!

 

We are recommending you replace all 8 coils. It's worth the 80 bucks. Keep the old ones for spares.