I have a '97 F-150 with the 4.6 v8. It had developed a misfire a while ago so I had the truck scanned. The codes that came back were showing that the #3 and #8 cylinders were misfiring. The scanner didn't tell me what the exact cause of the misfire was, but it said the probable cause was a bad spark plug. I went ahead and replaced all 8 spark plugs. Afterwards I went around the block for a test drive... nothing changed. It's slightly better than it was, but it's still there. I triple checked and made sure nothing was broken or damaged in the process. The plug wires are fairly new, and the insides of the boots are in great shape. Can I test coil packs, or do I have to buy them and cross my fingers? Could it also be a vacuum leak? What should I try next? I'd rather not spend the money and take it to the shop. Any suggestions will be greatly appreciated, thanks.

 

Did you use Motorcraft plugs and wires? Aftermarkets don't work too well in these engines.

You can switch the 2 coil packs and see if the miss changes cylinders. However, #3 and #8 are on different packs, I doubt both are bad. The miss should change to #2 and #5.

You may want to do a compression test.

 

The previous owner has Carquest wires on it, but they look to be in too good of shape to be giving these issues; I'm not saying that they aren't the culprit, but it seems unlikely to me. I did use Motorcraft plugs, I wouldn't dare put anything else in there. I'll have to switch packs around and see what happens. Thank you for the suggestions.

 

You mention that it developed a miss fire "awhile ago" I guess this means you have been driving it like this or maybe the truck just sat or if you recently purchased the truck and the original owner changed the wires make sure the wires are on the correct coil and sparkplug location. Whoever installed the new wires may have them on the wrong coil and or plug. Also whenever you remove sparkplugs take a good look at them they can tell you alot about what may be happening. I recently (last week) had developed a miss fire on my 97 while driving. I pulled into an Advanced Auto store and had them read the code. It was #4. went home pulled the plug , it was like new but I replaced it anyway. still miss fire. I pulled the injector and since I have a box of them sitting around I changed it anyway, still a missfire. had a spare wire changed that still a miss fire. Coil next had a new spare, changed that and problem solved. I am fortunate to have spare parts so it's not a cost issue to just start changing parts. Sometimes a code will show two miss firing cyls but it may be only one as well. The original owner changed wires for a reason and it sounds like they are fairly new so maybe that can give you
a clue to your problem.

 

Problem solved... mostly. I had the truck scanned at Auto Zone, and the code P0352 came up, it said that it could be the coil, plugs, wires, etc. I did some tests and determined that it was a bad ignition coil. I went ahead and replaced the coil, and that seems to have taken care of most of my problems. The truck starts smooth, idles smooth, and accelerates fairly decent. Taking off is a little sluggish, and it spits and sputters a little, but once it gets rolling it gets up to speed just fine. Could this still be a misfire issue, or should it just need a little bit of driving to clear up? I do have a slight exhaust leak just before the catalytic converter on the driver side, could this also be the cause?

 

Lose the O'Reilly's wires; only Motorcraft are worth using. Ask me how I know.

Jim