1999 F-150 XLT V8 4.6L


Hey all,


Spent a lot of time researching my problems here, and have found a wealth of helpful info, so first off, thanks.


Long story short: after going uphill or driving with a heavy load, my girl would struggle in what seemed like second gear or in low RPM, and I noticed the CEL either blinking and going off, or staying on only to turn off a day or so later. It also seemed like I was going through more gas, even though I couldn't smell any. After spending a lot of time on here, I realized it's probably a soft misfire due to a bad coil, contrary to what AAMCO says (let us pull your transmission down and take a look for $700).


Because the CEL would go off after a while, I decided to go uphill to get the light on so I could read the error code... P0306, cylinder 6 misfire. Now that I'm almost certain it could be either the plug or coil on cylinder 6, I'm not finding the information specific to my 1999 4.6L V8 F-150 to change those out.


Can anyone advise me through the process of replacing the coil and plug, or perhaps just the coil, on this engine? I'm getting mixed info from the internet, such as order of cylinders, coil pack vs single coil, etc.


P.S.: I've also read that the upper intake might be plugged up.


As always, much appreciated.

 

I believe the 1999 4.6 uses 2 coil packs and spark plug wires.

#6 is the second plug back from the front of the engine on the driver's side. If you have more than about 60k miles on the plugs, I'd replace them all, and if the plug wires have more than about 100k or 10 years on them, I'd change them too. The coil packs seldom go bad, but you can physically switch them and see if the miss changes cylinders.

Use only MOTORCRAFT parts.

 

I want to express my appreciation for this site and anyone who replied by following up with the situation of my 1999 F-150 v8 4.6L with 230k mi.


The symptoms I had (struggling under load, lowered gas mileage, shaking uphill, and finally a check engine light with a P0306 code indicating a misfire on cylinder 6) led me to narrow down the problem to a bad coil.


Initially I thought it was a C.O.P, but it is in fact, on this truck, a Coil Pack. I went to Pep Boys and bought a new pack for $80. Before leaving, they advised me the problem could also be an ignition module or spark plug or boot. Unfortunately they don't replace a single spark plug. Instead they can only do a Tune Up, which costs $450.


So I went home, looked up how to replace the pack on youtube, and went to work. I removed the four screws holding the pack in place, kept note of the wire order of the timing plugs, and after about 30 minutes later, had the new pack installed.


I fired up the truck, and took it for a drive up an uphill highway...


Wow, I was blown away. It was like I had a new truck! I floored it and flew past the other traffic while in disbelief. A few weeks earlier I was prepared to fork over $700 to AAMCO for taking out my transmission and simply "take a look". Then I was almost coerced into giving Pep Boys nearly $500 for a Tune Up.


Bottom line? $80 and 30 minutes of elbow grease, and I've got a new truck.

Thanks to this forum.

 

It was most likely the plug / wire. If the pack goes bad, you usually lose 4 cylinders. I hope you got motorcraft platinum plugs!!!

 

So lots of info I feel lost now...bottom line are AC Delco could junk like fake China stuff or good?

 

AC Delco what?

 

I saw some AC Delco Coil Kits (8 pack) on Amazon


Searching for Motocraft also saw Delphi with AC Delco but not sure if that is the saame thing. Interestingly none of the parts for AC Delco Coils came up on the AC Delco website searching the parts numbers listed that I saw on sites. Like AC Delco BS-C1541, Delphi GN10182. So not sure if AC Delso really makes them. You can find ford parts from AC Delco so it may be reral on Amazon etc. But I appreciate the DG511 as I was certain they were straight but you gotta watch because even rock Auto, Oreilys will show cuirved boots and short plugs for 2 valves. Im creating a "contact" for my truck in Outlook formt eh info I am learning so I remember later.

 

For the price they should be okay. Denso makes the Motorcraft coils.

 

Hey guys. I have a very similar issue. Truck is still running, but half power. It’s an 08 expedition 5.4L. I found the misfiring cylinder, pulled #8, and it was burnt burnt, like melted metal and everything.
but It still runs. I can seem to make it worse.

so I tested ohms thru the coils, and I had an issue with them before. Seem i have no resistance thru the secondary coil on any of them. They’re wide open.

How could this be?

i replace that burnt plug. Tested it for spark on the block and it seemed to have good spark just idling. Even Arced out of the top of the boot to my hand. But it still is shuttering and shaking when I Rev up.

any ideas? Thank you in advance!

sincerely,
stranded in Georgia

 

Change the rest of the plugs. Do a compression test when the plugs are out. If compression is good and it still misses, change the coils.

 

Unplug the clip from the coil pack. Remove the 1 mountain screw. Mine is 11/32 hex head I think. Pull out coil pack. Plug is directly under the coil pack and should be a 5/8 plug socket. Don't use a standard socket because it won't lock into the plugs post and you won't enjoy fishing the plug out. Lol. Replace the plug making sure your gap is .054 then replace the coil pack plug it in and done

 

Coils shouldn't have much resistance measured with an ohm meter.
If the plug tip is melting like you say, I would suspect a lean mixture. Check the fuel trims and maybe replace the o-ring on the fuel injector.