1999 Super Duty 6.8 v10 missing and running rough...
 

I have a 1999 f250 6.8 V10. I purchased the vehicle with a motor having been installed at the dealership 10000 miles ago.It has a 36000 mi warranty. It started missing the other day so I took it in and they told me to start at the #5 Coil and plug. Did that. Still running rough. It has good power when you gun it and then when you let off and just give it a little gas it shakes badly.It will only get to about 60 on the speedo and sounds really bad. Should I just keep replacing coils and plugs until I get lucky.Dont want to really let dealership do that and they charge 100 every time just to tell me what may be wrong with it.

What you can try is to buy a few new ones and replace one at a time until you find the next coil that is bad. It is easy to do. or what I did when I had a similar issue with mine a few months back and I just replaced all the boots($7 a piece) and it fixed my problem. I had a few that were rusty and cracked on the passenger side near the firewall end.

My truck started missing last weekend and I had a hell of a time finding it, it was not showing any codes. I could barely hear the miss at idle but what I did was let the truck idle and unhook and rehook each coil 1 at a time and the one that does not change the sound of the engine is your problem. Mine was a cheap fix it was the boot, if you find the bad cylinder pull the boot out and look for any little white marks on it (like mine had) that is ware the spark is jumping through the boot and causing the miss. (just watch the fan don't ware loose clothing) GOOD LUCK!!:-wink

I think I'm gunna have all the plugs and wires/boots changed and a new fuel filter. It needs a tune up anyway, Im just worried about them not torquing the plugs right and poping one. Anyone know what the torque is for the plugs????

Go to the V10 section and there is a ton of info there in the tech folder at the top of the page.

Here is what you want Post #4 https://www.ford-trucks.com/forums/8...ch-folder.html.

Isn't it within the warranty? shouldn't they do this for free?

Thread moved to Modular 6.8 Forum.

Don't overlook the vehicle speed sensor mounted on the rear pumpkin. When those go bad, it can cause all kinds of issues while driving.

If you are getting a CEL, you need to get it scanned and see what the computer is saying is wrong. It may just show a different cylinder is misfiring.

OK. So I guess that you did the "unplug coils thing" and found that number four made a difference in the sound and then replaced it. Then the truck ran great. Sweet! Then it ran crappy again? Not Sweet. Maybe it is another coil. I agree with Mikes... and think you need to get the codes read and reset them, not disconnect the battery. I know that here in Cali there is aamco that reads codes for free and many of the oil change places do also. Get the codes and this site is great at helping!!! :-X25:-X25

Unfortunately I just don't have time to look at it myself right now so I took it in to the shop. They called and said its a coil on #4 so I had them order it. We'll see how it runs tomorrow.