Misfire
 

My dad has a '99 F-350 V-10 that is missing under a load. I have a scan tool and the truck shows no misfire code, and the data stream shows that it has misfired, but does not break it down to individual cylinders. We think it might be a bad coil boot, but is there any way to determine which it is without checking all of them? Thanks

If it is struggling during the miss it might be more than one coil causing the problem. But it could be that the timing set is worn out and causing the timing to be off a little.

I too just had a COP go bad on my 2001 V10. Luckily a code was set and it ID'd the cylinder. Your truck must not have a dead hole (no spark in one cylinder) yet so the on board diagnostics aren't able to tell you which cyl is the culprit (in '99 the OBD wasn't that good for over 8,500 gvw trucks like yours). You may be able to access individual cylinder misfire counters with a good scan tool (Snap On, SPX, Ford IDS) but I'm not sure if it was even support for your powertrain. If it is only missing under load it would be pretty tough to find which one is the problem. You can buy one new COP and keep swapping it and taking the truck for a drive until the problem goes away. It'll take a while but you'll eventually find it. Might me a good time to change the plugs too.

Thanks. We changed all the coil boots and all the plugs, but it still misses occasionally. We checked the resistance in all the coils and they all checked good. We have had it on a snap-on scanner and it shows nothing too. I guess when it gets bad enough we will find it.

I still wouldn't rule out a coil going bad. Usually an ignition related misfire will start by a coil failing under heaver loads. I resistance can still check out fine but the coil can still be breaking up under higher temps/loads. Also, it may not be ignition related. How many miles are on it?

I didn't catch this thread before you changed out you old boots.
Ford will usually diagnose something like this with a water bottle filled with some water and vinegar mix. Spray around the cops and boots, run it a little and then check for the codes again. These v-10 won't throw a code when things are intermittin, only when they go south.