My 2005 class C is built on a 2004 frame with the Ford V10 in it. It has developed an intermittent misfire this year but not enough to give a CEL. Google searches tells me that it probably needs new plugs to cure this.I am planning to replace the plugs despite their low mileage although being original. Rig only has 26,000 miles on it. Should I do coils at the same time or just the plugs?

I'm not a fan of replacing parts in hope it will cure the ailment. Sometimes we need to, but I'd dig deeper and find root cause. It may not throw a code, but reading data while driving (having co-pilot to help) would be better. Could be a long list of things from plugs, coil pack, and more. Having had a V10 in a C, I've not experienced the misfire issue. Hopefully you can gather more info, perform a few tests first.**real life example: my friend had intermittent issue with a zero turn not starting, not even turning over. He began replacing parts...battery (twice), starter, coil, some other items...turns out, after all that, he mentions it to me...and after 30 seconds of looking at it, I saw a loose ground to frame. That did it. Not saying yours is that easy...but in this case, $500+ spent and turns out issue was to put the proper lockwasher on the ground to keep it tight.Issues such as random misfire can be hard to diagnose.

More likely it’s the coil pak rather then the spark plugs. If you put a code reader on it it will tell you how many misfires there are on each cylinder. I’ll bet one or two of them has an exceptionally high number of misfires compared to the others.

nickthehunter wrote:More likely it’s the coil pak rather then the spark plugs. If you put a code reader on it it will tell you how many misfires there are on each cylinder. I’ll bet one or two of them has an exceptionally high number of misfires compared to the others.^^^^^^^THIS^^^^^^Get a OBDII code reader, they're cheap. Over 100k miles on my 2002 and still has original plugs. However I have replaced 3 coil packs in that time. Code reader tells me which cylinders are misfiring.

^What these guys said. Likely one or more of the coils. Very common Triton motor issue, all displacements. I’d narrow that down, replace the one(indicated bad) figure out how to check that with code reader and keep a spare one or 2 for future quick fixes. However the bigger issue with the Triton platform is the spark plugs. And there were 2 different issues. Some will shear the threads in the head and spit out plugs (also easy to strip or shear threads off when removing them, especially now that they’re old and corroded, anything with original crusty plugs is more likely). Other models the plugs will rust in and stick and the plugs will snap off and stay stuck in the head. I believe your model year and V10 is a spitter, not a sticker. And being 2004 is a 3 valve motor which has 8 threads vs the original 2 valve heads which had only 4 threads. Regardless, both engines will spit plugs, the 2V is more likely than the 3V. And some would also randomly loosen due to mis matched mating surfaces. And others would break the spark plug (8 thread heads) resulting in a similar condition to the ones that even more commonly got stuck but not as often. I’ve had 2V V10s spit plugs and newer v8 tritons stick plugs. Never had an issue with the 3V V10s and had a few of those too. Adjectivally they are IMO the least bad of 3-4 different bad designs. Few years ago bought a pristine 30k mile Mustang GT (a sticker not a spitter). Car never even saw rain in over 10 years until we bought it. I went after the plugs right away and it was touch and go getting over half of them out without snapping them. If I was planning on keeping it a lot longer, I’d first verify and fix the issue with the misfires which is 90% chance the coil packs. Then I’d analyze whether to get those plugs out of there or not. And I’d buy repair kit (it common enough that there are diy repair kits available forever now) and know how to use it. And use copper antiseize on ANY/ALL Triton spark plug threads. For different reasons based on what engine it is. Also good news if it does spit one plug, it’ll still run well enough to get you somewhere besides the shoulder of the road, but with the obvious consideration of it pumping out gasoline vapor 2-4000 times per minute…lol. Not sure I’ve ever seen random misfires as a defective spark plug condition in hundreds of 2 and 4 stroke engines. Fix the coils and then if you win big at the casino one night, your luck may be still good enough the next morning to get the plugs out without stripping or breaking any.

Idk how bad the access is on a C van chassis to repair stripped blown out threads. Only did it once on an old 2V class A but removing the doghouse provided good access.

2005 E450 Ford V10 intermittent misfires | Good Sam Community

opnspaces
Navigator II
Aug 24, 2023
Sometimes you just gotta bite the bullet. But at least it's fixed. Now on to life's other adventures.
Valpo_Camper
Explorer
Aug 24, 2023
Well I can do quite a bit under the hood of a car but this job kicked my butt and humbled me to applying the credit card wrench to it. 3 different cylinders were misfiring plus random misfire code is what the shop came up with. Replaced all 10 plugs and coils and did a fuel system cleaning. Runs like a big heavy smooth box again.
Krusty
Nomad II
Aug 21, 2023
katleman wrote:
bobndot wrote:
CEL can light-up due to a bad or dirty electrical connection from the ECU to the sensor.

My mechanic always checked that at my service intervals.

And specifically throw only cylinder misfire codes (P0300 & P030X), no other codes?

We’re talking once a mile or so.

Check and make sure the center bolt holding your harmonic balancer on has not come loose
katleman
Explorer
Aug 21, 2023
bobndot wrote:
CEL can light-up due to a bad or dirty electrical connection from the ECU to the sensor.

My mechanic always checked that at my service intervals.

And specifically throw only cylinder misfire codes (P0300 & P030X), no other codes?

We’re talking once a mile or so.
bobndot
Explorer II
Aug 21, 2023
CEL can light-up due to a bad or dirty electrical connection from the ECU to the sensor.

My mechanic always checked that at my service intervals.
Grit_dog
Navigator
Aug 21, 2023
^Very frustrating when competent diagnosis fails. Good news is it runs just fine I suppose.
Your rig is new enough that chaffed wires, corrosion etc are lower on the list of possible causes, but if there’s any areas on the injector, coils and or main ECM harness you haven’t checked, including unplugging all harnesses and just looking for visual damage to the pins or connections, that’s where I’d likely go next.
And it’s not out of line that you may have picked up a furry traveler along the way who likes multicolored licorice (wire insulation) or spent a night or 2 in pack rat country and they snacked on some wires.
If you have camped where it looks like everyone is working on their engines (hoods up), they’re not. You’re in packrat country. And those things are pure evil to vehicles and other things.
katleman
Explorer
Aug 21, 2023
zigzagrv wrote:
Did you check your battery voltage? Had a similar situation once where after I would stop for a short while and when restarted, it would run rough and throw codes till I got up to speed. Turned out battery was bad and till the alternator built up voltage, this would happen. New battery solved the problem.

Battery is new this season, replaced proactively, not out of need.

The codes are thrown at idle, up hills, down hills, doesn’t appear to vary with load.
zigzagrv
Explorer
Aug 21, 2023
Did you check your battery voltage? Had a similar situation once where after I would stop for a short while and when restarted, it would run rough and throw codes till I got up to speed. Turned out battery was bad and till the alternator built up voltage, this would happen. New battery solved the problem.
katleman
Explorer
Aug 21, 2023
Been up in Alaska all summer, my 2016 E450 Ford V10 (26,000 miles) has had the CEL on for the past five weeks. According to my OBD2 scanner, it first started throwing P0300 (generic misfire), then it claimed cylinder 2 was the culprit (P0302)

Replaced the air filter as it was filthy. Nope.

At the point its flagging 4 different cylinders, split between the two sides, had a mechanic diagnose it, suggested bad fuel or water. Tossed in SeaFoam and iso Heat. Nope

Refusing to believe it’s the plugs/coils on 4 cylinders, as they are good for 100k miles, tried replacing the MAF sensor. Nope.

Bit the bullet and replaced all the plugs and coils. Nope.

All through this period of misfires, which was flashing the CEL once a mile, no loss of power, no loss of fuel economy, drove just as it always has.

So I’m heading homeward with the CEL flashing, run out of things to check or replace. Stumped every mechanic I have consulted.
way2roll
Navigator II
Aug 13, 2023
Valpo Camper wrote:
Well the saga continues on this and my scanner.

Went and scanned the RV and my scanner will not give me misfire data on the Ford engine. WTH??? Updated software on the scanner and will go back and test again. If all else fails I will try the cowl off in the dark to check. I do not hear a tick but we shall see what gives.

Not sure when your plugs coils and wires were replaced last but it may very well solve your problem even without diagnosing a particular cylinder. AS one coil fails it stresses the rest and in turn they can also misfire. Just replace the coils and plugs and go from there. They probably need replacing anyway. Willing to bet it solves your issue.