Coleman 400 fouling plug

[Bobby Courtney]

I have a 2021 Coleman 400utv with 60 miles on it. I bought as project. It’s idled ruff and fouled plugs since it was new. I have removed and cleaned throttle body new injector new idle air valve new oxygen sensor. Installed ngk iridium plug. Starts and run good for about 5 or 6 miles and fouls plug. It runs rich all the time. I’ve done reset on ecu. I’m about to think it’s time to try a new ecu. Anyone please help. 

[Rainman]

11 hours ago, Bobby Courtney said:

I have a 2021 Coleman 400utv with 60 miles on it. I bought as project. It’s idled ruff and fouled plugs since it was new. I have removed and cleaned throttle body new injector new idle air valve new oxygen sensor. Installed ngk iridium plug. Starts and run good for about 5 or 6 miles and fouls plug. It runs rich all the time. I’ve done reset on ecu. I’m about to think it’s time to try a new ecu. Anyone please help. 

I had a similar problem. With mine, which has under 30 miles and under 20 hours on it, It was hard to start, ran rough, and until it was warmed up, if I gave it gas I would hear a pop and it would stall. The plug was carbon fouled, as well as the oxygen sensor and the tailpipe was loaded with carbon buildup. Cleaned it all up and did the same thing with replacing the spark plug and the problem came back within an hour or two.

Took it to my mechanic and after four days he said the gas tank had lots of water in it and that was the problem. He cleaned the tank, put fresh gas in it and so far, it's running like a champ.

Hope this helps ...

[that guy from Canada]

^^^^ check that first ^^^^

I would almost consider a new coil and the often overlooked spark plug cap.

Also as a 4 stroke it wont hurt it to try one hotter heat range plug.

Ex: dpr7ea use dpr6ea lower number is hotter

[Rainman]

28 minutes ago, that guy from Canada said:

^^^^ check that first ^^^^

I would almost consider a new coil and the often overlooked spark plug cap.

Also as a 4 stroke it wont hurt it to try one hotter heat range plug.

Ex: dpr7ea use dpr6ea lower number is hotter

Interesting ... as I am not too familiar with UTVs, which is part of my problem in trying to fix anything with it, and I didn't know they had a spark plug cap (unless I'm thinking of a distributor cap) and wasn't even thinking of the coil. I have the same year and model as you (2021 UTV 400) and have found limited information on doing repairs.

I'm old school and grew up working on vehicles with spark plugs, spark plug wires, distributor cap, points, rotors, carburetor, etc. Now with my 2019 truck, whereas everything under the hood is electronic and covered with plastic covers, I'm totally lost.

Looking at the UTV, for me, it's a totally new animal and I can't figure which way is up with this thing, but I'm relearning as I go along.

Going back to old school, carbon fouling is usually a symptom of a fuel problem. If you have verified no water in the gas, then it could be fuel/air mixture, but you should have injectors, and the fuel/air mixture I believe is controlled by the ECU and you reset that. Try checking your air filter to make sure it's clean and installed properly. I remember reading some place that these rigs came out of the factory, in many instances, with the air filters installed backwards, which had caused some problems. Also check your idle speed to make sure it's not idling too low, although I think it would take a while to foul the plug with a low idle.

If I think of anything else I will surely forward it to you ...

[that guy from Canada]

Your thought process is correct im just always simple first.

the spark plug cap on the plug has a built in resistor that can fail, system is..  coil, coil wire, cap, plug.

unless it us coil on plug 1 piece unit that goes straight on plug.

Either way if you have weak spark you will foul plugs.

2 stroke never run hotter plug to prevent fouling, engine damage will result. 4 stroke 1 range hotter wont hurt the motor. You could simply try that.

[Joe Breaux]

if its just a rich fuel problem, and fouling plug in 5 minutes, you should see black smoke and the exhaust should burn your eyes. Did you try just changing the plug or wire ?   Is it dry black carbon fouled or wet fouled ? 

[Bobby Courtney]

18 hours ago, Joe Breaux said:

if its just a rich fuel problem, and fouling plug in 5 minutes, you should see black smoke and the exhaust should burn your eyes. Did you try just changing the plug or wire ?   Is it dry black carbon fouled or wet fouled ? 

Dry black carbon. Before I changed all the parts it was black wet with gas carbon. So I’m making it better just running out of options now. 

[amiracle40995]

I have a 2019 Coleman 550. I haven’t went over 100 miles before I fouled a plug. I started using 93 octane and I added some grounds to the electrical system. It idles a little better but I buy plugs3 at a time.

[that guy from Canada]

Look up in thread, try one hotter heat range plug than stock.

Ex: cr7hsa use cr6hsa NGK

Lower number is hotter