Coleman UT400 won't rev. Idles fine

[Will Sutton]

I've got a 2023 UT400 (bought from tractor supply) and I've been beating my head against a wall with it.

It will start and idle perfectly. The second I touch the throttle it sputters and dies.

I've checked that the fuel pump is working  (it is).

I've replaced the injector, throttle position sensor, O2 sensor, and intake air sensor. All with no change.

 

I've just taken a look a the schematic, and there is a crank position sensor as well.

Could this be the source of my troubles? If so, where is this thing located? I can't seem to find it on any drawings from the parts suppliers.

[Will Sutton]

Update:

I purchased a new crank position sensor (and stator) and installed them.

No change.

While I had everything apart, I checked the timing.

The AC magneto cover has two "|" marks, one lines up with the cam position indicator (and dot on the gear).

This seems to also align with TDC of the piston.

At this point, I'm beginning to suspect the ECU.

[TexasBuckeye]

I don't have the 400, I have a 550.  I am assuming it probably has the same interlocks, but is it possible you don't have your driver side seatbelt latched or that the contact is not changing state when you do?  The wiring can be accessed in the engine compartment right behind the driver seat where there is a cable connection and you can check it (you are checking the cable from the seatbelt).  The contact is closed when the seatbelt is not latched, and the contact is open the seatbelt is latched.  You can disconnect the cable (bypassing the interlock) to see if that makes a difference. 

[Will Sutton]

I thought that too. But the wiring has been bypassed and the seatbelt connected for good measure. 
 

Before I did that mod, it would rev easily to 4k and then just pull spark and fuel to keep the 4k limit. Now anything beyond idle results in this behavior. 

[Tricky]

I think we are in the same boat. I have not replaced all the components you have I have been attempting to trouble shoot it with the computer. So far all systems look good but I still have the same issue. I pulled the plug again and it looks fine. In the past a fresh fuel filter would make things improve. But that has not been the case this time. I hope you figure it out and if you do please let us know your findings.

[Will Sutton]

I was actually about to update. I got a replacement computer off eBay (Coleman of course said I was out of warranty). That got it back to drivability.

It seems to be running a bit lean, and wont idle. I’ll swap the old injector back at some point, maybe swap to 87 octane. 
 

I’ve got an older mower that doesn’t like premium but runs like a champ on the cheap stuff.

I cant imagine this thing has two modes “Can’t rev” and “Won’t idle “

[Tricky]

I truly dislike the way we are almost forced to do troubleshooting by parts swapping these days. However, I was thinking of getting a new computer as well. I am sure amazon sells them but as with as with all things it can be a bit iffy. I will check eBay as well. It would sure be nice if TS had planned ahead and made sure there were qualified repair shops before they began selling these. Have you tried the PC software HUD ECU HACKER DOWNLOAD ?I followed the excellent instructions from aefron88 and was able to view the codes. Honestly I am not able to make heads or tails of it other than to see that everything appears to be working fine as best as I can tell. It goes without saying I need to buy a manual for it rather than guessing if things are within tolerances. I have two of these UTV's mine is not usable and my wife's is beginning to have problems which is beginning to elevate the priority level of figuring these things out  On mine I adjusted the valves replaced the spark plug, several new fuel filters, cleaned the air filter, cleaned the O2 sensor and MAF. I replaced my plug wire as well. I then did the ECU reset procedure. I saw where some one had theirs jump timing and and now needs a new motor. I think I will find the timing chain tensioner procedure next and while there check compression. Gone are the days of slapping a new carburetor on news points plug and condenser and calling it good. 

Things are finally cooling off in Florida so I guess it will soon be time to stick it back in the shop and really dig in to this thing. If I find the magic cure I will post the results and try my best to sound like I know what I am doing LOL

[Joe Breaux]

I feel your pain...wish I had a solution

[Will Sutton]

19 hours ago, Tricky said:

Have you tried the PC software HUD ECU HACKER DOWNLOAD ?

I have actually tried that. The original computer exposed so few sensors that its nearly worthless. That was with a J2534 adapter, I didn't try the K-line ones.

I halfway want to get a tunable MT05 and make my own spark/fuel/timing tables for it, because we can't download the ones from the OEM (though I might try).

There is a service manual on this site. As far as checking timing, its not terrible, but best done with the fuel tank removed.

A more modern ECU would be able to debug sensors better. This one is closer to an early 90s computer at best.