Will Sutton

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.

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 “

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.

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.

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.