RZT-SX 50 Engine Run Problems

[jleblanc]

Hi there,

I'm looking for some advice / guidance on troubleshooting my mower. I'm also wondering if my issues are common with other similar mowers.

I have a 2020 RZT-SX 50 with an EFI Cub Cadet engine, model #17AWCBYZ596. It has frequent issues with starting when the engine is cold. When this occurs, the engine also has trouble staying running for the first 5 or so minutes. It feels like a carbureted engine with poor tuning, improper choke setting or fuel starvation. This is a fuel injected model with no individual choke control. When the engine is difficult to start, it will often stall with no warning even after an hour of use. When it stalls like this, it is often very difficult to restart.

Other times, the engine fires right up without issues and works perfectly.

The digital display has never shown any codes. The machine currently has 39 hours and has had these issues since I bought it last year with 27 hours. I initially assumed it had old gas since it would eventually run, but new gas and fuel system cleaner hasn't corrected the problems. The engine also always cranks over, just sometimes doesn't fire up or stalls immediately after firing up.

I've checked the basics like looking for a clogged air filter, clogged gas tank vent, clogged fuel strainer, loose fuel line hose connections, sticky throttle & governor linkages, fouled spark plugs, poor grounds, loose connections but all of those where found to be in good order.

Another issue that may or may not be connected is that the headlight inconsistently strobes when the engine is running. When the engine is off, the headlight stays continuously lit as it should. I've removed the headlight and tested it using a 12V battery and it worked fine. While I was at it, I checked the continuity of the harness and it was also fine. Just to make sure it wasn't a loose connection, I ensured the connections were greased and tight but this didn't fix the issue either.

Any help on resolving this would be greatly appreciated.

[jleblanc]

Update: The engine won't start.

I continued to use the mower with intermittent starting and stalling issues since I couldn't figure out the issue and needed to mow my lawn.

One day it stalled and now the engine won't crank over. When I press the plastic red key on the push button start ignition module, there's only a faint pulsing/clicking sound coming from the ignition module. No other noises anywhere else and nothing displayed on the ignition module's digital display screen.

So far all these have tested well. Battery, seat switch, PTO switch, EFI relay (tapped below the ignition module), 20A main fuse, all the grounds I could find and confirmed the magnet is still functioning on the plastic red key. Visual inspection of the ignition module's PCB didn't find anything wrong and its relays tested good.

I've also confirmed 12V power going to the correct places, according to the electrical schematic, when the ignition is off. These being the ignition module (one wire on each connector), starter solenoid's hot lead, engine's main 6-pin connector and EFI relay.

Tomorrow I have some time to look at this again and I'm planning to test the parking brake and reverse switches again. They tested good before it completely died but I'll test them again just in case. I'll also keep checking for continuity along each of the safety switch wires.

This now seems like a safety switch communication issue with the ignition module but I'm still not sure. Anyone else experience this issue and/or have any troubleshooting suggestions?

[jleblanc]

Here's a copy of the electrical schematic that the service advisor at my local dealer provided.

c06f83ef-5eec-46d4-bcfe-5c9a22120fe5.jpg

[jleblanc]

I got the mower working again! But I wasn't able to figure out exactly what was the issue, so I hope it last.

Long story short, I think it was an issue with the wiring harness. Most likely a pin in one of the connectors not making good contact.

In case this helps anyone in the future, here's what I did to get the machine cutting grass again.

To recap, the push button start (PBS) module's display wouldn't display anything. When pressing the key, the engine wouldn't crank over and only a faint pulsing clicking sound could be heard from the PBS module. Maybe from the relays on its PCB?

To troubleshoot, I first tested the battery and that was good. Then the 20A main fuse which was also okay. I then back probed the two power feed wires on the PBS module and they showed the same voltage as the battery, so it was confirmed that the module was receiving power.

I then tested the voltage on the PBS module wires which should be receiving power once the key is pressed. This showed the voltage dropping from 12ish volts to as low as 6ish volts when the start button was pressed. I'm not sure if this is normal but I suspect that it is not.

Assuming a short or a frayed or partial broken wire, I started looking for one. I ended up testing nearly every wiring circuit for continuity and resistance along with every switch, but I couldn't find an issue. Just to be 100% sure there wasn't a frayed or partially broken wire on the power feed to the PBS module, I tested each power feed wire and these circuits' ground wires with a 12 volt incandescent light bulb. Each wire was able to able to light up the bulb nice and bright so they were all in good condition. I also visually inspected every wiring connector but didn't find an issue.

Not finding an issue and not knowing what else to do, I put all of the wiring back together and tried starting the mower. Without any hesitation, the engine fired right up! I was shocked but relieved. I then reassembled the mower fully and tried re-starting the engine. Again, it started right up without issue so I must have fixed something.

Since it's been working again, I've put another 3 hours on the mower and it's worked like a champ. All I can think of is that a pin in one of the connectors wasn't making a good contact. I'm leaning towards the output wire of the 20A main fuse, but who knows for sure? Either way, it's cutting grass again!