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New member, this is my first post here.



I bought a Cub Cadet XT3 GSX with a 60" fabricated deck last autumn, which I like a lot, except for the fact the Kohler CH740 rarely runs smoothly through a whole mowing. It's done this since new - I'd take it back to the dealer, but they're five hours away (I bought one of the last XT3s I could find anywhere, as they're discontinued now, and had to drive that far to retrieve it). We have a True Value store about a half-hour away that carries Cub Cadet, and I'll take it there if I can't troubleshoot on my own (with hopefully some help here!).

The engine will run smoothly for a while (maybe 30 minutes, although sometimes the symptoms start immediately, even from cold), but then it acts like either A) it's starved momentarily for fuel, or B) the ignition got switched off momentarily. Once this begins happening, it will progressively get worse until the engine dies.

I'm led to believe it's an electrical problem because it won't start about half the time once it dies completely (by that, I mean turning the key to the start position results in dead silence - no click, etc.). Letting it sit until cool usually means I can start it, but not always - I sometimes have to keep worrying it until it will eventually start. After I get it starting, it will continue to start okay again until it dies out as before.

The first time it happened was while mulching leaves in the autumn right after I bought it, which caked up the air filters pretty bad. Cleaning the filters seemed to help at the time, but with the new mowing season ramping up, it's got a fresh, clean filter in place (as well as fresh oil/filter since I'm past the break-in period). I briefly removed the air filter to see if that made any difference, which it didn't. Also briefly unscrewed the fuel fill cap, in case it had a plugged vent, but again with no difference.

My engine model is CH740-3328 and the s/n is 5127807843. It has about 18 hours on it.

I have the PDF service manual as well, and read all the threads here with CH740 mentioned in them. The ignition kill circuit seems like something that may be suspect, or possibly the key switch. But on a brand-new machine?

Any suggestions welcome!

Ed

With it being that knew i would suggest take it back to the dealer and let them figure it out under warranty. There may be a history of CC having issues on that mower with that engine that may not be engine related.

Check the battery leads, both of them at both ends

All connections I have access to seem to be tight. It cranked up this morning, but started acting up within a few minutes, then died with the no start condition again. I stopped at the True Value in town and they said they can take a look, but they’re backed up at least a week - the main reason I dislike taking anything in for service. I mowed last night (it died just as I finished and it sat in the yard overnight), so now’s the best time, I guess!

es

It’s at the dealer now, will report back what they find.

es

Back from the dealer, $70 lighter with no resolution.

As noted earlier, it had died after my last mowing, and while it cranked the next morning, it immediately started cutting out and then died again (no click or any noise when attempting to start). Wife and I tried to push it up the ramps on the trailer after me trying to start it multiple times; we couldn't get it all the way up the ramps, and wife said "try it one more time," after which it cranked up and ran fine. Perhaps we jiggled something in the process of pushing it up the ramps?? Who knows…

At any rate, the mechanic ran it 1.5 hours and it never hiccuped. Of course, I'm sure that means he cranked it up and let it sit, rather than actually driving it around with the mower running, simulating conditions under which it failed in the past. He apparently replaced two 20¢ connectors and said he went through all the grounds to make sure they were clean and tight. But since it did not exhibit any problems in their shop, it didn't fall under a warranty repair. The mech also wanted to argue that I should only use non-ethanol fuel (I've used stabilized pump gas for 30 years in all my small engines with no issues), and the owner then tried to blame the problem on my electric sleeve hitch, despite the problem having existed from new, before I added any accessories; not to mention the sleeve hitch uses the same type electric lift as that used on the factory deck.

Some of you older folks may remember the Model Garage series that ran in Popular Science Monthly from the late 1920s through 1970. One of Gus Wilson's repeated mantras was to find out what the actual problem was - especially if it appeared to be fixed for no apparent reason. That's where I feel I am with this shop.

I'll be mowing after lunch and we'll see what happens then.

es

stembridge said:

I'll be mowing after lunch and we'll see what happens then.

es

Click to expand...

Ran perfectly the whole time I mowed, so there's hope!

es

IT can be very frustrating
I have run mowers for hours on end on the farm where my workshop is so the mower was working hard in mixed pasture grass and they never miss a beat , then when I go to unload them at the customers residence they play up , or they work perfectly for a coule of mows then the problem returns .

Ran it another hour or so yesterday, moving mulch with the Johnny Bucket. It hiccuped once, while I had it idled down, but ran strong the whole rest of the time.

es

Mowed today with no problems, then put another hour or so on the tractor moving manure with the bucket to fertilize some bare spots in the yard - again, no problems. Hope is growing that it might actually be fixed!



es

One (hopefully final) update that I've mowed a couple more times as well as run the tractor several times for ~30 minutes or longer for other uses with no problems. Seems like it's fixed.

es

UPDATE

After mowing all summer with no issues, the same problem has cropped back up. The first time was while I was mowing recently, and I noticed a LOW BATT message on the LCD as the engine started to sputter. Barely made it back up to the shop before it died. Battery was at around 12.3V. Putting it on a 4 amp charger for a while brought it back up, and it started okay at that point.



Took it to a tractor show along with my 8N, and it died again while driving it down to enter in the slow race, and would not start (not turning over, not even a click from the starter solenoid). Battery was at 12.4V on the LCD screen. Let it sit a couple hours and it started up, which allowed me to get it loaded on the trailer. Would not start when I got home, however. Put it on the charger a bit and it started, so I unloaded and left it in the shop.

Put it on the charger overnight, and when I checked the next morning, it was back to "no start" condition (no click, not turning over), but other electrical equipment worked fine (lights, deck motor, etc.). Battery indicated 12.8V, engine off.

I pulled the engine-to-body wiring harness connector apart and cleaned those contacts up (there was a bit of white 'haze' on them), and put a squirt of OxGard on the pins. The Kohler CH740 service manual has a test that says to depin the white wire from this connector (safety switch ground) and attempt to start to determine if a safety switch is the issue. Tractor started right up, so I reinstalled that wire in the connector and the tractor started again without issue.

I mowed the grass later in the day and the tractor ran fine the whole time.

After I was done mowing, I let it cool down, then ran the tests in the service manual for the voltage regulator/rectifier, to see if I have an insufficient charging issue due to observation of the battery voltage repeatedly getting low. I initially couldn't even find the rectifier (!), but after searching pictures of the CH740 online, saw that it's mounted on the side, down low at the flywheel end of the engine. As installed in the XT3, it's located on the engine such that it's mostly hidden by the tractor frame, and I ended up removing the black plastic filler panel below the rear of the hood (left side, facing forward) to gain better access. All tests passed without issue, but the connector itself had a lot of crud in it, so I scraped it out as best I could and put a shot of Oxgard into each pin, then put it back together.

After sitting overnight, the battery was reading 12.6V, but it started and ran fine so I moved it back into the garden shed. After shutdown, the battery read 13.4V on the readout, but was dropping - same thing I saw with it in the shop. Don't know if that's a clue or not, but thought I'd include it.

Appreciate any suggestions based on the info provided.

es

Sounds like a duff rectifier / regulator
Note there are 4 electrical connections for the rectifier, the 3 pins + the body ( ground )
Kohler like to use a brass strip in the blower housing to do this which is prone to work hardening and cracking .
The simple test for a duff rectifier is to run the mower so the battery is fully charged then remove the rectifier plug
If that stops the battery drain or slows it down drastically the rectifier or stator is duff
Fully charge the battery on an external charger then take voltage readings every few hours
Strait off the charger it should read 13 V to 14 V ( over voltage is needed for charging ) which should drop down to around 21.6 V ( a lead acid cell is 2.1 V ) and stay there
IF it drops down to 12 V or less over 5 days the battery is duff & self discharging .

It will be at least 4-5 days before I mow again (we need rain!), so I'll keep an eye on it. What you described matches what I'm seeing - battery is at ~13.8V immediately after shutdown, then drops to around 12.6-12.8V over the next minute or so. The last couple times it died (after I realized the LCD shows battery V for a couple seconds on start sequence), it's been as low as 12.3V, which seems to be around the point the LO BATT message is triggered.

I did check the rectifier-to-ground wire as well (measured between rectifier body and engine block) - no issue there.

es

stembridge said:

I did check the rectifier-to-ground wire as well (measured between rectifier body and engine block) - no issue there.

es

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Curious, what did you check between the regulator body and engine block? Thanks.

VegetiveSteam said:

Curious, what did you check between the regulator body and engine block? Thanks.

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Ohms, read 0 or maybe 0.001 or something like that.

es

What do you have at the battery with the engine running full speed? It should be between 13.8 and 14.7 VDC. If you have that, then the charging system is working correctly.

If lower than 13.8 turn the engine off and then turn the key back to the on position. Unless you have a 20 amp charging system or greater the B+ wire at the center terminal normally runs through the key switch so with the key off there is no connection to the battery. With the black lead of your voltmeter connected to the negative terminal of the battery, touch the red lead to that center violet colored wire in the regulator plug for DC volts. It should read within a couple of tenths of what you read at the battery. If you have good battery voltage there, reconnect the connector to the regulator if you've disconnected it. Now with the black lead of your voltmeter still attached to the negative terminal of the battery and the key switch still in the on position, touch the red lead to the metal case of the regulator. If you read battery voltage, the regulator isn't grounded. Simply fix the ground.

The last thing to check, again this is if the voltage at the battery is below 13.8 at the battery while running is the stator output. With the engine running at full throttle, turn your voltmeter to AC volts. Now go to the regulator where the spade terminals meet the connector. Touch the leads of your meter to the spade terminals the white wires connect to and take an AC voltage reading. It should read more than 28 VAC. There is no maximum so it could read 40 plus VAC but it needs to be 28 or above. Typically they read in the mid to high 30s.

Hope this helps.

VegetiveSteam said:

What do you have at the battery with the engine running full speed? It should be between 13.8 and 14.7 VDC. If you have that, then the charging system is working correctly.

If lower than 13.8 turn the engine off and then turn the key back to the on position. Unless you have a 20 amp charging system or greater the B+ wire at the center terminal normally runs through the key switch so with the key off there is no connection to the battery. With the black lead of your voltmeter connected to the negative terminal of the battery, touch the red lead to that center violet colored wire in the regulator plug for DC volts. It should read within a couple of tenths of what you read at the battery. If you have good battery voltage there, reconnect the connector to the regulator if you've disconnected it. Now with the black lead of your voltmeter still attached to the negative terminal of the battery and the key switch still in the on position, touch the red lead to the metal case of the regulator. If you read battery voltage, the regulator isn't grounded. Simply fix the ground.

The last thing to check, again this is if the voltage at the battery is below 13.8 at the battery while running is the stator output. With the engine running at full throttle, turn your voltmeter to AC volts. Now go to the regulator where the spade terminals meet the connector. Touch the leads of your meter to the spade terminals the white wires connect to and take an AC voltage reading. It should read more than 28 VAC. There is no maximum so it could read 40 plus VAC but it needs to be 28 or above. Typically they read in the mid to high 30s.

Hope this helps.

Click to expand...

Going from memory here, but engine running voltage was 13.8 or 13.9. I'm pretty sure DC volts at the regulator plug were 0.1 difference from battery voltage. I'll have to do the regulator ground test you suggest for an answer there - all I looked for was a good ground from the regulator body to the engine block. AC voltage off the stator was ~40V.

Appreciate the suggested procedures to run!

es

If you’re getting 13.8 or better at the battery, the regulator is grounded. Sounds like the charging system is fine.

Used the XT3 to pull my yard wagon yesterday (starting to clean out the garden), and it fired off fine. Battery was indicating 12.5V before I started it (after sitting for five days). I let it run at full throttle while I was working (maybe 45 minutes), and it hiccuped once or twice toward the end of that time. We'll see how it does when I mow again (and put it under load), which may be a few more days due to it still being dry.

es

UPDATE: Mowed yesterday and not a single hiccup. Hopefully I've found the issue, but I won't be 100% convinced until it goes for several months without the problem recurring.

es

I've run the tractor a couple more times, the last was plowing up my garden spot. As I started the first pass (putting the engine under load), it started spluttering again, so at the end of the row, I hopped off and jiggled both the engine-to-tractor harness connector as well as the rectifier connector (both of which I had squirted OxGard into previously). That seemed to do the trick, as it ran smooth the whole rest of the time I used it.

es

Well, it's back to sputtering again. Disconnected both connectors mentioned above, cleaned and reconnected, with no improvement this time.

es

Uploaded a short video taken while the engine was stumbling:


es

Remove the fuel line AT the carb or FI pump outlet. Drain into a glass jar. Look for water at the bottom. E-10 and water is a common thing. Like right now, 35 at night and 70 in the day, You get condensation in the bottom of the tank.

slomo said:

Remove the fuel line AT the carb or FI pump outlet. Drain into a glass jar. Look for water at the bottom. E-10 and water is a common thing. Like right now, 35 at night and 70 in the day, You get condensation in the bottom of the tank.

Click to expand...

Install a temporary “nurse” fuel tank and see if it starts and runs for longer than 15 minutes.

I’ll check the fuel, today hopefully, but keep in mind that this issue sometimes gets so bad that the engine dies and then will not turn over for a while (starter does not even click). Lights will come on and I can raise/lower the deck, so there’s power. That’s why I’m pretty sure this is an electrical issue, not fuel.

es

Just attempted to start it to pull it out of the garden shed - cranked and immediately started cutting in and out, then died completely after ~10-15 seconds of semi-running. Will not restart (no click at starter), although other powered features work (headlights, etc.). This is consistent with what it's been doing off-and-on. I can't see how these symptoms line up with a fuel issue (but I'll still draw a fuel sample to check for water). Sure seems like an electrical gremlin!

Battery was showing 11.9 volts on the LCD display before I initially cranked, which is low. Battery had a good bit of crud on it, which I cleaned off - it's on the charger right now, which may or may not (based on previous experience) get it turning over again. (EDIT - charging the battery made no change - starter still won't click or turn).

EDIT #2: Disconnected the fuel line and got a good flow of gas, no evidence of water:



es

I tested between the battery end of the ground (black) cable and a stud on the engine - zero resistance (well, 00.1), which should indicate the cable doesn't have an open in it (tested with cable end detached from battery). Also tested between the battery end of the red cable (while attached to battery so it was powered) to where it connects to the starter, and was getting full voltage there.

Cleaned (wire-brushed) the battery ends of the cables as well as the attachment bolts and nuts, and charged the battery up to 13.1 volts.

All fuses (in the fuse block behind the dash) are good.

Took the key switch out, disassembled and didn't see any signs of arcing - contacts looked clean. Reinstalled.

Earlier this year I had tested the stator output, and it passed all the tests in the Kohler manual - it's charging fine, or was at that particular point in time.

Lights and deck lift work fine, but still no start (no solenoid click, starter does not spin). I do hear a relay click when I turn the key to the "on" position, though...

I have the wiring schematic from the parts manual, but parts of it don't make sense to me (it's been 40+ years since I built any Heathkit projects). It seems to be incomplete. I'm also not sure which ignition system I have - I can post the model and serial number if needed to determine that.

I know I should start tracing circuits, but am unsure where to check next other than what's mentioned above.

Really appreciate y'all's suggestions...

es

stembridge said:

I tested between the battery end of the ground (black) cable and a stud on the engine - zero resistance (well, 00.1), which should indicate the cable doesn't have an open in it (tested with cable end detached from battery). Also tested between the battery end of the red cable (while attached to battery so it was powered) to where it connects to the starter, and was getting full voltage there.

Cleaned (wire-brushed) the battery ends of the cables as well as the attachment bolts and nuts, and charged the battery up to 13.1 volts.

All fuses (in the fuse block behind the dash) are good.

Took the key switch out, disassembled and didn't see any signs of arcing - contacts looked clean. Reinstalled.

Earlier this year I had tested the stator output, and it passed all the tests in the Kohler manual - it's charging fine, or was at that particular point in time.

Lights and deck lift work fine, but still no start (no solenoid click, starter does not spin). I do hear a relay click when I turn the key to the "on" position, though...

I have the wiring schematic from the parts manual, but parts of it don't make sense to me (it's been 40+ years since I built any Heathkit projects). It seems to be incomplete. I'm also not sure which ignition system I have - I can post the model and serial number if needed to determine that.

I know I should start tracing circuits, but am unsure where to check next other than what's mentioned above.

Really appreciate y'all's suggestions...

es

Click to expand...

So far you have done a thorough job diagnosing and eliminating possible problems. Have you load tested battery? When it dies, does it suddenly just quit, or slowly die?

I'll have to take the battery into town to have it load tested - all I have is a basic 'toaster' tester, which I think isn't meant for small batteries.

The symptoms are such that the engine starts stumbling off and on, usually after running for 15-30 minutes, but sometimes immediately after start, as is my current case. If it runs, it might not kill the engine during one mowing session, but over several sessions seems to get worse until it dies and won't restart (no click from solenoid, no starter rotation, lights and other electrics work, tho). It's not consistent in how and when it dies, at least I've not recognized any pattern yet. It has done this since new, although I didn't recognize it as an electrical issue for some months.

The factory battery was dead when I bought the tractor (had been sitting on their dealer floor for almost a year), so they put a new battery in when I picked it up. One thing I have observed is that the battery seems to lose charge slowly in-between uses. I've seen it get as low as 11.4 volts, which is probably low enough to cause the issues I'm having. Recharging does not correct the stumbling/dying problem, however.

The dealer from whom I purchased is 5+ hours away (they had one of the last XT3s left anywhere close to me), so taking it back there isn't viable. I did take it to a local dealer in the Spring (True Value) that sells a limited range of CC as well as does general lawn equipment repair. Naturally, it ran perfectly for them! He went through the wiring and said he replaced a couple of “sketchy” connectors. Ran fine all summer after that, but started acting up again after I pressure-washed it a couple months ago (not convinced there is any correlation there). Tractor is stored in a garden shed, so it doesn’t sit out in the weather.

I downloaded the 2000 series service manual yesterday, as it seems to be very similar to the XT3. It was very helpful to better understand all the components and how they're wired together. I’m going to run some additional tests today based on what I’ve been reading.

es

I've run all my tests on the RCM and safety switches, and everything checked out okay - a real head-scratcher.

One of the yootoob vids I looked at last night showed a guy that used jumper cables (negative side only) to jump directly from the battery (-) to the engine block to get around a bad ground issue. Decided it wouldn't hurt to try myself, despite my ohmmeter suggesting no issues there.

Danged if it didn't start right up!

Just finished lunch, so heading back out to pull it out of the shed, jack it up and see if I can find the battery grounding point and clean that up. I think I may go ahead and make up a direct ground strap, too. Hopefully this will be the permanent fix!

es

New ground strap is installed, direct from (-) to the engine block. Starts and runs fine! I drove it over to my garage and jacked it up to see if I could locate the frame end of the battery ground cable, but it still eludes me. Probably buried inside the frame under the operator platform.

I'll dig out the leaf vac tomorrow and give it a good stress test and will report back with results.

es

stembridge said:

New ground strap is installed, direct from (-) to the engine block. Starts and runs fine! I drove it over to my garage and jacked it up to see if I could locate the frame end of the battery ground cable, but it still eludes me. Probably buried inside the frame under the operator platform.

I'll dig out the leaf vac tomorrow and give it a good stress test and will report back with results.

es

Click to expand...

“Toaster” battery resistance tester is what I use on 250-350 CCA batteries to test. Sounds like ground issue may have resolved the problem. Now that you have experienced first hand how frustrating some of these issues can be for a shop to diagnose and fix, you can appreciate what they go through. Although in this case, experience would have probably sped up the process. Using jumper cables for good positive and negative connections is something I use from time to time to eliminate electrical problems.

I won't call this a permanent fix until I've run it numerous times without issue. I'll update this thread occasionally, hopefully with positive results.

Many, many thanks to everyone for their input!

es

Ran the tractor with the DR vac for a couple hours today and not a hiccup!



I think I found where the battery (-) terminates, at the base of the starter. Didn't pull it off yet, as I needed to get the yard done. Doesn't appear to have any corrosion on it, but we'll see what I find when I remove the bolt.

es

Look up on youtube the big 3 or big 4 upgrade. Talking about improving the wiring in cars and trucks with stereo systems pulling massive amperage. All circuits need testing UNDER LOAD. Engine off testing gets you na-da.

Need a good ground strap from the engine, frame and body. All tie together to the - battery post. The - battery post is the BEST ground location on any vehicle. Star grounding washers, buss bars and heavy cable are your friends.

Ran the tractor with the Johnny Bucket for ~30 minutes moving some topsoil into our kitchen garden area, no issues.



@slomo - my sleeve hitch and bucket lift motors are grounded directly to the (-) terminal for the reason you state. I've seen folks discussing the wiring upgrade on car sound systems, which makes a lot of sense.

es

stembridge said:

Ran the tractor with the Johnny Bucket for ~30 minutes moving some topsoil into our kitchen garden area, no issues.

View attachment 67241

@slomo - my sleeve hitch and bucket lift motors are grounded directly to the (-) terminal for the reason you state. I've seen folks discussing the wiring upgrade on car sound systems, which makes a lot of sense.

es

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Glad you got it fixed. I have seen loose engine bolts several times this year on customer equipment. Even with the ground on the loose engine bolt, the mower still started and ran. If in doubt I use sandpaper and wire brush to clean up corrosion.

Typically you want the starter body grounded to the - post. Why? Starter on many vehicles is the biggest amp draw on said vehicle. Now car stereos car easily surpass a car starter so things change with a mega car system. Glad to hear you got her fixed.

Had another session with the lawn vac today, about two hours or so. The tractor ran perfectly, and I have growing confidence the root problem has indeed been identified and corrected. I'll call it "fixed" at this point.

es

Most people look at the + cables and give up. Or check a fuse again being + in nature. Totally forget the - side of things.