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Diagnose my stalling JD x320 tractor?

4.8K views 16 replies 11 participants last post by  JoeZeppy  
#1 ·
My usually reliable 12-year-old JD x320 tractor started stalling this Spring. I’ve mowed about a dozen times since but the basic pattern is the same: starts fine, stalls out after 20-40 minutes with a single backfire. Sometimes it starts right back up, other times it won’t start until I let it sit for 15-20 minutes. I made it through one mow without stalling at all but every other time it stalled anywhere from about 2-6 times.

Like every other year, I had done the usual recommended winterizing maintenance last Fall, including new fuel filter and plugs, added dry gas, etc. This issue started on the very first mow this Spring, so I thought somehow moisture still might have gotten in the fuel. Over the first few mows, I used up the old fuel and ran down the tank as low as I felt comfortable doing before refilling with fresh fuel; it made no difference. Gas cap valve is fine, too. Something happens as the engine gets warmed up, apparently.

I’m not a particularly mechanical guy but am always willing to try to figure stuff out and fix myself, if possible. I'm looking for any leads on what is most likely going on and what I might be able to do about it.

Thanks in advance for your advice.
 
#2 ·
Welcome to MTF! Lots of info here and great members to help and share with. Two things come to mind, debris in the fuel tank clogging intake line and a bad coil. When it happens I'd pull the air cleaner and see if it is getting fuel in the carb. You can test by putting a small amount of fuel into the carb directly and see if it fires back up. If so, then likely something stopping fuel delivery. If not, then need to check the coil. I don't have the coil specs for your machine so hopefully someone that does will provide them.

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#3 ·
I second PA318guy's thoughts. Especially about a possible failing coil. Heat seems to exacerbate coil problems.

If the backfire is followed by total shut off, like you turned the key off, that would point toward ignition failure or a short somewhere that is killing the spark when it is warmed up.

The times when it fails to restart, you might check both the plug wires to see if any spark is present when cranking. If not, then look to the coils or the kill wire shorting to ground. If there is spark while cranking but no start, then look to fuel delivery issues.

If you engine has the fuel shut off solenoid, double check that it is staying open full time with the key in run or start position. That might be starting to fail. If it fails, it will also shut the engine down as if the key were turned off.

Just a couple of things that came to mind. Hope it is something easily found and fixed.
 
#4 ·
Thanks for these leads; this is very helpful.

Also:
  • The single backfire actually happens just after the engine goes dead. (Is that significant?) And, yes, when it stalls, it turns off quickly, like I've turned the key off.
  • I had to mow this morning and had a familiar experience:
    • started fine; half hour or so of mowing before it stalled + single backfire; immediately started again;
    • mowed for maybe 15 minutes and stalled again + backfire. This time it wouldn't start after 6-8 cranks so I pulled a spark plug, put the terminal end back in the cap and touched metal with the base and it immediately started even though, looking closely, I didn't see a spark. Turned it off, reinserted spark plug and it started fine again.
    • mowed for another 20 minutes or so, stalled, wouldn't start, did spark plug again with same result--immediately started :unsure: I have no idea what that might suggest.
    • had another stall later on but it started again immediately and I was able to finish the mow with no further problems.
I need to do some more homework. It sounds like coil issues are rising to the top of likely candidates and I may just go ahead and try to replace that myself after scouring YouTube for some how-to video.

Finally, any recommendation for parts source? My local dealer seems to have wildly inflated prices compared to what I see online but I want to avoid cheap knock-off stuff that will fail.

Again, thanks for the info.
 
#9 ·
Fuel vapor in the exhaust, implies that the spark has stopped before the fuel flow into the cylinders has stopped.
The half dozen or so revolutions after the key is turned off, continue to pull fuel air mix into the cylinders after the spark has been shut off. After a few revs it gets into the hot exhaust and can explode there as a back fire.

It is why fuel shut off solenoids were installed on carbs. To stop the fuel/air flow at exactly the same time as the spark, that way as the engine revs wind down they don't pull fuel air mix into the cylinders.
 
#12 ·
Mine as well. I'd disconnect the kill wire as a next step - if it continues to run fine, it's the ECM. If that doesn't fix the issue, it's likely a coil.

If you do need a coil, my $0.02 is to skip the cheap eBay coils.
 
#13 ·
This is very frequently the ECU (aka ECM). I've replaced it on 4 different tractors with the same symptoms. It's one bolt and one wire harness, easily accessible right under the dash. About $100. It's a known issue with the x300 and x500 series. As mentioned above, when it happens, pull the kill wire. If it starts back up, it's the ECU.

Taryl Fixes All has a YouTube video on the test
 
#14 ·
Finally had a chance to disconnect the kill wire and give it a try.
An hour of mowing with no problems whatsoever. When finished I turned off the key and hopped off the mower and it ran for a couple of seconds before shutting down (which it never does).

It seems like replacing the ECM is the next step.

Thanks again for the tips.
 
#15 ·
A final post for those who might find this thread looking for a solution to their own problems.

I had to order the ECM from my dealer; $104. I reconnected the kill wire, installed the new ECM, which is very simple, (video here), and mowed for an hour and a half straight with no problems. Looks like I'm good to go.

Thanks again to folks who helped with advice.
 
#17 ·
I wanted to extend my neighbor's thanks for this thread. He has been having a very similar problem with his X320 (also 12 years old, interestingly enough) running rough this summer and when I happened upon this thread, I emailed it over to him. He did some diagnosis, ordered and installed a new coil, and he's good to go!
 
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