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My x304 battery ws dead so I thought I'd jump it. The mower started up fine and ran with the jumper cables off. Once I took the cable off the mower died & Wouldn't turn over. I got a new battery for it now the motor turns over but it won't fire/start. I'll replace the spark plug in the morning. If that doesn't solve the problem what's the next step? I haven't a any problems starting the mower before (if that helps). I'm fairly handy but dumb troubleshooting small gas engines.
Thanks!

Get the Technical Manual from JD & follow the step by step instructions for checking the charging system.

Didn't have to do that! Several videos on youtube described my symptoms excatly. The interlock module / ecu ... got fried when I jumped it with the truck. The lawn mower couldn't handle the amps from the truck. DON"T JUMP START LAWN MOWERS FROM VEHICLES!! Part is AM141075 about ~$100.00, It's located under the 'dash'. one 10mm bolt holds it on to the hood. Simple but expensive fix. Video said even battery chargers .... could fry the module.

Just a bunch of bull. The X304 already comes with a 350 CCA battery. Plus the electric and electronics will only pull the needed amperage and no more. Otherwords just a 850 CCA battery is connected doesn't mean the mower is going any more amps then needed. 12vdc is 12vdc.

Now the solenoid shift starter can pull up 300 amps in a bind but it pulls under 250 amps normally. The only a good pulls more is if your connect a higher voltage battery such as a 24 VDC one.

But if you even momentary connect a battery backwards it will fry the electronics very quickly.

Btw I use a 600 and a 800+ CCA (my S1500 truck) automobile battery to start mowers when they have bad batteries.

ts1520 said:

Didn't have to do that! Several videos on youtube described my symptoms excatly. The interlock module / ecu ... got fried when I jumped it with the truck. The lawn mower couldn't handle the amps from the truck. DON"T JUMP START LAWN MOWERS FROM VEHICLES!! Part is AM141075 about ~$100.00, It's located under the 'dash'. one 10mm bolt holds it on to the hood. Simple but expensive fix. Video said even battery chargers .... could fry the module.

Click to expand...

Total and utter rubbish spread by idiot morons trying to prove they have a brain in the empty void between their ears rapidly being filled by their over inflated egos.
A circuit draws what it draws regardless of the size of the battery connected to it
Where problems come in is if the VOLTAGE is out of specification.
Think about it
You have 100-200 A in the wires coming to your house but does that blow your toaster to bits ?

What kills interlock modules is usually a failue in the potting mix which allows water to get in & cause a short , or reversed voltage if it is not polarity protected

"Well 'cuse me for livin" (as my grandmother used to say.)

The mower is stored in a shed & started fine before. I connected the jumper cables correctly (double checking before I attached them). The mower started when jumped and immediately died when I took the cable off. The motor would turn over but not fire when I tried to start it after that. I looked at the videos, bought a new module (~$100 at the JD dealer). Put it on and the mower starts fine now.
So I guess I'm an idiot too for following a youtube suggestion and happened to work for me.

ts1520 said:

"Well 'cuse me for livin" (as my grandmother used to say.)

The mower is stored in a shed & started fine before. I connected the jumper cables correctly (double checking before I attached them). The mower started when jumped and immediately died when I took the cable off. The motor would turn over but not fire when I tried to start it after that. I looked at the videos, bought a new module (~$100 at the JD dealer). Put it on and the mower starts fine now.
So I guess I'm an idiot too for following a youtube suggestion and happened to work for me.

Click to expand...

No it had the problem that was diagnose correctly. It is the explanation as to why it fail that we are questioning as these mowers have 300 CCA or larger batteries in the first place which if they are correct would blow the module everytime you install even a new fully charged mower battery.