6310 Blown fuse- STUMPED!!

[rutwad]

JD 6310 2wd OOS blows the 30amp main fuse. Tractor will crank and run for some time, then fuse blows and tractor shuts down just like it was shut off. Stick a fuse in, crank it up, and it blows again. Wait some time and start tractor, then it will run for some time again before blowing fuse.

I did read where a temperature sensor could be bad and causing trouble. There is an electrical plug in the housing where the radiator hose attaches to the enigne, but no wires or plug. The closest plug is just under it at the front side of the fuel pump assembly. Unplugging this will cause the tachometer to not work, but the tractor will run.

ANY IDEAS???

 

[Matt_Jr]

Does anyone have a wiring diagram? I would start off with a visual inspection of the wiring harness. Look for any places where the harness could rub on a bracket, frame, or moving parts. Try pluging in the fuse without starting the tractor and shaking any wiring to see if the fuse blows. Is there a way you can find out what the main fuse supplies power to? That's what I need the wiring diagram for.

 

[Rob-D]

Hi Rutwad,
I'm an EE and have been trouble shooting stuff for over 40 years.Here's what you do:

Matt had a good idea, what you want to do is get a 12 volt bulb, car running lights are good. Now put it in an old socket with wires on it and put it in place of the fuse (pull the fuse out). Now pull and push around on the wires with the key on to see if the bulb lights. If it does you know your short is back. Sometimes you can locate exactly where it is just by moving wires and watching the bulb.
The bulb might light dimly but this is most like normal current runnintg through the circuit, wait till it lights relatively bright.

If you think it's the termo-switch leave the tractor on for a while and see if the bulb lights with it cold. If it doesn't then heat up the tractor and see if it comes on then. You don't want to leave the tractor on too long though when it's not running so don't do this often.
The wire you pulled is from the tach not the termo.


Rob

 

[Matt_Jr]

That's a good idea Rob. I'll have to use that at work. I've never thought of using a bulb in place of a fuse. I usually use a short finder, but usually as a last resort 'cause I usually find the short and don't have to use it. A set up with a light bulb in place of the fuse. Genius.

 

[rutwad]

I love the bulb idea!! Simple, but something I never would have thought of.

Unrelated, but what actually makes the diesel engine stop running when the key is shut off. Does it just shut down the fuel pump?

THANKS FOR THE QUICK REPLIES!!

 

[kennyd]

Unrelated, but what actually makes the diesel engine stop running when the key is shut off. Does it just shut down the fuel pump?

THANKS FOR THE QUICK REPLIES!!

There is a fuel solenoid mounted to the injection pump that's energized when the key is on letting the fuel flow. No power to the solenoid, no fuel can flow and the engine will not run.

 

[kebo]

I love the bulb idea!! Simple, but something I never would have thought of.

Unrelated, but what actually makes the diesel engine stop running when the key is shut off. Does it just shut down the fuel pump?

THANKS FOR THE QUICK REPLIES!!

I asked that question sometime ago regarding a JD 750 that I used to have, compared to the JD 790 that I have now. With the 750, the only way you could shut it off was to push the throttle ALL the way forward, which would shut off the fuel supply being pumped out of the injector pump. Turning the ignition off had NO effect on the motor once it was running. You could even take the key out and put it in your pocket and ride the tractor all day long without it.

But now on my 790, when you switch off the ignition and remove the key, it shuts the motor off just like with an automobile. I'm not a diesel mechanic but I think the fuel pump is integral to the diesel injector pump. I believe there is a solenoid that controls a valve in the fuel line which closes off the fuel supply to the pump when the key is switched off. I'm sure that if I'm wrong, one of the diesel experts here will correct me.

 

[rutwad]

I have been working on the tractor all day- in my mind only, not physically. I am no mechanic, but I think it must be a safety switch causing it to shut down. Maybe temp, oil pressure, etc. But would it also cause it to blow a fuse?

 

[jenkinsph]

You may have two separate problems, a bad safety switch and a dead short somewhere but the probablility of there being a destroyed and shorted safety switch is very low. It is more liikey you have a short in the wiring or connections, I would proceed to check out the wiring tracing out the path of the wiring downstream of the blown fuse.


Steve

 

[kebo]

I'm an electronics tech by degree and it sounds to me like your problem is not a "dead short" per se, but rather what we call a "high resistance" short. If it were a dead short, then it would almost certainly blow the fuse as soon as you switched the tractor on, UNLESS you are using 30 amp slo-blo fuses. These will permit an overcurrent condition for a period of time before the fuse heats up enough to open up.

Going by your description in the original post, it doesn't sound like the problem is in the wiring. It sounds to me more like some component in the electrical circuit is drawing excessive current, which eventually overheats the fuse causing it to open up. You might try and see if you can feel if something getting hot about the time the fuse blows. Maybe you have already found the problem by unplugging that sensor?? You did say that the tractor ran after it was unplugged, I'm assuming you meant it didn't blow another fuse then?

Whatever is causing the fuse to blow will stop doing it after you let it cool down for awhile so in my mind, that is a component that is heating up and then drawing excessive current. A wiring diagram would definitely help you see all the components in the circuit that could potentially cause the main fuse to blow. Good luck finding it!