3930 will not sart

[daycab]

Hi
I've got a '96 NH 3930 that will not start. If I jump the fuel pump solenoid, it starts right up. I've checked the neutral safety switch and the PTO safety switch and ruled these out as culprits. I may be mistaken, but both of these safety switches prevent the starter from turning, not the fuel pump solenoid from opening. Any suggestions are greatly appreciated.

 

[Jerry/MT]

Hi
I've got a '96 NH 3930 that will not start. If I jump the fuel pump solenoid, it starts right up. I've checked the neutral safety switch and the PTO safety switch and ruled these out as culprits. I may be mistaken, but both of these safety switches prevent the starter from turning, not the fuel pump solenoid from opening. Any suggestions are greatly appreciated.

Without knowing what the circuit diagram for your tractor looks like, I'd guess the fuel solenoid is accuated by current from the run and the start part of the starter switch. If you have to jump it to get it to work, then I'd suspect you'll have to look at the circuit from the key switch to the solenoid to find the problem.

 

[whodat526]

check the relay that is where i would start first and does the fuel pump kick on when u turn the key on

 

[daycab]

Thanks for the suggestions! The problem could very well be a grounded fuel pump solenoid wire. To farther complicate matters, here are the details of this starting failure.

The man that feeds my cattle when I'm not here complained the tractor was hard to start and cut off on him several times while feeding. I used the tractor the next day and found his concerns to be true. I plugged in the block heater and eventually got the tractor to start. The ride to the cattle was downhill and it ran fine until I tried to pull a grade. As soon as the tractor headed uphill, it would not start. Coasting back to level ground, the tractor would start, but wouldn't continue to run. Since the fuel tank had been recently filled from the bottom of the transfer tank in my pickup, I suspected a clogged fuel filter. I replaced the filter, charged the battery, and replaced some bad fuel line washers, thinking the fuel pump may be sucking air through the brittle fittings. No luck. Despite my reluctance, I gave the motor a small dose of ether, and was able to get it to fire but not run. Definitely fuel starved.

The back of the ignition switch is virtually invisible. There is no clearance and no free play in the wire harness to bring the ignition switch to view. The cowl appears to be an exercise in part removal, the steering wheel, throttle control, as well as the forward/reverse directional lever need to be removed to gain clear access to the back of the ignition switch.

Should I proceed? Or whimp out and call the dealer with his high dollar roll off and mechanics?

 

[jinman]

Does your tractor have a seat switch? These usually only operate or disable the fuel solenoid. If the switch has frozen water in it or is going bad, it may be the source of your problem. As you suggested, the neutral and PTO sensing will not allow the engine to crank over, but the seat safety switch will allow the engine to crank but fuel is not supplied by the solenoid. Many times you can set the parking brake and then select neutral to bypass the seat switch. At least that's how it works on my tractor. That will allow you to start the tractor without anyone being in the seat.

 

[Jerry/MT]

Does your tractor have a seat switch? These usually only operate or disable the fuel solenoid. If the switch has frozen water in it or is going bad, it may be the source of your problem. As you suggested, the neutral and PTO sensing will not allow the engine to crank over, but the seat safety switch will allow the engine to crank but fuel is not supplied by the solenoid. Many times you can set the parking brake and then select neutral to bypass the seat switch. At least that's how it works on my tractor. That will allow you to start the tractor without anyone being in the seat.

Respectfully, what's the logic that allows the engine to crank but the solenoid valve will not supply fuel when you're not on the seat. I would have thought the all the "no start unless all switches are in the correct position" prevented the starter from actuating. Is the seat switch a "deadman" switch? if so, the tractor would shut off when you stood up and streched.

 

[jinman]

Respectfully, what's the logic that allows the engine to crank but the solenoid valve will not supply fuel when you're not on the seat. I would have thought the all the "no start unless all switches are in the correct position" prevented the starter from actuating. Is the seat switch a "deadman" switch? if so, the tractor would shut off when you stood up and streched.

Yes, there are two separate safety systems. One is neutral sensing and the other is operator presence. My tractor does exactly as you said. If you are operating and stand up, the engine dies. You can crank the engine, but it won't start. If you put the range in neutral and set the parking brake, you can stand up because that bypasses the operator presence system. When the OP said his tractor was cutting out while his neighbor operated it, that sounds to me like a defective seat switch on its last legs and making intermittent contact. That's exactly the symptoms that I would expect.

I'm making an assumption that the 3930 is very similar to my tractor in operation since it seems the safety circuits are similar from the original post. As easy as it is to check the seat switch, that would be my starting point because I know it is common for NH to disable the fuel solenoid.

 

[thclimer]

Respectfully, what's the logic that allows the engine to crank but the solenoid valve will not supply fuel when you're not on the seat. I would have thought the all the "no start unless all switches are in the correct position" prevented the starter from actuating. Is the seat switch a "deadman" switch? if so, the tractor would shut off when you stood up and streched.

On my TC33D once its running the seat switch utilizes a timer before it shuts off the tractor; it seems like its 3 seconds then it shuts off. Like Jim stated if you are not in the seat and the parking brake is locked on it ignores the seat switch and allows you to start the tractor as long as other safeties are met.

 

[whodat526]

no seat switch on a 3930

 

[jinman]

no seat switch on a 3930

Well that pretty much shoots the heck out of my theory, doesn't it?:laughing:

EDIT: I just did a search and found that several people on SSB Tractor site have reported faulty ignition switches where the fuel solenoid was powered in Run position, but dropped out in Start position. They also mention loose connections at the fuse block and even several with mouse-eaten wiring. All things that can be checked without calling the dealer for an expensive tow and repair.