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  1. #1
    Silver Member DWCox's Avatar
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    John Deere 790

    Default 790 Fuel Solenoid Fuse Problem

    Hi,

    I have a 2005 JD 790 with only 60 hrs. on it. Today I went to start it after not running for two weeks and the battery appeared dead. Since it is 3 years old, I pulled the battery, used baking soda and water on all terminals, cleaned everything shiny--including the ground wire to the frame, terminal ends, etc., and coated it with all purpose grease. I added a bit of distilled water into each of the cells, installed everything and then jump started it from my truck.

    Everything was fine as I allowed the tractor to idle--until I turned the front headlights on. Within a couple seconds, the lights went out and the engine died. Could not jump start it for anything. Finally checked the fuses, and sure enough the fuel solenoid fuse was blown (3 amp). I put in a new one, and jump started it again. It was running fine, and out of curiosity I turned the headlights on again--the engine immediately died. Checked the fuel solenoid fuse and it is blown again.

    I have never had this problem before. All the other lights (hazard, blinkers, etc.) all work fine and do not negatively affect the fuel solenoid fuse.

    Any thoughts on why the front headlight circuit is blowing this fuse?

    Thanks in advance.

  2. #2
    Veteran Member Rara Avis's Avatar
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    Oct 2006
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    John Deere

    Default Re: 790 Fuel Solenoid Fuse Problem

    Don't start the tractor, but try turning the key to the ON position and then turn on the headlights and see if the fuse blows...

    If the fuse doesn't blow
    Check the solenoid
    Fuel Solenoid Gound Test
    1. Key off
    2. separate connector at solenoid
    Check continuity between harness side of connector and ground at battery negative post
    Must be 12vdc...if so replace solenoid otherwise poor ground...clean and repeat
    Fuel Shutoff Solenoid Holdin Test
    1. Turn key on
    2. push solenoid in and release...It MUST STAY IN
    If it doesn't proceed...
    Fuel Shutoff Solenoid Voltage Test
    1. Turn Key on
    2. Check for voltage at connector to solenoid...should be at least 9 volts
    If not, reverify your ground and if that's okay...REPLACE SOLENOID
    Last edited by Rara Avis; 07-27-2008 at 07:32 PM.

  3. #3
    Elite Member
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    Default Re: 790 Fuel Solenoid Fuse Problem

    I checked the schematic in my tech manual and neither 3 amp fuse goes to the fuel solenoid.

    Mines a couple years newer, could they have changed that much ?
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  4. #4
    Silver Member DWCox's Avatar
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    John Deere 790

    Default Re: 790 Fuel Solenoid Fuse Problem

    Quote Originally Posted by Willl
    I checked the schematic in my tech manual and neither 3 amp fuse goes to the fuel solenoid.

    Mines a couple years newer, could they have changed that much ?
    With mine, the fuel solenoid and control box (together) are listed (see below) under fuse "B" as 3 amp. When this fuse blew, the tractor wouldn't start; when I replaced it, it started right up.




    I tried some of the troubleshooting tips for the fuel s. but it was a bit difficult due to the apparent state of the battery. So I linked the jumper cables from my truck to the battery to supplement. So far I have observed that the fuel solenoid fuse does not pop when I switch the headlight switch on without the engine running. Likewise, I also measured voltage going to the solenoid. There is also voltage going to the headlights--though I disconnected the connectors from the headlight bulb wires and simply read it with my meter.

    I started the tractor up, disconnected the jumper cables and, interestingly, shortly after I switched the headlight switch to the on position the engine cut off. I am going to replace the battery with something new (since this is an 05).

    Is it possible that this entire problem will clear when a new and fully charged battery is reintroduced? I need to get the service manual on this tractor, but does anyone know that if a battery is dead and incapable of taking charge from the alternator, can instabilities of this nature emerge? I wonder along these lines since something like the headlights do require a fairly significant draw of electricity.

    Again, any input is appreciated.

  5. #5
    Elite Member
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    Default Re: 790 Fuel Solenoid Fuse Problem

    Ya, I see that page in my manual now.
    Last edited by Willl; 07-28-2008 at 02:45 AM.
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  6. #6
    Elite Member
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    Default Re: 790 Fuel Solenoid Fuse Problem

    Flipping your headlights on with a weak battery could shut down your engine.

    Shouldn't pop your fuse though.
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  7. #7
    Silver Member DWCox's Avatar
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    John Deere 790

    Default Re: 790 Fuel Solenoid Fuse Problem

    Quote Originally Posted by Willl
    Flipping your headlights on with a weak battery could shut down your engine.

    Shouldn't pop your fuse though.

    Thanks for including the wiring schematic. Very helpful.

    I will put a new battery in tomorrow as a fresh base line and see what happens.

  8. #8
    Gold Member
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    Default Re: 790 Fuel Solenoid Fuse Problem

    DWCox,

    Before plunking out $60+ for a new battery, you might want to remove the old battery from the circuit (you're going to have to remove it anyhow) and connect jumpers from a good battery (no need to disconnect it from the other vehicle, just don't start that vehicle) to the battery cables on your tractor. Then see if you still have the same problem. If the problem still exists, you may have an alternator problem (but I think it's much more likely it's the battery). If the problem is gone, then buy the new battery with confidence.

    If the battery is bad, it could be pulling the voltage of your whole system down. Here's how that could have caused your problem: Suppose your fuel solenoid requires 30 watts power to operate. Since watts = amps x volts, then 30W = 12V x amps so amps = 30W/12V = 2.5 amps. If a bad battery dropped the voltage to 10 volts, then the 30 watt solenoid would be trying to draw 3.0 amps, enough to blow the fuse.

    Another (remote) possibility is that low voltage is confusing the time delay control module causing it to do something that causes your fuse to blow.

  9. #9
    Silver Member DWCox's Avatar
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    John Deere 790

    Default Re: 790 Fuel Solenoid Fuse Problem

    Quote Originally Posted by TedLaRue
    DWCox,

    Before plunking out $60+ for a new battery, you might want to remove the old battery from the circuit (you're going to have to remove it anyhow) and connect jumpers from a good battery (no need to disconnect it from the other vehicle, just don't start that vehicle) to the battery cables on your tractor. Then see if you still have the same problem. If the problem still exists, you may have an alternator problem (but I think it's much more likely it's the battery). If the problem is gone, then buy the new battery with confidence.

    If the battery is bad, it could be pulling the voltage of your whole system down. Here's how that could have caused your problem: Suppose your fuel solenoid requires 30 watts power to operate. Since watts = amps x volts, then 30W = 12V x amps so amps = 30W/12V = 2.5 amps. If a bad battery dropped the voltage to 10 volts, then the 30 watt solenoid would be trying to draw 3.0 amps, enough to blow the fuse.

    Another (remote) possibility is that low voltage is confusing the time delay control module causing it to do something that causes your fuse to blow.
    Thank you very much! That is very helpful and makes a great deal of sense. I think it is going to be right on target.

    Very good idea on swapping out the car battery first as well for added confidence.

    I likewise do not think it is the alternator since checking whether it was working was the reason I turned the lights on in the first place. The headlights would increase in intensity as the rpm levels went up.

  10. #10
    Elite Member
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    Default Re: 790 Fuel Solenoid Fuse Problem

    Quote Originally Posted by TedLaRue
    then the 30 watt solenoid would be trying to draw 3.0 amps
    Using your 'math', what kind of amp draw would you get at 1 volt ?


    Edit; remember, you can't change the resistance of the coil in the fuel solenoid.
    Last edited by Willl; 07-28-2008 at 02:39 AM.
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