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John Deere 790 cannot turn off

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grindn1
Join Date: Sep 2011
Posts: 6 sidney
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2011-09-28          180610


I have a john deere 790 diesel 30 hp and hadn't been started in a couple of months so I had to charge battery. Used it for approx. 30 minutes and turned key off but tractor kept running. Could use any info or advise. thanks



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John Deere 790 cannot turn off

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auerbach
Join Date: Sep 2007
Posts: 2168 West of Toronto
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2011-09-28          180612


Diesels ignite from compression, not from ignition (there are no spark plugs and such), so are usually stopped by fuel shut-off. A few models will shut off the fuel when the key is turned off but on most you pull the throttle to off and have to remember to switch off the key, either before or after the engine stops. In fact, once started, you could turn the key off and run it all day like that. ....


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grindn1
Join Date: Sep 2011
Posts: 6 sidney
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2011-09-28          180621


Thanks a bunch auerbach. So with a 2002 model that is not a rare thing ? Actually I was getting ready to sell it and buy a front mount zero turn yesterday when this happened.Before this incident I have never had any problems with it. Being a girl its more than I need, I just want something simple. So is there another solution so it will shut off by the key ? I called potential buyer and explained what happened and want to make sure it is not acting up. I read manual and researched it for hours and I thought it was the fuel shut off solenoid. I'm thankful it isn't. Thanks so much for ur time. ....


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grindn1
Join Date: Sep 2011
Posts: 6 sidney
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2011-09-28          180624


Well I did just as you instructed me to and it won't shut off that way either. Could it be the ignition, fuel shut off solenoid, electric problems ? I checked the seat safety switch and thats not the problem. also listened for the clicking sound from fuel solenoid with key in on position without starting and solenoid has passed that test. Sure hope someone can help so I can get something smaller and easier. Thanks again
....


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auerbach
Join Date: Sep 2007
Posts: 2168 West of Toronto
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2011-09-28          180626


Not familiar with that model, but if you pulled the hand throttle to zero and it keeps running, I'd guess there's something amiss in the linkage. As for the seat switch, isn't it supposed to cut the engine if your weight is off it? And if there's a key-switch-operated fuel-cutoff solenoid that doesn't work, I doubt it would take much to replace it.

Until you get it sorted out, you can stop it by stalling it or by using the decompression control, but neither is easy on the tractor. ....


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grindn1
Join Date: Sep 2011
Posts: 6 sidney
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2011-09-28          180635


Thank You Very Much for the help. Have a good day. Oops one more thing. Can a fuel shut off solenoid be tested? Just don't want go out and buy one and that maybe not be the problem. Have A Great Day ....


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auerbach
Join Date: Sep 2007
Posts: 2168 West of Toronto
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2011-09-30          180648


No moving electrical apparatus is easier to test than a solenoid. It has just one action, usually an obvious one, in response to current applied or (as in this case) current withheld. You just need a 12V source and a couple of leads, once you find and preferably remove the solenoid.

I don't know how the mechanical connection from the solenoid cuts the fuel. Maybe what's stuck is the solenoid, or maybe it's the fuel gizmo. You might start by getting the service manual for your model. ....


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kthompson
Join Date: Oct 2005
Posts: 5275 South Carolina
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2011-09-30          180651


Certainly may be way wrong here and don't know JD tractors at all, been years since used the only ones ever have sat on.

I would be surprised for the seat safety switch to cut off the engine on any tractor (unless it has to do with PTO also engaged). Prevent it cranking yes but not cut if off.

Second the diesels I am familiar with not sure have the fuel cut off the way describe here. I read it as you push (or pull) the throttle to idle and then lower and it cuts the fuel. If misunderstanding apology already given. Now a separate "PULL" knob yes but not directly part of the throttle control for engine speed use.

Look in the manual for manual or emergency shut off. If you don't find something there it may not have a manual cut off. If you find nothing in the manual or don't have a manual look very carefully at the dash and below it for a small knob that you have never used before. Normally they have to be pushed back in by hand. Many tractors use to have only that way to cut the engine and no electrical solenoid at all.

If you must kill it and the air intake allows it place something that will prevent air flow through and it should cut right off.

Again , no idea on this tractor but see if you can find the solenoid. Depending on the design there might be some linkage loose, limb or such jamming it preventing movement or a spring missing that pulls it shut.

Hope this helps. ....


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billtreat
Join Date: Oct 2011
Posts: 21 los alamos calif
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2011-10-03          180671


I have a kobota L3410 that does the same thing found out it will not shut off unless the battery is charged. ....


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jdgreen
Join Date: Jul 2003
Posts: 232 Maryland
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2011-10-12          180839


Here is the theory of operation from the tech manual.
Maybe it will help you to understand how it works.

Engine Shutoff Circuit Operation
Function:
To prevent the machine from being started or left running in
an unsafe condition.
Operating Conditions:
• Operator on seat.
• and/or;
• Gear range lever in neutral position, PTO Switch Off.
• Park brake locked.
Theory of Operation:
The starting motor will crank when current is provided from
the battery.
Battery current is provided through the starting motor
solenoid contacts when operating conditions are met.
If the operating conditions are not met, the engine will not
start as fuel will not be delivered to the combustion
chambers. See “Cranking Circuit Operation” in this chapter.
Fuel is supplied to the engine through the operation of the
K2 fuel relay and the Y2 Fuel shutoff solenoid, provided
that operating conditions are met.
If the operating conditions are not met, fuel is not supplied
and the engine will not start or run. See “Fuel Supply
Operation” in this chapter.
When the operating conditions exist, the control module
provides battery voltage to the K2 fuel relay, Y2 fuel shutoff
solenoid, and K1 start relay.
The energized fuel relay coil closes the relay contacts and
the closed contacts provide a current path to the fuel
solenoid pull-in coil.
The Y2 fuel solenoid opens, fuel is provided to the engine
and ignition can occur.
The A1 control module provides a power circuit for the fuel
solenoid hold-in coil.
The power circuit through the control module is a 0.5
second timed delay circuit.
If the operator leaves the seat for more than 0.5 second
without engaging the park brake and placing the gear
range lever in neutral with the PTO switch off, the circuit
stops voltage to the hold-in coil, the fuel solenoid deenergizes
and fuel is shut off to the engine.
With the gear range transmission in the neutral position,
current flows through the S4 transmission neutral switch to
the S3 PTO switch and then to the A1 control module
indicating the machine is in neutral.
When the operator is off the seat, battery voltage to the A1
Control module is routed to the S4 transmission neutral
switch through the 450 Wht/Blk wire to a 3 Amp fuse in the
F4 fuse block, through the 602 Blk/Blu wire, to the 610 Blk/
Grn wire, and then to the S4 transmission neutral switch.
From the transmission neutral switch, current is routed
through the switch and the 609 Blu/Yel wire to the S3 PTO
Switch. From the PTO switch, current is routed to the A1
Control Module via the 613/603 Blu/Red wire.
The operator may start the machine while off the seat if the
gear range selector lever is in the neutral position
(transmission neutral switch closed), the PTO switch is in
the Off position and the seat switch is in the Defeat
position. In this condition, current flows to the S2 seat
switch defeat contacts from the A1 Control Module via the
606/607 Blu/Yel wire. From the S2 seat switch current flows
through the 600/614 Blu/Yel wire directly to the A1 Control
Module. Current also flows from the Defeat Switch contacts
through the 608 Blu/Yel wire to the 609 Blu/Yel wire and
then to the S3 PTO switch. From the PTO switch the
current follows the 613/603 Blu/Red wire path back to the
A1 Control Module.
With the engine running and the S2 seat switch in the
defeat position, the PTO may now be engaged. This
eliminates the 603 Blu/Red wire current input to the A1
Control Module from the PTO switch. The current input to
the A1 control module now comes exclusively from the S2
Seat switch defeat contacts via the 600/614 Blu/Blk wire. ....


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