John Deere 790 stuck in the middle of the field, dead, won't stay running.

[Matt621]

Bought a used 2006 790 with 600 hours on it. It worked at first fine. But then I started having troubles. Initially it was the seat switch. So I fixed that. But today it just kept dying. I thought it was the seat switch again so I bypassed it. Okay, once I did that it would start. But the moment I put in gear (clutch in) it'd kill the engine. If I engage anything to the engine it would die. The I recall I had trouble with the parking brake. So I engaged it and disengaged it several times. Finally it started working. For about 30 feet. Then it died. Then it started again.... lifted the bucket, started to dump then it died again. And on and on and on. I finally just left it in the field and walked home. I'm sick of it.

If it'll start it'll idle and rev fine. It'll go to red line or sit idling as long as I ask it to. It only dies when putting it into gear or if it's in gear moving then it'll just die while moving and won't start again.... until it decides it will.

I'm covered in dirt and dust, going to take a shower. If anyone has any ideas on what is going on, please lmk. I can't find much online in the way of wiring or diags, it's all just simpleton stuff on how to verify things are working (same for the manual.)

I'm very mechanical, but totally unfamiliar with this JD stuff.

Thanks

 

[LouNY]

One way would to be remove the fuel shutoff solenoid, or figure the proper way to bypass all the safeties.

 

[Matt621]

If i knew were all the safety switches were and have a wiring diagram that's exactly what I'd be doing. But so far I can't find that information online.

 

[Wagtail]

G'day Mate and welcome to TBN from Downunder.

Not knowing where in the world you are, a suggestion is to visit your 'local' JD Dealership and ask their Parts Department for copies of the relevant wiring diagrams you require... they'll print them off for you at no charge. (I know that my dealership will and has done this for me) My dealership will also grab a mechanic out of the shop to discuss any fault I may have, again, no charge.

Enjoy the site.

 

[Matt621]

I'm out in the sticks. At least an hour away from anything like a JD dealship but Monday i'll call one and see what I can get. I'm just shocked it's not available online. There are a zillion people searching for John Deere safety switch but very little information and none on the version I have. I took apart the seat switch but it's not it. It's as soon as I engage the transmission or PTO.

 

[DieselBound]

When you engage the PTO you're not in gear? Any difference if depressing the brake (there may be a switch here for the safety circuit).

There's circuit logic. Might be that some sensor/switch that is expected to be disengaged/engaged isn't in the proper state.

I'm thinking that Lou probably has the right call, that it's the fuel shutoff solenoid. I think that you could watch to see what's happening (mechanical action): could also put a meter on it and see what it's doing).

Have to wonder how many injuries there have been trying to diagnose issues like this? "Safety" stuff causing accidents!

 

[Matt621]

The problem is actually two fold.

#1. just to get it started is a hit or miss. Right now it won't even start regardless of anything I do... then randomly it'll just start like nothing was ever wrong. So that's part one.

#2. Once I do get it started it runs great. Until I try to engage anything. Any gear or the PTO. Anything that would normally transfer power to something. The hydraulics work fine. (bucket).

 

[Matt621]

Anyone have a list and location of all the safety switches on this thing?

 

[DieselBound]

Hit and miss always has some pattern. Until you get a schematic I'd suggest doing a lot of detailed troubleshooting via manipulation of various actions (thermal cycles; ignition switch jiggling, moving levers etc.).

If the hydraulics work then it's not load-related (and unlikely fueling issue). It would seem to be safety-related as gear and PTO operation are generally things that are in safety-circuitry.

My Kubota B7800 has a really hit and miss start operation that is related to its clutch engaging a safety switch (the switch is in an impossible location, so I just kind of tolerate this issue). It doesn't, however, affect continued operation once running.

I'd pull EVERY fuse and test. Look at connections and re-seat. Do the same for every safety switch. Fragile electrical connection means a voltage drop. Not enough voltage on a circuit will alter switching.

I'd bet that you could find every switch if you put on your detective hat. Wires and link rods tend to meet at switches.

 

[5030]

Is it insured? If it is, roast it and get the payoff on it.

 

[LouNY]

Or just remove the fuel shutoff and see if she will start,
just be aware it will not shutoff if it starts.
So low idle high gear stall it.

 

[Richard]

I'm not familiar with your tractor. I had some similar issues with my JCB (except I couldn't take it to higher RPM's sitting still for a "long" time)

Upshot for me, I have a water separator bowl under/near the fuel filter. Turned out for me, the separator was full of water so I only had a sliver of fuel residing on top of it. As long as my demands were pretty small, it would trickle through fine. Once I created any kind of real demand (like drive across the field) it would die and 15/20 minutes later, it would start again and idle perfectly fine....but once the demand was created, it would die again.

I was a bit embarrassed when I discovered it was choc full of water. I don't check that too often (like never it would seem!)

 

[ranger danger]

The problem is actually two fold.

#1. just to get it started is a hit or miss. Right now it won't even start regardless of anything I do... then randomly it'll just start like nothing was ever wrong. So that's part one.

#2. Once I do get it started it runs great. Until I try to engage anything. Any gear or the PTO. Anything that would normally transfer power to something. The hydraulics work fine. (bucket).

#1 i can't help with but, #2 sounds like the safety switch under the seat. I'd try hotwiring that switch.

 

[Chewwy]

JD 790 wiring diagram

does anyone have access to a wiring diagram for a 2002 JD 790 tractor? closest i can come to one is buying a $180 shop manual. thank you

www.tractorbynet.com

 

[LouNY]

Post #6 of the thread linked above is the wiring diagram;
https://www.tractorbynet.com/forums/attachments/790_electrical-jpg.457134/
this may get you to it.
Interesting to me is that this uses a time delay unit to control the fuel solenoid.
Makes me wonder if it is using power to shut off the engine by activating the fuel solenoid.
It seems that your tractor has several safety switches,
A neutral start relay, but you are cranking so that seems to be working, controlled by the time delay unit.
Then a seat switch, a mid pto switch, a rear pto switch and a neutral switch which tie in with the delay unit.

 

[CobyRupert]

Do you know how safety shutdown normally worked? Did they work?
Interlocks may include some combination of seat switch, neutral switch, parking brake and pto switch, etc... Usually an empty seat switch shuts tractor down, but an empty seat switch may be canceled out by a parking brake (set) switch, or only work in combination with another switch.
I can’t think of a scenario where if a switch other than the seat switch failed that it would shut down the tractor.
Seems like all roads lead back to the seat switch.
…now if the brake switch , PTO switch, neutral switch (or whatever) also fails (or sticks closed) intermittently, tractor may not shutdown for the broken seat switch because it erroneously thinks the parking brake switch is still set, or the pto is off, etc..(a case where two wrongs make a right).
Then when the other switch intermittently corrects itself, the broken seat switch shuts tractor down.
…well that’s one possibility. There’s a few more.

 

[LD1]

I agree it sounds like a wiring/safety issue.

5 switches to look at
1. Seat
2. PTO
3. Neutral
4. Clutch
5. brake

And as it has been eluded to....they usually work in conjunction.

You say you bypassed the seat switch....how so? Just a jumper wire? Was it a 2-wire or a 3-wire switch.

Not sure on the deere, but on alot of compacts the seat switch is actually a 3 position switch. It senses operator presence, seat presence, and seat flipped up. The reason is for running something off the PTO that requires no operator....like a PTO generator, or a PTO log splitter. The MFG's realize it would be a PITA to have to have someone in the seat. SO you CAN actually have the PTO on and NOT be present on the seat of the tractor, but you must flip the seat forward immediatly upon getting off of it. Thus a 3-position switch....and 3 wires. So a simple jumper wire in there may be causing the hit or miss issues.

The clutch switch is usually only a starting thing....butt in seat, in neutral, and clutch pressed = start
The neutral switch is both a starting thing and off the seat thing. In conjunction with brake...and in neutral...with PTO off you should be able to get off the seat. So the seat switch and clutch switch are ignored if in neutral, brake on, PTO off
The brake switch is only looked at when getting off and tractor running. But may also need set for start
The PTO switch has to be off to start and you have to be on the seat. But doesnt really interact with the neutral, clutch, or brake switch


SO in one way or another all 5 switches interact with one another and either disable the start solenoid/relay, or cut the fuel off to kill the tractor (fuel solenoid).

Id start checking continuity of all 5 switches, both engaged and disengaged and see if that reveals anything

 

[Matt621]

Okay I am 99% sure I'm battling two issues.

Tried to start it today. Started from square one. Everything in neutral, PTO disengaged, hi/low in neutral. Would not start. Rowed thru the gears put it back on neutral, rechecked PTO, rechecked hi/low. Even cycled the throttle a few times. Turn the key and it started right up. Okay, so I let it idle for a few minutes... put it in gear and it did not die. Drove it around, worked fine. Okay so I'm going try and finish what I was doing yesterday. I worked about 40 minutes. All was fine. But I did not want to turn it off, so I jumped off it and to move some stuff out of the way. (I had bypassed the seat sensor). It was idling for about 10 minutes. Got back on it, and it drove fine, till I tried to pick up a bucket of stuff. Just low on power. Oh, "I'm still in high." So I shifted it to low and tried again.. then it died. But not like before. Before was instant. This time the idle slowly went down... and then tried to keep going and then died.

I tried to restart and it tried, but then could not keep going.

So, what this means is:

Idling for several minutes seems to have something to do it. It did the same thing yesterday when this happened.

And there is an issue with some switch because when it won't start it really won't. It's like a kill switch.

If I can get over that (just by luck it seems) it'll run fine till I let it idling for sometime. After that, it'll die like it's running out of air or fuel. I did check air filter. Dusty but by no means clogged. I'll replace it anyway. So there is likely a fuel filter someplace.

So now the question is: are their manuals for these things like Chilton and Edmunds for cars? I really need a shop manual to know where to look for filters, fuses, switches, wiring diagrams, etc.

Thanks

 

[Matt621]

Regarding the seat sensor. It's a 4 wire, all molded together. I took it apart. It has 3 positions:

1. no one on the seat, nothing is engaged. Open circuit.
2. someone on the seat. The two outside wires are shorted/connnected, closed circuit on the two outside wires.
3. Pull on the switch and the two inside wires are shorted/connected, closed circuit on the two inside wires.

#3. for for PTO operations.
#2. is for normal tractor operations.
#1 is for no one is on the tractor.

So I just twisted the 2 outside wires together and capped the two for the PTO since I'm not using it at this time.

 

[Matt621]

Thanks for the wiring diagram!!! Really helpful. First thing I did was go to the seat switch and what do I see? It goes to something called a "time delay control module." Great. What the heck is that? It goes to both the seat switch and the fuel relay. Anytime I read "timing" and "delay" and "control" all in the same sentence, I cringe.