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

[al3]

Never been under the hood of a 790, so consider that when you read the following.



The 790 schematic looks very similar to the one for 4100/4010/4110/4115. If indeed Yamnar used the same logic in the 790, then widen your search and look at the info posted on TBN for the same issue on those models. Lots of discussion about the function of the start and fuel relay switches, the safety integration module; how they work and suggestions what/how to check. Worth your time to find them, lots of good info. Things like how the fuel solenoid works, how to swap relays, how to ohm out the fuel solenoid, burned control boxes, etc. After you read some of them, the suggestions in the following 2 paragraphs will be easier to follow.

Consider the option of temporarily wiring in a pair of 12 volt lamp (bulbs, LEDs, whatever) in line with the safety modules output to the fuel solenoid. Run a long enough wire and put the bulbs where you can readily monitor them. The startup coil in the fuel solenoid should be energized for 5 to 10 seconds when starting—the bulb should be lit then go out. If you have a cranking but non starting engine and this bulb isn’t lit, you’ve narrowed down the problem.

The other wire running from the control module to the fuel solenoid should always be energized, and the bulb lit, as long as the ignition switch is on and the engine is running. It will provide a visual indicator if the voltage to the fuel solenoid is interrupted. i.e., if the tractor is running fine and the light goes out and the tractor dies, you’ll know something is amok with the safety switches or the control box itself. If the light stays lit and the tractor dies, then it’s time to look elsewhere. Again, lot of previous discussion on how to test resistance of the fuel solenoid itself, looking for faulty grounds, burnt control boxes.

Installing temporary wiring/bulbs is easier to do than pull the fuel solenoid on my tractor, as the two bolts securing the solenoid are tucked away behind some solid parts. It takes a long, skinny ¼ extension bar and a universal joint to get to mine. IMHO, if you don’t want to screw around with the lights, as previously suggested physically pulling the fuel solenoid is a straight forward option.



Good luck

 

[ROUSTABOUT]

If you bypass the kill solenoid on injector pump by taking it out, remove plunger, screw back in. That will get rid of the safety switches so you can get it in the shade. The wire can be un hooked and is energized in run. So a simple idiot light will do it. If light is on and shows good voltage, probably bad solenoid. You'll probably have to kill it by snuffing out air supply while solenoid is unaloosened.

 

[Wagtail]

With my seat switch, activated by my weight pressing down the 'cushioning' of the seat, I didn't bother jumping or even disabling the switch. I removed the entire assembly and tie-wrapped (zip-tied?) a piece of wood dowling across the switch's 'plunger' to keep it permanently depressed.

It now rests underneath my seat and has for the last 6 years. If I ever have to sell the 4105, I'll simply re-install the switch for the next owner.

 

[jthibodeau89]

As another post alluded, drain the fuel bowl and teplace the fuel filter.

 

[ssgp2]

My 990 did that around 600 hours also. Was the fuel shut off solenoid. On the time delay, it required both coils inside the solenoid to initialize, then only one to keep it engaged, but was sporadic. Before you hit Amazon or the dealer for said solenoid, check the electrical connection closely for loose or dirty connection. There are two different ones for your 790

https://partscatalog.deere.com/jdrc/sidebyside/equipment/67138/referrer/navigation/pgId/2622484

 

[RancherGuy]

... 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.

...

I've had my share of diagnosing tractor problems. Almost always, my issues narrow down to (1) sensors/switches, and (2) fuel.

When you talk about "not starting", there are two options: turning the key does nothing, or the engine cranks but will not fire up. When you describe, please clarify. The Doing Nothing activity is associated with sensors/switches. The Not Firing or the Slow Die you mention sounds like fuel. Here is what I suggest for diagnostics.

Remove the fuel filter. If it is empty, fuel is not getting from the tank to the filter, meaning fuel pump problem or line blockage before the filter. I just had such an incident last month with a pump that was intermittently failing. When it was activated (turned ignition switch to "on") and fuel line was free, sometimes it ran, sometimes not, sometimes when running it pumped and sometimes it wouldn't.

Once upon a time I found an elbow going into the filter was blocked with trash, like I forgot to replace the fuel cap once or twice.

If the fuel filter is full, then a good chance is that there is water in the filter or filter is stopped up.

Once I found that the pickup screen inside the tank was plugged, so even though pump and filter were good, they were starved for fuel. With this situation the engine was loosing power until it got to where it might not start, or would only start after sitting for a while.

 

[WCarlson]

Your problem may be a common problem on John Deere tractors: failed fuel shutoff diode. See the following for an excellent description and solution:

JD 2305 Fuel Shutoff Diode Bad

I have a JD 2305 that was running just fine, I shut it off for only a few minutes. It would not restart. It would run for just a second then die each time I would attempt to start it. After some initial troubleshooting and Google searches, I figured the problem to be the Fuel Shutoff...

www.tractorbynet.com

Bill

 

[greenmower]

Sounds like safety sensor. I pick up sticks and branches under and once in a while get one stuck near a safety sensor causing similar die downs. My biggest challenge was random cutting out under load. Would start and run fine with no load. It ended up being filings from a new fuel can dropped into bottom of tank and was randomly limiting fuel to the line. Had to remove fuel from tank and vacuum the filings out. Dirty fuel filter often causes same, enough fuel goes through to run without load, add load and fuel need isn't enough. Good luck finding.

 

[Garson]

As several folks have mentioned, it sounds like an intermittent switch with high resistance or a switch that's in marginal adjustment. Find every switch possible and saturate them with WD-40 and then actuate each switch a couple of dozen times to clean the switch contacts. You will likely find a switch that has a few ohms across it with the contacts closed. Switches should be less than half an ohm to function properly.

My neighbour had a John Deere hydrostatic drive and it would frequently stop moving just like the pedal was not pushed. It was the adjustment series for the hydrostatic drive so one couldn't push forward and reverse pedals simultaneously. There were 6 switches to prevent this. John Deere came twice to his property but it worked fine both times. They refused to do the adjustment series that required special tools and several hours to perform. He traded the tractor in on a Kioti and lived happily ever after.

Good luck.

 

[Gord Baker]

I hope you checked the Fuel level............. Sounds like a safety switch module somewhere...