John Deere 843L ii series

[Gabefost]

I have a 2019 JD feller buncher that has shut down on me. I was going to cut a tree and the rpm dropped down to 0 and the hydraulic light was blinking on my keypad. Since then it will not start. It turned over a few times and immediately died back down but it will not run. We've checked the red P66 wire that runs from the saw motor to underneath the cab and then to the engine. We've blown out and cleaned all the fuel lines and sensors to the fuel filters. And also changed the injector pump, but still no luck. Any suggestions on what to do next?

[Firewoodjoe]

Does it have jdlink? You'd think Deere could run the computer on something that new. 

[Gabefost]

It does, you would think you could get more info out of the computers. A few JD technicians ran the codes and came to the conclusion of an injector pump. This puts us back to square one

[newoodguy78]

Just a guess, does all the wiring and connections check out as they should? 
Did the technicians happen to say what the codes were? Maybe someone here would decipher them differently leading to the real problem. Bummer you had to replace the pump and still in the same situation. Best of luck with it.

[mike_belben]

Real sorry to hear of your frusteration. 

[Gabefost]

Just a guess, does all the wiring and connections check out as they should?
Did the technicians happen to say what the codes were? Maybe someone here would decipher them differently leading to the real problem. Bummer you had to replace the pump and still in the same situation. Best of luck with it.

We didn't see any damaged or loose wires. But if anything we may try changing the wire harness if it comes to it. The  only code that is showing currently is "low rail pressure fault". That's why we we're thinking fuel filters and injector pumps

[Firewoodjoe]

Has a mechanical guage been installed to be sure fuel pressure is actually lost? Could be a bad sensor or something causing all the shut down. 

[barbender]

A hung injector can cause a low rail pressure situation too, I think.

[Firewoodjoe]

I was thinking injectors too but figured that would have to be some pretty hung up injectors for it to not start. But if the computer is shutting it down maybe it don't take much. 

[kiko]

The dreaded low rail pressure.  This can be one if the hardest codes to diagnose because the fault could be anywhere between the fuel tank and the injectors.
-- Stopped up supply, make sure to check any 90
   fitting where the fuel hoses enter the fuel filter
      head.
-- High pressure common rail pump( already
     eliminated.
--  Rail pressure relief valve.  Find the return line
      for the rail relief and remove.  Absolutely no
      fuel should be coming past this relief when
      starting, not even a drop.
-- Injector or quill leaking.  Again find the return
     line from the injectors and remove, no fuel
     should be coming from injectors when starting.
     If there is a flow , plug off each Injector one at a
     time until the flow stops. 

[mike_belben]

Good stuff kiko

[kiko]

https://youtu.be/3SNbXyMRRrg?si=LtTMyMwn3wBbaYZ9


In this video the rail relief is leaking enough to just sweat the fuel out.  With extended crank time this engine would start, but would not run at full horsepower because it would not build enough rail pressure to meet the psi that was demanded by the ecu. Replacing the rail relief fixed that engine.

[kiko]

https://youtube.com/shorts/zfdDUwrC8KE?si=cXutlEpmyhNr8eUl


This a QSB 6.7 Cummins but common rail theory is same across the board. Make sure the TUBES are tight!!  Also, those john deere lines will often leak once you take them off and reinstall. John Deere claims them to be single use. That is me by the way,  now yall know what I look like when I show up at the pig cooking one day!

[Wlmedley]

Fuel rail pressure sensor could also be malfunctioning. May need to get someone to plug into machine with computer so pressure can be monitored while cranking. Don't recommend trying with your own gauge. Pressure is extremely high, probably over 25000 psi. I have found bad connection at rail sensor will cause problem. No use throwing parts at it, newer machines are pretty hard to troubleshoot without proper equipment.