[AT] Not quite an antiques problem...

[John Maddock]

....but a puzzle for the brains trust, never the less!


JCB JZ140 excavator, (9500 hrs) electrical problem.
Briefly:  machine has not been used for most of the winter, but I’ve 
topped up the batteries twice each month.  Noted at the last charging 
session a week ago that  one of the batteries took a long time to reach 
full charge.
Today, the electronic monitor screen showed low battery voltage & the 
starter motor refused to operate.
Connected 24v from external batteries & everything sprang to life as 
normal.
Moved the machine maybe 5.0 m to lift and reposition some equipment, 
then moved it 5.0m back again, the engine running for maybe 15 mins.  
Aircon was on at the same time to wet the compressor seals.  Decided to 
check the battery state, so killed the engine and re-started it - just.  
Tried again, and the screen showed low battery voltage and flywheel 
sensor fault.
Reconnected the jumper batteries - and observed the following:
1. “Dead” electronic monitor unit; no screen, no symbols.
2. A very dim LED on the Emergency Stop button. (Usually, that has to be 
used as well as the switch to stop the engine. No idea why; been that 
way since I bought the machine).  In addition, pressing the button did 
not switch off the dim LED, as it normally would.
3. The engine starts - and stops instantly.
4. The throttle arm does not move; it is unclear if it remains in the 
“engine stop” position and as a result the engine is somehow running 
briefly on residual fuel.  The run/instant stop is repeatable, not a 
oncer.
5. Switching to “limp mode” makes no difference to any of the above.
I’ve:
1  checked the fuse for ECU-STD, EMS Battery Supply; multimeter said its 
ok.
2 disconnected the onboard batteries; now running completely on fully 
charged, external, jumpered batteries.
3 Read the service manual carefully.  It suggests checking input/output 
voltages at several input/output points on the ECU.
Considering Farmer's frequent calls "Check the grounds, check the 
grounds" does this sound like an earthing fault at a point common to all 
the observed irregularities?


JV
 
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