Hitachi EX120 wont shut down.... the wires to the control stay energized

[centerline]

I am working on an EX120 that has the stepping motor to control the fuel pump, but when we shut the switch off the stepping motor does not lose power, so the machine stays running.
when we shut it down with the manual cable, then the stepping motor loses power after the alternator stops producing.
the machine starts and runs fine.

is there a relay or diode that has failed and is causing the stepping motor wires to remain charged when the ignition is turned off?... and if so, where would I find it?.... Thank you

 

[catfixer]

not too familiar with the hitachi, but usually there is a relay that pulls the fuel linkage shut and holds for 20 or 30 seconds. should be fairly close to the stepping motor if you just follow the wires coming off of it.

 

[garyw]

I am working on an EX120 that has the stepping motor to control the fuel pump, but when we shut the switch off the stepping motor does not lose power, so the machine stays running.
when we shut it down with the manual cable, then the stepping motor loses power after the alternator stops producing.
the machine starts and runs fine.

is there a relay or diode that has failed and is causing the stepping motor wires to remain charged when the ignition is turned off?... and if so, where would I find it?.... Thank you

What's the model, is it a EX120-2 or -3 or -5?

 

[centerline]

its a EX120-5...
the stepping motor IS the throttle and shutdown control relay.... there are 4 electrical wires that go to it. when the igniotion switch is shut off, the power remains at the wires.
when it is then shut down manually and the alternator stop producing, the power goes away at the wires going into the stepping motor...

if the engine is NOT running, the stepping motor cycles normally as it is supposed to.... we had a new motor connected to the wire harness to confirm this, while the engine was running and while it was stopped and just cycling the ignition switch....

 

[garyw]

Does the engine operate as normal? Is the engine revs high enough when at full RPM? Does the auto idle, all the modes work ok? Have you performed engine learning? The way the system works is the 4 pin plug as 2 v+ wires and 2 V- wires all the time. The 3 pin plug is the EC sensor. It tells the controller what position the motor is in. Depending on what revs you demand, the controller sends a current down the 4 pin plugs to turn the motor back and forth. At low idle, the controller should be expecting to see a 2.5V reading from the EC sensor( from the centre wire of the 3 pin plug) If not the controller may be confused and not work properly. Make sure all the throttle cable and linkages are good or the engine learning may fail. There's a switch next to the fuse box and diagnostic port. It should always be in the centre position. The cover of the switch has an E on it. With the ign off,move the switch in the direction of the E, put the ign on for 15 seconds, turn ign off. Wait 15 seconds. Put the switch back to the centre and then start the engine and test. If it now works ok then great. If it doesn't start, idles too high or too low you may need to set the idle speed. You'll probably need MPDr to do this accurately. If its not done accurately the again, if the target engine speed isn't close to the actual speed the the controller gets confused. Let me know how you get on.

 

[centerline]

Does the engine operate as normal? Is the engine revs high enough when at full RPM? Does the auto idle, all the modes work ok? Have you performed engine learning? The way the system works is the 4 pin plug as 2 v+ wires and 2 V- wires all the time. The 3 pin plug is the EC sensor. It tells the controller what position the motor is in. Depending on what revs you demand, the controller sends a current down the 4 pin plugs to turn the motor back and forth. At low idle, the controller should be expecting to see a 2.5V reading from the EC sensor( from the centre wire of the 3 pin plug) If not the controller may be confused and not work properly. Make sure all the throttle cable and linkages are good or the engine learning may fail. There's a switch next to the fuse box and diagnostic port. It should always be in the centre position. The cover of the switch has an E on it. With the ign off,move the switch in the direction of the E, put the ign on for 15 seconds, turn ign off. Wait 15 seconds. Put the switch back to the centre and then start the engine and test. If it now works ok then great. If it doesn't start, idles too high or too low you may need to set the idle speed. You'll probably need MPDr to do this accurately. If its not done accurately the again, if the target engine speed isn't close to the actual speed the the controller gets confused. Let me know how you get on.

the engine runs great without any noticable problems... it idles fine, the high rpm is good and not over rev'ing, the power is good and the throttle ramp knob works as it should, but it just wont lose 12v power at the stepping motor (to allow it to shut down) when the keyswitch is shut off.

but we will try the "learning" procedure to see if it helps, thank you..

 

[garyw]

the engine runs great without any noticable problems... it idles fine, the high rpm is good and not over rev'ing, the power is good and the throttle ramp knob works as it should, but it just wont lose 12v power at the stepping motor (to allow it to shut down) when the keyswitch is shut off.

but we will try the "learning" procedure to see if it helps, thank you..

The EC motor won't lose voltage as such with the key off. Basically the controller knows the EC reading is 2.5 volts at idle speed. The engine learning procedure will pull the throttle cable fully closed and then fully open and the controller remember those voltages. For example, the EC voltage may be 2volts fully closed and 3.3volts fully open with a 2.5 volt reading at idle. When you go to full RPM the controller sends a signal down 1 of the 4 wires to achieve the 3.3volts then it knows its at full rpm. Then when you key off it will send a signal down the other wire to turn the motor in the opposite direction till it reaches 2 volts, then it knows the engine should shut down at that. That's why the engine learning procedure and the idle speed is vital. Because if the controller see's voltages and rpm's it doesn't expect it throws up faults. Also, i'm almost certain the EC motor switches with GND. So the 24 volts is there all the time, and the controller sends a GND down to whichever wire to turn in that direction. I'm almost sure engine learning and setting the idle speed will sort out your problems. Unless there's an issue with the controller. Hope this helps and you get it sorted.

 

[excavator]

This past winter I had a Zaxis 230 that did the exact same thing. After many hours of chasing multiple ideas I found that there had been a small fire down behind the batteries and had melted 8 or 9 wires together with the battery positive cable. This kept the battery relay energized even with the key off so the shut down circuit also remained energized. The amazing thing is that it everything else worked just fine, it blew no fuses and fortunately not the computer.