I have a hitachi in the shop with a very inconsistent throttle control. The machine came into the shop for an engine replacement. Upon arrival we noticed that we had no throttle control. We dropped a new engine in and all is well that way. When we were ready to fire the machine for the first time we had it start and go right up to full throttle.. We were unable to idle it back, and also unable to shut the machine down with the key. We have no control over the stepper motor from the cab. When the key switch is turned to the off position, the stepper motor destrokes the injection pump, but after a few seconds strokes it back into full fuel. This doesn't happen every time tho. Sometimes it seems to stay at the idle position like I would think it should. When we turn the key on and rotate the dial, the control arm on the motor moves around a bit, but its very irratic / inconsistent. Sometimes it seems to work ok, than other times nothing at all. We have the low idle screw turned all the way out, and the machine still fails to power down with the key. I have checked the resistance of both coils on the stepper motor and have 5.4OHMS on both which seems ok. If I backprobe the connectors to the motor im only seeming 3.5v @ both coils. The computer have supposedly been replaced by another dealer, with no results (cannot verify this). Also the potentiometer within the stepper moto is reading 2.7v @ its idle position. Does anyone have any helpful tips, Or even better A WIRING SCHEMATIC!!??? Anything will help, thanks PS : already tired the learning mode procedure
Is the throttle cable and ball joints ok? Have you tried setting the engine speeds as well as engine learning? And if the engine learning has been performed correctly the voltage of the EC sensor( potentiometer) should be as close to 2.5v as possible. I'll copy and paste some brief info from the manual. Also a snap shot of the wiring diagram. ENGINE SPEED ADJUSTMENT AND ENGINE LEARNING After removing and/or replacing the components as described below for repair and/or inspection, or if error in engine speed is found, readjust engine speed and perform engine learning. • Removal of the engine, engine control cable, or EC motor • Replacement of MC Adjustment of Engine Speed: 1. Turn the key switch to the START position to start the engine. NOTE: Turn the air conditioner OFF. 2. Rotate the engine control dial to the minimum speed position. (The output voltage from the EC sensor is 2.5 V.) 3. Deactivate the auto warming up and ECO control systems by Dr. ZX. 4. When Dr. ZX is not available, keep the engine running for about 15 minutes to warm coolant temperature to more than 30 °C (86 F°) until the auto warming up control system is deactivated. 5. Loosen the bolt holding the control lever to the EC motor output shaft. 6. While monitoring the actual engine speed with Dr. ZX or the engine speed meter, adjust the control lever so that the minimum speed (slow idle) matches the specification. Specification: Refer to T4-2 OPERATIONAL PER FORMANCE TEST. 7. Tighten the lever holding bolt to secure the control lever to the motor output shaft. : 13 N⋅m (1.3 kgf⋅m, 9.4 lbf⋅ft) NOTE: Don’t lubricate the motor output shaft. Engine Learning: 1. Turn the key switch OFF NOTE: In case the engine doesn’t stop when the key switch is turned OFF, pull the handle located under the seat to stop the engine. 2. Disconnect Dr. ZX. Wait for 5 seconds. 3. Turn the learning switch ON. 4. Turn the key switch ON. Wait for 5 seconds. 5. Turn the key switch OFF. Wait for 5 seconds. 6. Turn the learning switch OFF. 7. Check the engine speed.
The slow idle speed is 950 + or - 100
try to replace the throttle motor assembly usually its the problem. also try to remove the throttle angle sensor.
We have a brand new throttle motor on it right now. I try following the learning procedure and it doesn't do much. As soon as I KEY ON I can hear the throttle motor adjust. Im under the impression that upon KEY on (and speed dial turn all the way down) I should see 2.5V @ the signal wire for the sensor. As soon as I key on in low, the motor adjusts to 4.97 volts, and as I dial the throttle up it increases to 5.0V than drops right off to 0.0v. That schematic would be amazing to have, but when I zoom in on it it goes too blurry to read. Can someone email it to me?? [email protected] Thanks
Thanks for the diagram. is there any way I could get a better picture. Soon as I zoom its too pixelated to read
What's the value from the throttle dial when it's low idle? It should read around 0.4v i think. You can read that through the monitor. If your not sure how to do it let me know and i'll email the procedure. It sounds like your stepper motor is way out to begin with. If its at 4.97v and you turn the dial up then when it reaches 5 it'll go out of range. Try and get the 4.97v down before the engine learning. Maybe try and power it up without the linkage on it. Keep the voltmeter on it and if it gets near the 2.5v unplug the 4 pin plug so it stops moving. Turn ign off, refit the linkage and plug it back in then go through the engine learning process again. I sent an email with the diagram