Cat 320 almost back to life- Throttle Control problem

[Nolan]

Hello Friends,
I have read this forum for several years and enjoyed it thoroughly. Over the past year I have been resurrecting a Cat 320 serial number 2DL01890. The machine had been setting for more than a decade and was considered scrap when I started. It is a very used machine but will be an incredible asset at the farm where it will dig ponds and and be a great partner to an old Volvo loader that I am also working on.

The 320 now starts and runs smoothly at an idle speed. Turning the engine speed dial does show on the digital display as I turn it up and down but the engine speed stays at an idle. I have checked all the fuses I see in the fuse holder. I have confirmed that the solenoid on the throttle is moving freely and the engine responds by manually pulling on the throttle.

Can you help with suggestions on what I should check to continue to track down the problem?
Has anyone seen this in the past?

Second line of thinking, This is a very old machine that has very little computer control. if it is determined that the problem is in the computer, I won't be replacing it, instead I would be figuring out more direct rpm control either manual or a separate speed control. Has anyone else followed this path?

Thank you,
Nolan

 

[kshansen]

Nolan, first off I have no experience with a 320 but took a quick look on SIS and saw this that may be of interest.:
Backup System Components
The electronic control system is provided with pump backup switch (14) and governor backup switch (9). The switches function as a backup to the controller to prevent the machine from shutting down if a problem occurs in the controller.

Turning pump backup switch (14) to the TORTOISE position disconnects proportional reducing valve solenoid (15) from the controller. Solenoid (15) now is connected to battery positive and negative through a resistor. Connected like this, solenoid (15) will not change positions and the pump will operate continuously with a 15 to 25 percent lower output than the maximum (approximately equal to power mode II). When pump backup switch (14) is ON a signal is also sent to the controller.

Turning governor backup switch (9) to the MAN position disconnects governor actuator (13) from the controller. This overrides the engine speed dial switch and the controller allowing manual engine speed control by activating speed change switch (12).

Do you have any books on this machine? Like a service manual? If a wiring schematic would be of help let me know by "Start a conversation" and give me an email address to send it to.

 

[Jharp]

i would check the input at the solenoid when varying the throttle and see if the voltage changes.

 

[Nolan]

Thank you Jharp and Kshansen for the offer and suggestions.
I will be heading out this afternoon to start poking at it a little more. I will keep you posted.
The excavator is a Cat 320 serial number 2DL01890.

Best regards,
Nolan

 

[rmllarue91]

Definitely want to test powers and grounds but failure rate on stepper motor is huge. I think off-road equipment sells them aftermarket for $500 the things that kill them are exhaust leaks oil and or fuel dripping on them and sitting for periods of time...