Cat 312 throttle failure

[dirtdobber1]

Hello all. I have a Cat 312 B L with about 3,000 hours. The machine has been sitting idle for a month or two. I just repaired a hydraulic leak and started the machine to discover that the electronic engine speed control will not bring it above idle. There are two pieces of history that are important.

First, and most importantly, while the machine was idle some rodents chewed on the wiring harness. I have repaired the obvious damage, but mice can get into more places than I. I recognize damaged wiring is the most probable cause of my troubles.

Second, the hydraulic leak completely drained the system. While the machine was down, I switched off the main power supply at the electrical panel behind the cab (to keep some dummy from trying to operate it).

To give you some symptoms, the engine speed control knob and the digital display are communicating. As the knob is turned, the numerical readout changes accordingly. The controller (located in the same compartment as the hydraulic pump) is functional because it works enough to allow the engine to start and idle (it has to move the rack on the injection pump to start). The cableling from the controller to the injection pump is fine.

In light of the fact I likely have a wire chewed up somwhere, I guess my question is this: Since the hydraulics were drained and the main electrical shut off, is there anything that has to be reset for all to function properly?

Thanks in advance for your thoughts.

 

[PAcattech]

good Morning dirtdobber1,
there would be nothing to reset Id think your right on with chewed wire, Did you try the throttle back up switch? its in the back of the right armrest there are two switches flip the one into manual and the other is a momentary switch that when held sends voltage directly to the govenor acuator bypasses all electronics. 312 is a mechanical engine the only thing that is controlled with electronics is the throttle. The controller in the pump compartment has nothing to do with the engine starting or idling.

 

[Nige]

If you want to start tracing wires post up the Serial Number prefix of your machine and I can find the wiring schematic for it fairly easily.

 

[dirtdobber1]

Thank you. The serial number is 8jr0124.

 

[dirtdobber1]

Let me try again. The serial number is 8jr01214. Sorry.

 

[CRAFT]

Hmmmm ! ....just a thought to check but ? .... I have replaced my throttle control motor at about the same hrs as yours, can't remember the sequence to check but either way could tell you if it is possibley there ........ I did this check with the throttle cables removed from the fuel pump ...... with the machine running stand by the hyd pump door (rt/rear door) put your hand on the actuator, have someone in the cab changing the speed control knob, and listen/feel if the motor tries to shift ..... the part I can't remember if the same test will work with the engine off and key on only ...... the reason i'm thinking this is you posted that the machine sat for quite a while .....my throttle cables were totally seized in the sleaves due to wear and heat from the engine and where it goes past the muffler, the sleaves were melted inside, just enough to prevent the cables from push/pulling ........ I know you posted about the chewed wires, but you spliced them back ....... like I said just a thought

Give it a try you've got nutt'n to loose .............. Good-luck .........GK

 

[dirtdobber1]

Here's where I am on this problem. The gov control motor/unit works, because I can rev up the engine with it in bypass/manual mode. Based on tracing all the wires, it looks like the "feedback" wire is the signal from the computer to the gov control. I can measure voltage (with key on, engine not running) in the feedback wire at a little over 4 volts, regardless of the setting of the throttle dial - voltage doesn't change. I know the computer is getting the signal from the throttle dial because the digital readout functions with the dial (its signal comes from the computer). Does anyone know:

Does the computer have to have signals from other sensors before it will operate the gov controller?

Thanks and Happy New Year

 

[heymccall]

Water damage (**** poor design) with the auxiliary hydraulic controller module can cause that. Is the machine equipped with auxiliary hydraulics? ( the system in question has a LED numeric display with four soft touch buttons, usually mounted by the air cleaner, underhood )?

 

[dirtdobber1]

I don't believe it has auxiliary hydraulics, at least it doesn't have any extra connections for anything I have noticed. Thanks for the info, but luckily over the weekend I found the problem and all is now well.

The problem was one circuit that had been damaged, which ran from the throttle override switch in the armrest to the computer. Repaired the wire and everything runs fine.

Thanks to everyone for the input.