Hey all, Heres what I'm working with. Everything was running fine until the machine wouldn't cut off using the key. Went around and shut it off with the fuel solenoid. Then the machine would not start. After some helpful advice, I pulled the starter and it was burn up and still in the engaged (extended) position. So replaced the starter and the machine fires right up, but I can hear the starter is still engaged and headed for another burn out. Cut the power for the machine and the starter quit whining and then shut the engine off via the fuel solenoid. So now if I cut the main power disconnect on, the machine tries to start up immediately. Even with the key switch disconnected. The machine will start and I can hear the starter still engaged. Thinking there may be an issue with the fuse box now, and plan to pull that tomorrow and open up to look for internal short. I have a wiring diagram for this machine thanks to a good fella here on this forum. Always have found the people here to be most helpful and know their stuff. Just curious if anyone has something to add and there is something else I am missing. :Banghead Praying for a fix so I can get back to work. Thanks!
Unhook the wire going to the s terminal on the starter and it shouldn't try to start. If it doesn't you need to find out what is sending power down that wire. Could be a relay, could be the ignition switch, etc. Just general info, I have no experience with that specific machine.
Second that. You described two or three problems that could both be caused by an ignition switch, that's a pretty logical place to start.
Think we found the issue. Ordered a new starter relay which is located in the fuse box. The relay appears to be sticking and continues to send 24V to the starter even after the ignition switch returns to the on position from the crank position. Ruled out the ignition switch sticking by removing the relay wire from the switch and testing the S wire on the starter. $75 and some change for the relay, plus the new starter. Looks like we might be back in business tomorrow after we pick up relay in the morning. I will post back tomorrow to confirm this fixed the problem. Thanks yall.
Be careful. Why wouldn't it turn off with the key the first time, how would the start relay do that?
Good Point. How would I further test the ingition switch? I had unhooked the starter relay wire from the ignition switch and the S wire still had 24V.
Ohm tested the ignition switch and appears ok. Could possibly be an intermittent problem? Because key did end of up working, just not right away. I have ordered an ignition switch as well as the start relay so I can get up and running tomorrow either way. Caterpillar said they can return parts as long as it has not been installed.
Possible there's a bypass from the starter circuit to pull in the fuel shutoff, as long as there's power to the solenoid, it may power the fuel shutoff also?
You have the electrical schematic. It shouldn't be too hard to figure out.
Lantraxco, Not sure I understand your questions?
You said in your first post that the engine wouldn't shut down with the key, I was wondering if there was a connection between the starter relay output or the starter solenoid and the fuel shutoff solenoid. Not common, but I have seen machines where the fuel shutoff solenoid pull in coil was powered by a connection to the starter solenoid. Thinking the stuck starter relay may have been sending power to the fuel solenoid also somehow? Might be an ECM issue Nige?
The fuel shutoff gets its power from the starter motor solenoid. When the starter motor solenoid pulls in it energizes wire #301 that feeds the fuel shutoff. The way the shutoff works is that when wire #301 Blue is powered it pulls the fuel shutoff from the "Stop" to the "Run" position. As soon as the keyswitch is moved from the "Start" position back to the "On" position wire #301 Blue is de-energized but the fuel shutoff stays in the "Run" position. To move the shutoff from the "Run" to the "Stop" position wire #326 Purple is energized when the keyswitch is moved into the "Off" position.
Thanks Nige. So when the starter relay stuck on, the starter solenoid was feeding constant power to the fuel shutoff?
Everything Nige said seems to be happening as its suppose to at the ignition switch. When I oHm the ignition switch out all connections correctly. The only odd thing I see is that when the switch is moved from the "run" to "stop position wire #326 is energized but only for a few seconds and then the oHm meter spikes. Reason I suspected the "start relay" is because wire #307 energizes when the ignition switch is moved to the "start" position but de-energizes when the switch is released back to the "run" position. Thought was the "start relay" is stuck because the contacts have corroded or rusted or heated together and are not releasing properly. How does the machine not shutting off fit in? I don't know.
I would say so. Has the stuck relay caused damage to the coil in the fuel shutoff because instead of simply being energized for a couple of seconds it's been permanently energized..? Who knows..? Anyhow ........ you can check it - there is a spec. There are actually 2 coils in the fuel shutoff. One should be 1.55 ohms, the other should be 10.3 ohms, both of those values +/- 10%. Obviously the ground wire is common for both coils. See below.
The more I learn the more things are making sense. Wire #200 to #326 ohms is 3.25 (solenoid in or out) wire #200 to #301 ohms is 0.0 (solenoid in) wire #200 to #301 ohms is 3.25 (solenoid out) wire #301 to #326 ohms is 3.25 (solenoid in or out) I think the fuel solenoid was permanently energized when we last ran the machine. When I tried to shut it off via the fuel solenoid when the key wouldn't work, there was clicking noise and resistance felt when I attempted to push the button. It would seem the solenoid was constantly energized into the "run" position.
And that's not how it should work. the "Run" side of the shutoff should only be energized for the same amount of time that the starter is actually cranking.
Parts came in on our truck this afternoon from Charlotte. Got the machine up and running shortly thereafter. Turns out it was the starter relay- Part 3E-7640-. And the fuel solenoid seems to be ok despite being energized for so long. Machine cranks, runs and then stops correctly with the ignition switch. Now I need to see if the good people at Carolina Cat will let me return the ignition switch I bought just in case it wasn't the starter relay. Had to also replace a breaker - Part 3T-2662- because when I was cleaning the corrosion off all the contacts in the fuse box the contacts on this breaker crumbled from rust. That was an extra $50 part. My guess is moisture inside the fuse box and corrosion of the relay contacts was the primary culprit. Let this one be a lesson to shed your equipment, if possible. Thanks to everyone who responded here.
Good job! :drinkup