S 650 Bobcat blown 100 amp fuse

[3rdgendslmech]

I rode out to work on a friends bobcat that wouldn't start after he had shut it down to talk to an inspector. From what he tells me everything was working fine and was running fine then when he got back in it the nothing would turn on when he turned the switch to the "on" position.
It only took me a couple minutes to figure out the main fuse to the panel had blown but at this point I'm stumped on why it blew. I connected the 2 wires together to get in on a trailer and back to his yard and started to diagnose what happened. I put in a smaller CAT 80 amp resettable breaker started the machine a dozen times nothing. Then I turned all the lights on, turned the A/C on and turned the fan to high and still couldn't get the breaker to trip. It threw a code M3128 which is an interrupted power failure.
Alternator is charging at 14.1 volts. The hot wire after the fuse going to the fuse panel looked and I OHM checked it and got no resistance to ground. The main ground clamp looks a little suspect, where the bolt goes through the ground clamp on the battery is cracked and noticed it wasnt very snug on the negative post. I've never seen a machine blow a main fuse due to loss of ground but I ain't seen it all yet either. Only other thing I was thinking of doing was taking the starter off and sending it out to be rebuilt or just buy a new one.

 

[mountainlake]

Could have just been a bad fuse, I'd run it until it does it again. A starter takes way more than 100 amps, just the solenoid circuit would be running through the fuse. Steve

 

[phil314]

I was also going to say it could just have been the fuse. They heat cycle and vibrate, they can just blow.

I've had it happen to me. I had a main fuse blow once. Could find nothing wrong. Put a new one in and never had another problem with it.

 

[crewchief888]

Only time I ever saw a blown 100A fuse was when a glow plug was dead shorted.

 

[3rdgendslmech]

But even at that wouldn't it have blown the glow plug fuse or burned out the relay before it went all the way back to the main fuse?
I know on older cat equipment if a glow plug wire shorted out in the harness or if a plug dead shorted it would kill the magnetic solenoid or blow the fuse.

Only time I ever saw a blown 100A fuse was when a glow plug was dead shorted.

Anyhow for what its worth....rode back down there last night after work still started up just fine, too warm for the glow plugs to turn on but ohm'd the harness and each individual plug and they all measured pretty close to eachother.

On a unrelated issue same machine....what's the hyd relief pressure set at on these machines. 3500 psi?
I tapped a guage into the quick connect port of the control valve and was getting 2000-2300 psi. Owner is complaining that the hyd breaker and loader seem a little weak. Going to try to adjust the main relief sat morning and tap a flow meter in to see if the pump is still flowing okay

 

[mountainlake]

New
But even at that wouldn't it have blown the glow plug fuse or burned out the relay before it went all the way back to the main fuse?

Most likely and that's why it could have been a bad fuse. Steve

 

[crewchief888]

Only time I ever saw a blown 100A fuse was when a glow plug was dead shorted.

the ONLY time in the past 20 years, ive seen the 100A fuse on a bobcat blow was when 1 of the glow plugs had a dead short..

typical hyd relief pressure is anywhere between 3300 and 3500 PSI, and you should see somewhere around 18-20 GPM free flow and 130F-140F oil temp.

 

[3rdgendslmech]

I'm convinced now that it might have just blown the fuse too!
Started adjusting the main relief valve.....1 1/2 turns in got me up to 3500 psi but it doesn't consistently peg out at 3500. There's either a piece of trash holding it open or it's got a blown seal. Sometimes even after I adjusted it it wouldn't get past 2100. Ordering new valve Monday morning.

 

[Burnin]

X2 on main fuse blown from glow plug circuit... G series machine had the glow plug wire rubbed through on the block.
With the machine powered up you could try gently tugging and pushing the wiring harness to see if it kicks the fuse.... sometimes a wire can rub on the backside of the harness where it can't be easily seen... but fuses can just go from time to time as well...