753 locking up and stopping

[Mlewis]

Just wanted to update it's been several months now and machine is running great so it's safe to say it was the BICS controller which is the black box if your sitting in the seat it would be to the right side behind you it tells you if the lap bar is down and several other it seems to be the brains of my machine lololo

 

[daytona701]

Still locking up and stopping. Since last post changed the seat bar position sensor and that didn't work. Called local Bobcat dealer that sold the machine and did some service work before. Service manager said brake switch on overhead console or rpm sensor at flywheel could be the cause. I unplugged brake switch but now I need to figure out how to test the rpm sensor. Any ideas? Thanks.

 

[daytona701]

Using 753 Bobcat yesterday parking brake kept engaging while operating. Unplugged brake switch and checked flywheel rpm sensor. Sensor face was in contact with flywheel. Removed sensor and bench grindered face to have air gap between sensor and flywheel. Reinstalled sensor but parking brake kept engaging. Does anyone know how to test rpm sensor? Also overhead beeps 3 times at key on.

 

[reaperman]

I would start by disengaging the parking brake locking pin manually. Its located between your legs as you're sitting in the machine. Naturally you need to lift the cab and find the solenoid that controls the pins up and down motion. If the rpm sensor is failing you, the glow plug countdown timer will continue to countdown repeatedly.

 

[daytona701]

Turn key to on position, get three beeps and glow plug timer starts countdown. When countdown is complete press light switch for two seconds to retrieve code. No codes on display but glow plug timer starts again. Start machine and oil light is on even though recent oil/filter Chang. Manual oil pressure gauge reads 60 psi at idle. Still have parking brake engagement when working machine. Seems to get worse as machine warms up.

 

[daytona701]

Bought the factory service manual. Could oil light could be high oil pressure? Manual says could be too high viscosity or pressure relief stuck closed. Changed oil/filter using Shell Rotella 15w40. While oil filter was off checked pressure relief valve and ball moved easily against spring. Machine has about 1050 hrs. Currently have oil pressure sensor unplugged with manual gauge installed. Oil pressure at idle shows 60psi going up to 70psi at half throttle. Parking brake engages by itself while machine is working. Battery terminals are clean and tight with 12.6 volts at rest and about 14.5 engine on. Changed alternator and belt last week. Checked wire harness for break in insulatio. Could common ground to oil sensor circuit and parking brake solenoid be causing the two problems?

 

[cdmccul]

I don't know the name of the box, but is there a box behind the seat with a couple LEDs on it? We had one at work do this. I didn't get to interact with diagnosis, but the solution was to replace that box.

 

[daytona701]

Replaced the rpm sensor, removed manual oil pressure gauge and reconnected oil pressure sensor. Took machine out to work and problems returned. Parking brake engages while working and oil light comes on. Put machine back in shop and started going over factory service manual. Checked belt tension on newly installed alternator and it was slightly loose. Adjusted belt and started engine. Voltage was jumping around 12.5 to 18 and not consistent. Shut down and inspected wiring and all looks good. Machine has about 1050 hrs. Got second voltage meter, started machine and at half throttle battery voltage now at 12.5 solid and alternator not charging. Also changed all light bulbs front and back and lights won't turn on. Wondering if I have a computer problem.

 

[billyb]

Replaced the rpm sensor, removed manual oil pressure gauge and reconnected oil pressure sensor. Took machine out to work and problems returned. Parking brake engages while working and oil light comes on. Put machine back in shop and started going over factory service manual. Checked belt tension on newly installed alternator and it was slightly loose. Adjusted belt and started engine. Voltage was jumping around 12.5 to 18 and not consistent. Shut down and inspected wiring and all looks good. Machine has about 1050 hrs. Got second voltage meter, started machine and at half throttle battery voltage now at 12.5 solid and alternator not charging. Also changed all light bulbs front and back and lights won't turn on. Wondering if I have a computer problem.

Just a thought! I know from experience that if you are not charging and voltage drops near 11 while working the park brake will engage

 

[daytona701]

That's what I'm thinking too. Rebuilt alternator from Autozone. Showed about 14.5 volts after installation. Does the computer control alternator output? I'm getting the oil pressure light and the front and rear lights aren't working. Also no codes when pushing the light switch but the glow plug starts countdown again. Factory service manual says to check all grounds when multiple electric problems present. I haven't seen a diagram showing where all the grounds are. I replaced all light bulbs and all fuses and relays and cleaned the sockets. Engine and hydraulics are strong. I could pull the parking brake solenoid/pin but I don't want to lose the safety factor.

 

[brdgbldr]

The computer does not control alternator output. It has to be higher than 12 volts or the battery won't charge. I have gotten bad rebuilt alternators in the past.

I would hook up a voltage meter to the alternator that I could monitor from the cab. Maybe also on the battery. At least this might eliminate those two.

An intermittent short could cause a problem like this also. They are the biggest headache ever. Dealers will just start replacing wire harnesses.

I'm sure you've already looked, but a small rub through that is grounding out could do this. Also, a pin in a wire connector that is loose, dirty or bent can also do this.

Since you are having issues with electrical that is all switched from the cab I would go over the wiring and switches in the cab with a fine toothed comb. Hopefully it's not your your left side panel going bad.

I had a blade connection in one machine that was loose. It was causing all sorts of problems but it was intermittent so I couldn't find it. After I started pulling all the connectors, one at a time, I found the loose one, crimped it tight, and the problems went away.


Good luck

 

[cdmccul]

There's got to be a voltage regulator. If the alternator tests good, then the voltage regulator is to blame. If the regulator isn't a part you can see, then the computer is what is regulating.

You'd have to monitor the field energizing voltage to the alternator.

 

[daytona701]

Ok, the factory manual has the procedure for testing the alternator. Monitoring the the field energizing voltage sounds good. What field energizing voltage is within specifications? I've looked at the cab wiring but will check again. Is there a diagram showing where the grounds are? It's a 753G.

 

[cdmccul]

I edited a spelling error in my post above. Let me do some digging here.

 

[cdmccul]

I don't see what serial number you have, so I'm not sure which parts catalog to study.

But I do see that even if "internally regulated" it still has 3 wires going to it. So that's one end of the field, the other end of the field, and the main power cable.

The field is controlled by a voltage regulator some where. Sometimes it is a small metal box the size of a pack of smokes, but more and more often on newer and newer stuff, that voltage regulating is done by the computer.

I don't know what Bobcat calls for though.

As I'm doing some digging, I see there may be alternate answers than what I'm providing... Hopefully what I add is of use.

 

[daytona701]

It is my understanding that modern alternators are internally regulated. The machine uses the 90amp alternator with the red positive attached to the output terminal, a black ground attached to the alternator frame and a 2 wire plug which is the exciter for the field. Where does the exciter voltage come from and how is it regulated? So what I understand is output voltage is determined inside the alternator by the internal regulator and exciter voltage is determined by some dark force in the universe called a computer. Is this correct?

 

[daytona701]

Today I removed both positive and negative cables from the battery and charged the battery with a trickle charger for 4 hours. Cleaned and wire brushed the terminals. Built up the positive terminal with rosin core solder and replaced the negative terminal. Battery voltage at rest was 12.58 volts. Double checked alternator connections and all were tight. Reinstalled battery and both cables and started machine and tested voltage and got 12.48. So have to assume got a bad rebuilt alternator. Alternator is a Duralast from Autozone. Wasn't a stock item and took 3 working days to get in to the store. Will cross reference in the morning to see if an alternator is available locally. I'm in south Mississippi. Still have to check cab wiring and cab control panels. Pulled the cab control panels last week and cleaned mud dobber nest. Will report back after alternator is replaced again.

 

[cdmccul]

I can not find a source for what the field current should go between. You can "full field" the alternator and your output voltage can reach 120ish volts.... And if the battery is already at 13-14 volts, the field will be at 0 th not try to overcharge the battery.

Have AutoZone bench test the alternator. Then have another shop test it.

If both say its good, then it's probably good.

You can wire up an independent regulator to make it charge... But I don't know what the computer will think of that. In the automotive world, it would trip the alternator light on the dash, and maybe trip the "check engine" light.

No idea what the bobcat computer would think.

 

[daytona701]

Is there a fusible link between the battery and alternator field voltage or is it fused?

 

[daytona701]

Factory service manual schematic is 25 amp blade fuse for alternator field circuit.