1998 753F BOSS No Glow Plug Timer

[Oil Pig]

Years ago, I bought an old Bobcat 753 serial# 508612203 , and my brother joked that it looked like it had fallen off the back of a trailer on the way home. That winter, I decided to spruce it up and give it a little TLC. One issue stood out right away: the glow plugs didn't work. My solution? Park it in the heated garage and let my wife deal with frosty car windows. Over the years, this workaround has done the trick—keeping it warm makes it start right up. However, if I leave it outside on a cold night, it's a real struggle to get it going.

The machine has the BOSS system, but the glow plug timer never counts down. It just displays zeros and then switches to the hour meter. I've tested all the glow plugs with a multimeter, and they're good. However, there's no power to the busbar, likely because the countdown never initiates. I called the local Bobcat service department, and they suggested it might be the relay. I replaced it (there are only two near the starter that I could find) and swapped them around to test, but no luck. One of these relays also controls the starter, so I tried their advice, but the glow plug system still doesn't work.

I've considered adding a manual switch to power the busbar, but I'd prefer to fix it properly and have the timer work as intended.

Does anyone have advice on what else to check or troubleshoot to figure out why the countdown won't start?

Thanks in advance for any help!
Mike (long time listener, first time caller)

 

[Oil Pig]

Years ago, I bought an old Bobcat 753 serial# 508612203 , and my brother joked that it looked like it had fallen off the back of a trailer on the way home. That winter, I decided to spruce it up and give it a little TLC. One issue stood out right away: the glow plugs didn't work. My solution? Park it in the heated garage and let my wife deal with frosty car windows. Over the years, this workaround has done the trick—keeping it warm makes it start right up. However, if I leave it outside on a cold night, it's a real struggle to get it going.

The machine has the BOSS system, but the glow plug timer never counts down. It just displays zeros and then switches to the hour meter. I've tested all the glow plugs with a multimeter, and they're good. However, there's no power to the busbar, likely because the countdown never initiates. I called the local Bobcat service department, and they suggested it might be the relay. I replaced it (there are only two near the starter that I could find) and swapped them around to test, but no luck. One of these relays also controls the starter, so I tried their advice, but the glow plug system still doesn't work.

I've considered adding a manual switch to power the busbar, but I'd prefer to fix it properly and have the timer work as intended.

Does anyone have advice on what else to check or troubleshoot to figure out why the countdown won't start?

Thanks in advance for any help!
Mike (long time listener, first time caller)

???

 

[Oil Pig]

I ended up bypassing the Bobcat Boss system to warm the glowplugs. I used a Lawn Mower Starter Solenoid and a push button starter switch. Now, I'll jus manually heat the plugs and move on.

 

[foton]

I think you did the smart thing here,keeping it factory would have been nice but you could have chased that problem and I believe that it would have been expensive.

 

[Oil Pig]

I think you did the smart thing here,keeping it factory would have been nice but you could have chased that problem and I believe that it would have been expensive.

I had made it look factory as possible when I did it. I installed a red LED light right above the switch to energize the solenoid. I connected the hot wire for the LED to the output of the solenoid incase the solenoid ever stuck I would know to disconnect it.

 

[Lowe.Buuck]

Just a couple thoughts. The glow plug timer circuit operates based on Engine Coolant Temperature.

The BOSS display for Engine Coolant Temp shows one bar up to 190 degrees F. If the sensor is bad the BOSS should give you an ECxxx code.

However, you may want to check the resistance on the Engine Coolant Sensor. On the C-Series it is in the radiator and has a resistance of 970 ohms at 70 deg F and 1013 ohms at 80 deg F.

If the sensor is telling the BOSS the temp is above the Glow Plug on threshold temp, the BOSS controller would never power the glow plug relay.