I want to install an RPM tach in my 863 non BOSS, help pls

[kilohertz]

Hi guys, I want to put a tachometer in my F-series 863, non BOSS, old fashioned 3 gauges type overhead console. I see the RPM tach sensor on the bell housing, and the 2 wire plug and wires going off into the engine harness....where do these wires go and is the sensor actually used without a BOSS computer? Possible they run right up to the cab gauge pod but aren't connected? I have the service manual but the diagrams aren't really clear in identifying where the wires go. I also have a tach which will work with a distributorless engine so I am hoping this will work. Any help would be appreciated. Cheers

 

[Tazza]

The issue might be matching the sensor with the tach you plan on using. There will be ones you can get that mount to a fuel injector line and it detects the fuel pulse to measure the engine speed.

 

[kilohertz]

The issue might be matching the sensor with the tach you plan on using. There will be ones you can get that mount to a fuel injector line and it detects the fuel pulse to measure the engine speed.

Hi Tazza, Ya I hear ya, the tach I have works with pretty well all ignition type systems, points or hall sensors, and since this is a hall effect, or at least some form or magnetic pulse pickup, should work with the tach. I pulled off the gauge pod today, no red/blu wire in there, I'll try to find a wiring diagram for this again tonight. I may just poke a pin into the wires coming from the sensor and see if it works just sitting in the engine bay, then run a wire to the cab if it does. It's a generic tach, big box auto store, if there is no connection to the sensor, then I will figure out what it needs. I would still like to know if this sensor is used in a non BOSS Bobcat, and if so, what is it's function? Cheers

 

[Tazza]

Hi Tazza, Ya I hear ya, the tach I have works with pretty well all ignition type systems, points or hall sensors, and since this is a hall effect, or at least some form or magnetic pulse pickup, should work with the tach. I pulled off the gauge pod today, no red/blu wire in there, I'll try to find a wiring diagram for this again tonight. I may just poke a pin into the wires coming from the sensor and see if it works just sitting in the engine bay, then run a wire to the cab if it does. It's a generic tach, big box auto store, if there is no connection to the sensor, then I will figure out what it needs. I would still like to know if this sensor is used in a non BOSS Bobcat, and if so, what is it's function? Cheers

I see no reason why it would be needed in a non G or boss series machine either. In the newer machines, the computer can see the engine speed and if there is no charge pressure, it shuts down to try and save the pump.
Does your machine have a digital display on the left side? Or does it have round gauges?
Round gauges, i wonder if someone installed a different engine/bell housing that had the sensor that isn't used.

 

[kilohertz]

I see no reason why it would be needed in a non G or boss series machine either. In the newer machines, the computer can see the engine speed and if there is no charge pressure, it shuts down to try and save the pump.
Does your machine have a digital display on the left side? Or does it have round gauges?
Round gauges, i wonder if someone installed a different engine/bell housing that had the sensor that isn't used.

I want the tach so I can see what RPM I am operating, nothing to do with safety or shut down, I simply want to know. I tried connecting to the sensor wire today and the tach didn't register. I found some schematics that I can read and the RPM sensor on the bell housing goes to the BICS box, to let it know it's "okay to go". BICS won't arm without the sensor signal, so it's factory original. I have round gauges in the right pod, Fuel, water and Voltage, again all original. I'll try making a little transistor or ?? amplifier or buffer and if that doesn't work, I'll investigate the fuel injector pulse thingy. Cheers

 

[Tazza]

I want the tach so I can see what RPM I am operating, nothing to do with safety or shut down, I simply want to know. I tried connecting to the sensor wire today and the tach didn't register. I found some schematics that I can read and the RPM sensor on the bell housing goes to the BICS box, to let it know it's "okay to go". BICS won't arm without the sensor signal, so it's factory original. I have round gauges in the right pod, Fuel, water and Voltage, again all original. I'll try making a little transistor or ?? amplifier or buffer and if that doesn't work, I'll investigate the fuel injector pulse thingy. Cheers

The sensor should be 3 wires? i assume you will need to apply power from your universal gauge to the sensor to get a digital output from it. Or that is how the sensors i have seen work.
Another option is to add a different style sensor in place or in addition to the one that is there?
I'd also check that the fly sheel does indeed have a magnet for the pickup signal. I have never looked closely to confirm there is a magnet in there, i just always just assumed.

 

[kilohertz]

The sensor should be 3 wires? i assume you will need to apply power from your universal gauge to the sensor to get a digital output from it. Or that is how the sensors i have seen work.
Another option is to add a different style sensor in place or in addition to the one that is there?
I'd also check that the fly sheel does indeed have a magnet for the pickup signal. I have never looked closely to confirm there is a magnet in there, i just always just assumed.

SUCCESS! I took my portable scope outside and connected to the flywheel RPM sensor (2 wires only) and it generates a nice clean sine wave, at twice the RPM so there must be 2 magnets in there, it was reading 2 KHz which is twice the actual RPM of 1000, confirmed with my model airplane optical tach, I painted a white blotch on the flywheel and it read 1000 RPM (idle). Then did some more research and found that some newer alternators have a P or W terminal on the back, which can be used to supply a signal to a tach, it connects to the diode stack internally and provides pulses. I measured 230 Hz on mine at idle, which when converted to single pulse per revolution is 13,800 RPM, but then most automotive tachs are designed to read correctly based on 4 pulses per rev on an 8 cylinder, 3 on a 6 and 2 on a 4 cylinder engine. I connected my tach to this terminal and it worked, but it read 3,500 RPM when set for an 8 cylinder engine. I took the tach apart and found there are 3 resistors, one for each of the 3 switch positions, that correspond to 4, 6 and 8 cylinders, measured them, did a bit of math and changed the one resistor that was 35K for the 8 cylinder to a 6K and it now reads perfectly, 1,000 RPM, confirmed with the scope on the flywheel sensor all the way up to 3,000 RPM. Yeah! Mounted it below the gauge pod and it looks great, even has a backlight. Hope this helps anyone who wants to add a tach to their Diesel engine. Cheers

 

[kilohertz]

SUCCESS! I took my portable scope outside and connected to the flywheel RPM sensor (2 wires only) and it generates a nice clean sine wave, at twice the RPM so there must be 2 magnets in there, it was reading 2 KHz which is twice the actual RPM of 1000, confirmed with my model airplane optical tach, I painted a white blotch on the flywheel and it read 1000 RPM (idle). Then did some more research and found that some newer alternators have a P or W terminal on the back, which can be used to supply a signal to a tach, it connects to the diode stack internally and provides pulses. I measured 230 Hz on mine at idle, which when converted to single pulse per revolution is 13,800 RPM, but then most automotive tachs are designed to read correctly based on 4 pulses per rev on an 8 cylinder, 3 on a 6 and 2 on a 4 cylinder engine. I connected my tach to this terminal and it worked, but it read 3,500 RPM when set for an 8 cylinder engine. I took the tach apart and found there are 3 resistors, one for each of the 3 switch positions, that correspond to 4, 6 and 8 cylinders, measured them, did a bit of math and changed the one resistor that was 35K for the 8 cylinder to a 6K and it now reads perfectly, 1,000 RPM, confirmed with the scope on the flywheel sensor all the way up to 3,000 RPM. Yeah! Mounted it below the gauge pod and it looks great, even has a backlight. Hope this helps anyone who wants to add a tach to their Diesel engine. Cheers

 

[Tazza]

Nice job working that out.
Glad you had a hand teld tach to confirm everything was dialed in.