Hey guys,

I know there have been a lot of write ups about this, but I'd thought I should pick a few more brains....

So I am a die hard I6 guy looking for a factory tach, and I couldn't justify buying one that goes up to 6k! The diesel tach is what I want.

From my understanding, the diesel tach reads a different signal. In order to make it work, I would need some electronic device to change the signal.

So I guess my question to you guys is, Is this the only way to do it?? If so, what do I need to look for?

 

I have some info on tachs, both gas and diesel, on my web site here: Tachometers - ??Gary's Garagemahal. But, there are others better qualified than I to speak to how to drive the diesel tach.

 

wow very interesting.... I might just buy a different tach

 

From what I've read the diesel tach requires a completely different signal that the gas tachs, and that would mean quite a bit of electronic work to run it on a gas engine. But the gas tachs all run off the ignition signal, which your truck should be wired for if it came with gauges instead of idiot lights, and will be plug and play.

 

The diesel tach reads many teeth on the drive gear that runs the injection pump. No idea how you would convert that to run off a ignition coil of the 300 six cylinder.

 

Diesel guys generally have the opposite problem: gas engine tachs use a signal from the coil... so if you are doing a diesel swap or similar project where there are no factory tach components it can be hard to add an aftermarket tach. Before there were programmable aftermarket tachs one common solution was to JB weld four magnets or steel nibs onto the vibration damper or crank pulley. Then build a bracket to hold a magnetic sensor (cam or crank position sensor, ABS wheel rotation sensor etc.,) then hook the signal to a V8 tachometer and you get 4 pulses per crank revolution just like a coil signal...

So... I have been thinking about a reverse scenario for I-6 guys. The medium duty 4,000 and 4,500 rpm gas engine tachs are quite rare. Bullnose diesel tachs are rare as well, but much more find-able than the medium duty tachs. The 6.9 IDI reads the signal from the injection pump gear teeth. The gear has 106 teeth and rotates once for every two crank revolutions. Therefore the diesel tach needs 53 pulses per revolution to read correctly. In theory then (instead of trying to re-engineer the electronics and fine voltage differences) one could mount a 53 tooth star wheel on the crank pulley and build a bracket with a magnetic pick-up to read the teeth. It is far from being an elegant solution, but depending on your fabrication skills. It could be executed well. The pay off of having a low range factory tachometer in the dash would be worth it in my opinion, but I place a much higher value on stock appearance than most owners. It is very frustrating that Ford did not just install 4,000 rpm tachs on all I-6 trucks from the factory. The unit already existed for the big trucks, so why they did not do that is beyond me.

 

That would be an interesting solution.

 

Looking for a solution to use the tachometer leads coming out of the timing gear housing to attach a tachometer to a dash( 2.8inch diameter) mount on my 1930 Buick rat rod. Any tachometer suggestions? Any tachometer out there can be adapted to fit this application. I’m looking for an inexpensive solution.

 

I'm confused. Are you saying you have a 1986 Ford 6.9L diesel in your 1930 Buick and need a tach that is 2.8" in diameter? And, I presume, it needs to mount like most aftermarket gauges, meaning it slips into a round hole and is secured with a U-shaped bracket from the rear? Or, is it to be in a round housing strapped to the steering wheel or dash?

I'm not aware of such a tach, but would think you could make one from an 80's Ford diesel tach. Cut the face round and stuff it in a housing.

 

There are aftermarket tachometers that can be programmed to work with the IDI factory sensor. The injection pump gear has 106 teeth and revolves once for every two crank revolutions. Therefore if you program the gauge for 53 pulses per engine revolution it should read correctly. I believe Isspro makes one.

 

Still have not found a bull nose tach in my area..... but I just picked up a diesel cluster for my 89 F250. Even though its not a bull nose era but the tachs are all about the same. Once I reverse engineer the diesel tach and compare with gas, I then change the diesel tach's circuitry to read like the gas. Should be simple resistor and/or capacitor change.........