It is hooked up but I have not run it yet.

I don't see why it wouldn't considering the tach itself has nothing to do with which engine it is behind. The difference is in the wiring on the printed circuit.

 

All depends if the sparks per revolution are being normalized or not prior to being an input to the tach itself.

 

Like I said, I believe it's all in the circuit.

Normally tachs from I6's and V8's are the same. The only thing that is different is an additional ground for the I6 tach that exists in the circuit film/wiring harness.

 

Yes, I know, I know... this is a six year old thread... just wondering if anyone ever found out if the tach worked correctly. I found one just like it, was hoping to use it with a 6.9 IDI diesel. I don't know how the injection pump gear magnetic pulse sender signal compares to the distributer signal but I thought I'd give it a try. The donor was a 1980 F700 with either a 370 or 429 V8. Anyone using one of these 4K tach heads have any comments or advice?

 

You can find 4500 RPM diesel tachs in the yards. I'd definitely opt to go that route. I think the signal is very similar; the tach sensor is just a Hall-effect pickup, but the number of pulses per crank revolution is almost definitely different than a gasser.

 

Okay, that's what I was afraid of. I'm pretty sure I've seen the correct diesel tachs in the junkyard before but never paid much attention since mine was working. Now that I'm looking I can't find any, and the last one that came up on eBay was $195 which isn't happening. Maybe I should post in the junkyard wish list to see if anyone can get one for a "decent" price.

Edit: this is for my friend from Czech Republic, he flew over here last year and bought a truck to ship home. I am just trying to source a few missing items for him as he will have zero parts availability in his country once the truck is shipped. If anyone reading this thread can help out please PM me.

 

Is the the guy from Prague?

Anyway, in addition to the number of pulses per revolution, the shape of the pulses with be dramatically different. The gasser' signal comes off the bottom side of the coil and goes up to something like 30v with lots and lots of ringing on it. The diesel's signal should be more like a 12v square wave with a bit of noise from the environment. So the tach's will have quite different filter circuitry on the front end, and I'd bet the diesel's will be much simpler and may not handle the gasser signal nicely.

 

Thanks Gary, yes, this is for Jan (Romel77) and he is from Prague. I have his truck at my house until he can resolve the details of shipping and registration at his end, then I will take it to the port in Los Angeles.

From what I can tell the IDI pump gear has 53 teeth and turns once for every two crank revolutions. So 26 pulses vs 4. Not going to work. Not to mention the voltage problem. I don't know if anyone here is still looking for a 4K tach, but obviously I have one and it's not doing me much good.

 

Well, I'm sure he appreciated that you tried. And, I'm sure he'll appreciate that you are willing to take it to the port in LA. That's a hike for you.

On the tach, all may not be lost. While most of us won't want a tach that only goes to 4k, I think by replacing the faceplate with a 6k one and running the tach in 6 cylinder mode you'd get 5,333 indicated at 6000 engine RPM. And, on the normal tach's for these trucks there's a trim pot so maybe even that can be dialed in.

 

4000 would probably be enough for a 6.9, the maximum governed engine speed is somewhere around 3800 RPM.

 

So the tach pickup is reading the gear teeth of the pump? The next time I come across a diesel tach at the junk yard, I'm going to get it and see how to modify it to use off a ignition coil tach side. I have the 300 I6 engine and after 3K its all noise and no go so a 4K tach will be good.

 

In post #23 of this thread NumberDummy says the big F series trucks 1979-1989 were available with the I-6, and in post #13 he says there were two different 4000 rpm tachs listed. You might yet find a factory 4K tach for the I-6. I think making the diesel tach work would be quite a challenge. Some of the 8.2 Detroit diesel equipped trucks took the tach reading off the flywheel gear.

Edit: or you could try the tach I pulled and mate it to an I-6 circuit ribbon and see if it works...

 

Quick bump on this topic since I found some info that may help other diesel guys or I-6 guys...

While this tach will not work off a signal from an IP gear, you can make a bracket to mount just about any 2 wire crank position sensor or abs sensor to "read" the 4 bolts on the crank pulley. Boom, 4 pulses and the gas Hall effect tach will work. In theory if you were trying to use a 4,500 diesel tach with an I-6 you could bolt a plate with 26 slots onto your crank pulley and do the same thing.

I don't know about sensor voltage and all of that, but this is a trick many have used to get a gas tach working on their diesel swap. I also recall a thread on how to make your own cheap diesel tach sensor out of a GM crank position sensor, so it must be close enough. Just thought I'd throw this out there in case it helps someone down the line.

 

Reps to you for that. Good info.

 

That is one way to get that tach signal, but a little more involved for me to do. Once I find a diesel tach, I'll figure out which resistors need changing to get a correct reading from it with the I6's 3 pulse per rev signal. As a electronic tech, it will be easy to do for me. Once I figure it out, I'll post it here for sure!