delete ECM on 12V, but keep factory tach?

Hurley

Hurley

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Can I keep the factory tach functional if I remove the ECM/computer/whatever from my 12 valve?
 
Short answer is the factory ecm runs all the factory gauges including the tachometer.
 
Sounds like a good time for a badass sheetmetal dash with a full array of gauges
 
It's been a while guys, hi, hows it going?

I've thinned my harness to the bare essentials, all while trying to keep the wiring for factory gauges, wipers and light circuitry- Everything else is gone. gone. I'm talking stage-11 weight reduction in high gear. Yes, a sheetmetal dash is in the plans, however being a cheapass I'm going to keep the factory gauge cluster for the time being.

The tachometer signal is the only one that actually has the ECM in series in the wiring - i 'think' that the ECM actually converts the signal for the gauge itself, but that's what I'm wanting to confirm with this thread. FWIW, any of the other gauge senders that send a signal to the ecm do so in parallel for other functions - cruise, ac, etc. I'll handle the alternator and ASD relay wiring separately.
 
In the long run I think you'd save money just pulling the trigger and building a dash, it's really not that hard to do with an aftermarket harness.
 
Bump for the original question-


and yes, it's getting a sheetmetal dash regardless of which gauges I use
 
Hurley said:
It's been a while guys, hi, hows it going?

I've thinned my harness to the bare essentials, all while trying to keep the wiring for factory gauges, wipers and light circuitry- Everything else is gone. gone. I'm talking stage-11 weight reduction in high gear. Yes, a sheetmetal dash is in the plans, however being a cheapass I'm going to keep the factory gauge cluster for the time being.

The tachometer signal is the only one that actually has the ECM in series in the wiring - i 'think' that the ECM actually converts the signal for the gauge itself, but that's what I'm wanting to confirm with this thread. FWIW, any of the other gauge senders that send a signal to the ecm do so in parallel for other functions - cruise, ac, etc. I'll handle the alternator and ASD relay wiring separately.
Click to expand...

Honestly, if you took a multimeter, and measured what inputs to the tach made the meter move, you could probably program an arduino (or smaller) to do this job. 12V's run off the harmonic balancer which only has one notch correct? That would make this super easy. One spike = one rotation, duration between spikes, convert to a frequency, convert proportionally to the voltage input needed for the gauge, and done.
 
Or you could use a MeCan and install a nice touch screen in your dash and display the entire SOB on one screen and data log and yada yada yada if you got some cash and some time to learn how to program it. :D

http://www.fwmurphy.com/products/can-io-accessories/mecan

I'm not using a MeCAN but this is one of my older screens. You can configure the entire thing to your liking with some time and ability to modify graphics.

attachment.php
 

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CorneliusRox said:
Honestly, if you took a multimeter, and measured what inputs to the tach made the meter move, you could probably program an arduino (or smaller) to do this job. 12V's run off the harmonic balancer which only has one notch correct? That would make this super easy. One spike = one rotation, duration between spikes, convert to a frequency, convert proportionally to the voltage input needed for the gauge, and done.
Click to expand...


Tach runs off of a pulse output from the ECM, so just need to make the frequency work.
 
zstroken said:
Tach runs off of a pulse output from the ECM, so just need to make the frequency work.
Click to expand...

Arduino's do have a port for PWM!

There's some legwork involved in figuring out what the input range is, but I think it's definitely doable. Especially if you've got a spare gauge and a breadboard to experiment with.
 
4x4dually said:
Or you could use a MeCan and install a nice touch screen in your dash and display the entire SOB on one screen and data log and yada yada yada if you got some cash and some time to learn how to program it. :D

http://www.fwmurphy.com/products/can-io-accessories/mecan

I'm not using a MeCAN but this is one of my older screens. You can configure the entire thing to your liking with some time and ability to modify graphics.
Click to expand...

That's pretty sweet. How much do they cost, what inputs do they have, do they have algorithms set up for different sensors and what not, and does it output to a USB or something to use a tablet as a monitor?
 
Pull up Resistor

Do some more searching. I needed a tach for my '71 Fummins and found where some guys had wired in an aftermarket tach to the factory sending unit. Here is what I did. The wording is poached from somewhere else. I can't take credit for it. It works great.


Crank position sensor wiring: the black w/white wire for ground, the purple one for the coil and the gray one for the 12v.
the red wire on the cps is 12v ignition, the black wire is ground, and the green wire goes to the coil pin on the back of the tach.

on The tach side you need to solder a 1k ohm resistor across the 12v pin and the coil pin. this is acting as a pull up resister so that the coil pin sees 12v when the CPS sees the metal of the harmonic balancer. when the CPS passes over the gaps in the balancer, it grounds the coil pin, so the tach sees a low. this creates the pulse that the tach is looking for. however, the balancer has only two slots in it, creating two pulses per revolution. the stock v8 tach is looking for 4 pulses per revolution . if you are using an aftermarket tach that can be changed from 8/6/ or 4 cyl, simply put the switches to 4 cyl and your tach will read like it is suppose to. if it won't change to 4 cyl or you are using a stock tach then you will either need to machine two more notches in the balancer 180 deg apart from each other so that you now have 4 equally spaced notches in your balancer, or modify the back of your tach board.
 
4x4dually said:
Or you could use a MeCan and install a nice touch screen in your dash and display the entire SOB on one screen and data log and yada yada yada if you got some cash and some time to learn how to program it. :D

http://www.fwmurphy.com/products/can-io-accessories/mecan

I'm not using a MeCAN but this is one of my older screens. You can configure the entire thing to your liking with some time and ability to modify graphics.

attachment.php
Click to expand...

It says it outputs CanBus. Do you run it through a pass-through box and then to a tablet to get a display like that? I doubt I'd ever do it. But evrytime I look at the "oil pressure gauge" in my dash, it annoys me to no end. I don't have gauges for the other fun stuff either so that has me thinking.
 
Yes. It converts it to J1939 output via CanBus. I just ran that to a display. Currently I use a PV750. Don't google the price. :D
 
4x4dually said:
Yes. It converts it to J1939 output via CanBus. I just ran that to a display. Currently I use a PV750. Don't google the price. :D
Click to expand...

Gotcha. I've got a little bluetooth OBD2 plug that hooks up to the Android App Torque that does the same thing. I think what OP was asking for was a way to display things when there is no network. He wants to gut the system and only have the basics, like a tach. In that case, I don't think the J1939 solution would work.
 
It would work find if he installs a MeCAN and a PV101, the old school Murphy display. It only reads J1939, not OBDII.

Probably find one on Ebay cheap.

powerview_pv101.gif
 
4x4dually said:
It would work find if he installs a MeCAN and a PV101, the old school Murphy display. It only reads J1939, not OBDII.

Probably find one on Ebay cheap.

powerview_pv101.gif
Click to expand...

Ah, sorry. I didn't realize you were still talking about using the MeCAN. That makes more sense.
 
Hurley said:
I just want the factory tach to work without the ECM :eek:
Click to expand...

Well, it sounds like he's onto something \/ \/ \/
Please report back!

fordpickupman said:
Do some more searching. I needed a tach for my '71 Fummins and found where some guys had wired in an aftermarket tach to the factory sending unit. Here is what I did. The wording is poached from somewhere else. I can't take credit for it. It works great.


Crank position sensor wiring: the black w/white wire for ground, the purple one for the coil and the gray one for the 12v.
the red wire on the cps is 12v ignition, the black wire is ground, and the green wire goes to the coil pin on the back of the tach.

on The tach side you need to solder a 1k ohm resistor across the 12v pin and the coil pin. this is acting as a pull up resister so that the coil pin sees 12v when the CPS sees the metal of the harmonic balancer. when the CPS passes over the gaps in the balancer, it grounds the coil pin, so the tach sees a low. this creates the pulse that the tach is looking for. however, the balancer has only two slots in it, creating two pulses per revolution. the stock v8 tach is looking for 4 pulses per revolution . if you are using an aftermarket tach that can be changed from 8/6/ or 4 cyl, simply put the switches to 4 cyl and your tach will read like it is suppose to. if it won't change to 4 cyl or you are using a stock tach then you will either need to machine two more notches in the balancer 180 deg apart from each other so that you now have 4 equally spaced notches in your balancer, or modify the back of your tach board.
Click to expand...
 
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