Tach signal and EFI, Megasquirters and Subaru converters please read... |
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Tach signal and EFI, Megasquirters and Subaru converters please read... |
falcor75 |
Jul 25 2016, 01:39 AM
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#1
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Senior Member Group: Members Posts: 1,579 Joined: 22-November 12 From: Sweden Member No.: 15,176 Region Association: Scandinavia |
I'm running my 2.0 four cylinder with an aftermarket ECU.
In the settings for the tach signal I've selected 12v, 50% duty and this worked fine for a few months of testing. The day before my dyno session the tach started behaving wierdly. It would start up fine but after a little bit of running it would settle between 3k-4k rpm. Revving the engine would momentarily get it back to normal but after a few seconds at constant rpm it would return to its new favorite position. Any ideas what could be causing this? |
Series9 |
Jul 25 2016, 06:52 AM
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#2
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Lesbians taste like chicken. Group: Members Posts: 5,444 Joined: 22-August 04 From: DeLand, FL Member No.: 2,602 Region Association: South East States |
I'm running my 2.0 four cylinder with an aftermarket ECU. In the settings for the tach signal I've selected 12v, 50% duty and this worked fine for a few months of testing. The day before my dyno session the tach started behaving wierdly. It would start up fine but after a little bit of running it would settle between 3k-4k rpm. Revving the engine would momentarily get it back to normal but after a few seconds at constant rpm it would return to its new favorite position. Any ideas what could be causing this? I'm going to say a high-resistance terminal is the problem. Some of the stock tachs work with modern ECUs, but many require an amplifier. The computer signal is really a bit weak to run an old tach. The easiest solution is to grab an Autometer tach from your local store. I have found a few wraps of gaffer's tape will create a nice friction-fit. Otherwise, the installation of a signal amplifier is also easy. |
McMark |
Jul 25 2016, 06:59 AM
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#3
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914 Freak! Group: Retired Admin Posts: 20,179 Joined: 13-March 03 From: Grand Rapids, MI Member No.: 419 Region Association: None |
(IMG:style_emoticons/default/agree.gif) except about the Autometer Tach. Works but it's not original. (IMG:style_emoticons/default/tongue.gif) (IMG:style_emoticons/default/laugh.gif)
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falcor75 |
Jul 25 2016, 07:18 AM
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#4
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Senior Member Group: Members Posts: 1,579 Joined: 22-November 12 From: Sweden Member No.: 15,176 Region Association: Scandinavia |
Yeah I want to use the orginal tach. Anyone know if a signal amplifier that works? I googled some homebuilt stuff but I'd rather buy something off the shelf.
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timothy_nd28 |
Jul 25 2016, 09:23 AM
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#5
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Advanced Member Group: Members Posts: 2,299 Joined: 25-September 07 From: IN Member No.: 8,154 Region Association: Upper MidWest |
Google pull up resistor
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Dtjaden |
Jul 25 2016, 09:45 AM
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#6
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Member Group: Members Posts: 232 Joined: 25-May 13 From: Morgan Hill, CA Member No.: 15,915 Region Association: Northern California |
Although I built my own here is a commercial option:
http://www.casperselectronics.com/cart/ind...&search=Vdo |
McMark |
Jul 25 2016, 11:04 AM
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#7
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914 Freak! Group: Retired Admin Posts: 20,179 Joined: 13-March 03 From: Grand Rapids, MI Member No.: 419 Region Association: None |
http://www.jegs.com/i/MSD-Ignition/121/8920/10002/-1
(IMG:http://www.914world.com/bbs2/uploads_offsite/www.jegs.com-419-1469466277.1.jpg) Wiring-- Red: +12v Black: Ground White: Black/Purple wire from engine/coil Violet: To tachometer, where the black/purple used to go. You can install this behind the gauge and use all the wires off the tach for connections. |
914forme |
Jul 25 2016, 11:22 AM
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#8
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Times a wastin', get wrenchin'! Group: Members Posts: 3,896 Joined: 24-July 04 From: Dayton, Ohio Member No.: 2,388 Region Association: None |
Google pull up resistor (IMG:style_emoticons/default/agree.gif) or read Timothy's great writeup on how to convert your old tach guts to new tach guts. |
stugray |
Jul 25 2016, 12:54 PM
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#9
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Advanced Member Group: Members Posts: 3,824 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
Where are you grabbing the tach signal?
If it is from the coil (points) then it is not just 12Volts, but more like +/-200. I have a homebuilt datalogger (ECU) and I pull the signal from the optical sensor in my Mallory Unilite. It IS a nice clean 0-12VDC signal, but unlikely it is 50% Duty Cycle. Can you put an oscope on the signal and look at it? If you dont have access to an oscope, you could use one of these for $26 US: http://www.banggood.com/DSO138-DIY-Digital...-p-1051616.html But if you are not sure of the signal amplitude you would use an attenuator (variable resistor) to first check the signal to avoid blowing up your scope. |
falcor75 |
Jul 25 2016, 02:19 PM
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#10
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Senior Member Group: Members Posts: 1,579 Joined: 22-November 12 From: Sweden Member No.: 15,176 Region Association: Scandinavia |
The signal is on a dedicated tach output from the ECU, and I can set it to either 12v or 5v with 50% duty cycle or a duty cycle I choose myself.
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stugray |
Jul 25 2016, 02:30 PM
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#11
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Advanced Member Group: Members Posts: 3,824 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
The signal is on a dedicated tach output from the ECU, and I can set it to either 12v or 5v with 50% duty cycle or a duty cycle I choose myself. So the ECU reads the actual tach signal from the coil, then 'conditions' it and routes it back out to the TACH as a +12 or +5VDC signal? That sounds a lot like my setup using the MSD 6AL. There is a +12V 'TACH' signal that comes out but the Stock TACH could not read it. So I used the MSD Tach-Adapt like shown above. HOWEVER - the TACH signal that goes INTO the Tach Adapt has to be capable of relatively high current, so check to be sure the Megasquirt tach signal you intend to use is capable before you try it or you could fry it. |
falcor75 |
Jul 26 2016, 12:00 AM
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#12
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Senior Member Group: Members Posts: 1,579 Joined: 22-November 12 From: Sweden Member No.: 15,176 Region Association: Scandinavia |
The signal is on a dedicated tach output from the ECU, and I can set it to either 12v or 5v with 50% duty cycle or a duty cycle I choose myself. So the ECU reads the actual tach signal from the coil, then 'conditions' it and routes it back out to the TACH as a +12 or +5VDC signal? That sounds a lot like my setup using the MSD 6AL. There is a +12V 'TACH' signal that comes out but the Stock TACH could not read it. So I used the MSD Tach-Adapt like shown above. HOWEVER - the TACH signal that goes INTO the Tach Adapt has to be capable of relatively high current, so check to be sure the Megasquirt tach signal you intend to use is capable before you try it or you could fry it. Oops, I'm sorry I misunderstood you. My ecu gets the crank speed signal from the crank position sensor and a 36-1 tooth wheel mounted behind the fan. The ecu can then send this signal out as either a 5v or 12v signal depend what I select in the setup. I guess I'll need to build an amplifier circuit since I dont really want to open up the tach to modify it. |
JamesM |
Jul 26 2016, 12:27 AM
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#13
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Senior Member Group: Members Posts: 1,888 Joined: 6-April 06 From: Kearns, UT Member No.: 5,834 Region Association: Intermountain Region |
Yeah I want to use the orginal tach. Anyone know if a signal amplifier that works? I googled some homebuilt stuff but I'd rather buy something off the shelf. You can modify the stock tach to work without a signal amp. I do not recall the specifics off the top of my head but the info is out there if you search for it, its a very simple mod. I did that and the mod to eliminate the tach bounce about 10 years ago and its been fine triggering off my Megasquirt+MSD setup ever since. |
mjrrti |
Jul 26 2016, 12:35 AM
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#14
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High Desert Member Group: Members Posts: 49 Joined: 4-February 14 From: Apple Valley, Ca Member No.: 16,959 Region Association: Southern California |
[size=5]I am using a cool adapter called tach adapt with a Suby controlled by a link computer on my car. It converts a modern low voltage signal to what your old tach needs. Also will convert 4,6,or 8 cyl signal to 4,6,or 8 tachs. I somehow stumbled onto the website and mine works great. Pelican sells them or you can buy direct. AshlockTech.com Good luck.
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JamesM |
Jul 26 2016, 10:06 AM
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#15
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Senior Member Group: Members Posts: 1,888 Joined: 6-April 06 From: Kearns, UT Member No.: 5,834 Region Association: Intermountain Region |
Yeah I want to use the orginal tach. Anyone know if a signal amplifier that works? I googled some homebuilt stuff but I'd rather buy something off the shelf. You can modify the stock tach to work without a signal amp. I do not recall the specifics off the top of my head but the info is out there if you search for it, its a very simple mod. I did that and the mod to eliminate the tach bounce about 10 years ago and its been fine triggering off my Megasquirt+MSD setup ever since. Found my notes, fix was to jumper over the primary input resistor, super easy single wire addition in the tach. |
falcor75 |
Jul 27 2016, 08:45 AM
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#16
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Senior Member Group: Members Posts: 1,579 Joined: 22-November 12 From: Sweden Member No.: 15,176 Region Association: Scandinavia |
Did some testing today...
First i borrowed an Autometer SportComp tach from friend and hooked that up to the ECU output cable. The autometer tach is spot on what the ECU is sending out. Popped the VDO tach from the cluster and pulled the signal wire from it, it still shows 3000 rpm! (IMG:style_emoticons/default/blink.gif) So, electronics isnt my strong suite but I'm guessing one of the internal components of the tach has failed somehow? |
Series9 |
Jul 27 2016, 12:46 PM
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#17
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Lesbians taste like chicken. Group: Members Posts: 5,444 Joined: 22-August 04 From: DeLand, FL Member No.: 2,602 Region Association: South East States |
Did some testing today... First i borrowed an Autometer SportComp tach from friend and hooked that up to the ECU output cable. The autometer tach is spot on what the ECU is sending out. Popped the VDO tach from the cluster and pulled the signal wire from it, it still shows 3000 rpm! (IMG:style_emoticons/default/blink.gif) So, electronics isnt my strong suite but I'm guessing one of the internal components of the tach has failed somehow? Like I said, you can throw an Autometer tach in there and gain perfect (not bouncy) function plus a shift light if you like. A /4 VDO tach is nothing special, except that it looks like it goes there. |
Series9 |
Jul 27 2016, 12:52 PM
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#18
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Lesbians taste like chicken. Group: Members Posts: 5,444 Joined: 22-August 04 From: DeLand, FL Member No.: 2,602 Region Association: South East States |
Is this really that different from a stock tach?
It has several cool functions and works perfectly with your ECU. Attached image(s) |
falcor75 |
Jul 27 2016, 02:35 PM
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#19
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Senior Member Group: Members Posts: 1,579 Joined: 22-November 12 From: Sweden Member No.: 15,176 Region Association: Scandinavia |
Is this really that different from a stock tach? It has several cool functions and works perfectly with your ECU. Yeah I know it would work but its ugly and looks like it should be in a NOS'd Honda rather than a seventies Porsche.... (IMG:style_emoticons/default/biggrin.gif) |
Series9 |
Jul 28 2016, 07:55 AM
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#20
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Lesbians taste like chicken. Group: Members Posts: 5,444 Joined: 22-August 04 From: DeLand, FL Member No.: 2,602 Region Association: South East States |
I bet North Hollywood or Palo Alto Speedometer can put modern guts in an old tach. That would be the perfect solution. |
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