Autometer Tach Reading High
Autometer Tach Reading High I just got finished with a lsx swap into my 71 Trans Am. I am running an Autometer Cobalt gauge set on 4 cyl mode. I have sliced into the signal wire with a 12v lead and placed anywhere from 680 ohm - 2.2k ohm 1/2 watt resister between the 12v wire and the signal wire. All of which seem to keep showing my idle at about 1900 rpm. then depending upon which resistor value, it can read up to 4k rpm, then the tach needle drops to 0. Any ideas how to fix this? I dont have the OBD2 port wired yet, and no way to scan the computer or tune it. I was thinking of getting a mail order tune from Frost, but not sure what he could fix to help this?
My tach is on 6cyl mode. Its an autometer designer black. Tried it first on 4cyl (seems to the forum's go-to setting) mode and read wrong, switched to 8cyl and was still wrong...6cyl was just right. I also ran the pick up circuit and resistor (680ohm?) like everyone else has done
Staging Lane
Joined: Jul 2012
Posts: 67
Likes: 1
? on my setup i have the edelbrock msd box but i have a big 5" autometer tach and it reads correct on the 8cly mode and no resistors or anything like that? i dont understand why yall are having trouble. is it because it is the cobalt guage or because it is the 6010 msd box?
You need to take the tach signal wire coming from the PCM and hook it into the signal terminal on the back of the tach. Set the tach for 4 cylinder mode. Hook up 12volt power to the 12+ terminal on the tach and connect the ground terminal to ground. That is all I did on my Autometer Antique tach and it works fine.
See here:
http://www.autometer.com/productPDF/1165.pdf
I just can't remember if mine was set for 4 cyl one pulse or 4 cyl two pulse.
EDIT: Reading my tach's install sheets, mine only had a 4 cyl two pulse selection. So I'd say set yours to 4 cyl two pulse.
http://www.autometer.com/productPDF/1165.pdf
I just can't remember if mine was set for 4 cyl one pulse or 4 cyl two pulse.
EDIT: Reading my tach's install sheets, mine only had a 4 cyl two pulse selection. So I'd say set yours to 4 cyl two pulse.
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what i did was hook a 12v wire to the tach wire with a 680 ohm resistor between the tach wire and the 12v wire, then hook that up to the tach signal wire. The tach worked fine with the old 462 i had. My tach also has dip switches, which allow for only 4 cyl, 6 cyl and 8cyl mode.
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Verdad Gallardo what i did was hook a 12v wire to the tach wire with a 680 ohm resistor between the tach wire and the 12v wire, then hook that up to the tach signal wire. The tach worked fine with the old 462 i had. My tach also has dip switches, which allow for only 4 cyl, 6 cyl and 8cyl mode.
The 12v is not for lighting the tach. The 12v goes to the tach in a different spade and gives the tach power to operate.
The lighting has its own spade on the back of the tach that needs to be connected to a dash light (comes on with parking lights or headlights, etc). The 12v gives the tach power to read the signal and operate.
And again, the signal has it's own spade on the back of the tach to give the signal to the tach.
And then there's also the ground.
i have my tach hooked up directly to the signal wire out of the computer, then had the tuner adjust the settings and its dead perfect... I have the Phantom II gauges, and there is no 4-6-8 switch on the back...
my advice is to hook it up normally then tune the computer for the correct output...
my advice is to hook it up normally then tune the computer for the correct output...
Interesting thread....I have an Auto Meter tach and initially hooked tach signal wire up withe the tach set to 4 cylinder mode and got no reading.
I called Auto Meter and they said tie in a +5V line with a 10K ohm resistor on 4 cylinder mode. A harness builder I know said hook up a 12V line with a 4.7K ohm resistor on 4 cylinder mode. I went with the harness builder recommendation and the tach works, but the needle flutter at idle.
I called Auto Meter and they said tie in a +5V line with a 10K ohm resistor on 4 cylinder mode. A harness builder I know said hook up a 12V line with a 4.7K ohm resistor on 4 cylinder mode. I went with the harness builder recommendation and the tach works, but the needle flutter at idle.
TECH Apprentice
Joined: Nov 2011
Posts: 337
Likes: 1
From: Murray, KY
I'm not trying to be a jerk, but I want to correct that statement.
The 12v is not for lighting the tach. The 12v goes to the tach in a different spade and gives the tach power to operate.
The lighting has its own spade on the back of the tach that needs to be connected to a dash light (comes on with parking lights or headlights, etc). The 12v gives the tach power to read the signal and operate.
And again, the signal has it's own spade on the back of the tach to give the signal to the tach.
And then there's also the ground.
The 12v is not for lighting the tach. The 12v goes to the tach in a different spade and gives the tach power to operate.
The lighting has its own spade on the back of the tach that needs to be connected to a dash light (comes on with parking lights or headlights, etc). The 12v gives the tach power to read the signal and operate.
And again, the signal has it's own spade on the back of the tach to give the signal to the tach.
And then there's also the ground.
Alright guys, got my computer back from Frost with a new tune on it. I have now tried the tach on every setting, with or without the 12v wire attached and numerous resistors in line. The most I get is either it giving me the correct idle and then falling down to 0 after I give it some throttle, or it showing idle at 1850 rpm and revving to 3000 with before falling to 0. Does anyone think it could be in the tune, or possibly the tach?
I just noticed some are using 1/2 watt resistors and other are using 1/4 watt resistors. I have been using 1/2 watt, do you think this could be the problem?
Nevermind...just tried a bunch of 1/4 watt resistors and it didnt make a difference...Im just going to wait to hear back from Autometer.
Nevermind...just tried a bunch of 1/4 watt resistors and it didnt make a difference...Im just going to wait to hear back from Autometer.
Last edited by stangs400; Oct 4, 2012 at 11:55 AM.
