problem with aftermarket tach
#1
06-12-2006 | 11:30 PM
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problem with aftermarket tach
Okay i just finished wiring up an aftermarket electronic tach. I have power and the light works, but I am not getting any signal from the tachwire.
I used the gray wire with a light blue stripe that is behind the gauge cluster (which according to my haynes manual and a search on here) says that this is the right wire. I took a voltmeter to it and only get between .3v an .8v at WOT. Im assuming this is the issue, but am not sure what could cause this. Should I be looking for the wire coming directly from the PCM and hooking it up there? or is it possibly the PCM just not working properly?
I used the gray wire with a light blue stripe that is behind the gauge cluster (which according to my haynes manual and a search on here) says that this is the right wire. I took a voltmeter to it and only get between .3v an .8v at WOT. Im assuming this is the issue, but am not sure what could cause this. Should I be looking for the wire coming directly from the PCM and hooking it up there? or is it possibly the PCM just not working properly?
#2
06-13-2006 | 02:32 PM
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RE: problem with aftermarket tach
'95 Neon, per chance?
Aftermarket tachs do not go off a voltage signal, they go off a pulsed square wave. The Neon factory tach is voltage driven (all 1st gens). If your '95 Neon did not come with a factory tach, an aftermarket tach will not work. The best I can tell is it uses a different crank signal. I know it's not the PCM, because I've had 3 different ones in my '95. '95 Neons that had a factory tach installed don't seem to have this problem, and all of the '96-up cars hook up and go with no problem. I'm sure there are exceptions to the rule out there, but I think I've only heard of one or two '95ers getting a useable signal.
The best way to get a good signal is with a tach driver (MSD calls theirs a tach "adapter", which is technically incorrect). I'd have to look up the part number (8012 or 8013, something like that), but it only runs $30 or so at Summit or Jegs. There's a ghetto way by using a resistor and diode setup tapped into the ground wires for the coilpack. But once you get up to higher RPM's (5k or so) and dwell time increases to the point the signals overlap, you can kiss an accurate signal goodbye (from experience) as the needle bounces all over the place.
Best of luck!
Aftermarket tachs do not go off a voltage signal, they go off a pulsed square wave. The Neon factory tach is voltage driven (all 1st gens). If your '95 Neon did not come with a factory tach, an aftermarket tach will not work. The best I can tell is it uses a different crank signal. I know it's not the PCM, because I've had 3 different ones in my '95. '95 Neons that had a factory tach installed don't seem to have this problem, and all of the '96-up cars hook up and go with no problem. I'm sure there are exceptions to the rule out there, but I think I've only heard of one or two '95ers getting a useable signal.
The best way to get a good signal is with a tach driver (MSD calls theirs a tach "adapter", which is technically incorrect). I'd have to look up the part number (8012 or 8013, something like that), but it only runs $30 or so at Summit or Jegs. There's a ghetto way by using a resistor and diode setup tapped into the ground wires for the coilpack. But once you get up to higher RPM's (5k or so) and dwell time increases to the point the signals overlap, you can kiss an accurate signal goodbye (from experience) as the needle bounces all over the place.
Best of luck!