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STILL LEARNING
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Discussion Starter · #1 ·
What exactly does the tach use for a signal? Does anyone run an aftermarket tach? How/ what kind of signal did you use. And what model number tach did you use
 

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The tach signal comes from the PCM, pin #50 by my schematic for the OBS'.

Dave
 

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I am curious why you want to do this? You could also do something that runs off the OBD port for a tach signal.
 

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Crazy Talk
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i put a shift light on mine. only thing is there must be 2 different tach signals on different wires. the wire i used i had to set the light for like 9k or so to come on at like 3500.
 

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Pin #49 on the PCM is from the CPS to the PCM, carrying the raw pulses from the tonewheel on the cam gear. Pin #50 is as Smokyred mentioned, it runs from the PCM up to the instrument cluster and directly drives the tachometer. I haven't looked at the signal on pin #50, but it is probably generating a similar waveform to what a gasser gets for its tach.

I have a tach with shift light and recall in my truck, running directly off of the sensor wire on pin #49. I wanted to use the raw data from the sensor to be sure and have an accurate RPM reading. The tach is a prototype of a new line we are about to release, if anyone is interested in more details please drop me a PM.

Regards,
Michael Pliska
 

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STILL LEARNING
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Discussion Starter · #6 ·
I am curious why you want to do this? You could also do something that runs off the OBD port for a tach signal.
I am putting a PSd in place of my guttless 6.9 in my 86 but I am using my 86 gauge cluster. I DO NOT MANT TO USE THE 95 Cluster
 

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Crazy Talk
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Pin #49 on the PCM is from the CPS to the PCM, carrying the raw pulses from the tonewheel on the cam gear. Pin #50 is as Smokyred mentioned, it runs from the PCM up to the instrument cluster and directly drives the tachometer. I haven't looked at the signal on pin #50, but it is probably generating a similar waveform to what a gasser gets for its tach.

I have a tach with shift light and recall in my truck, running directly off of the sensor wire on pin #49. I wanted to use the raw data from the sensor to be sure and have an accurate RPM reading. The tach is a prototype of a new line we are about to release, if anyone is interested in more details please drop me a PM.

Regards,
Michael Pliska
shoot me a pm on the tach. also why would mine read so off?
 

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STILL LEARNING
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Discussion Starter · #8 ·
So am i stuck having to use the PSD instrument cluster?
 

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So am i stuck having to use the PSD instrument cluster?
You may be, my 6.9 that I had was an 83, so it didn't have the option of a tach, so I can't be of help from that end.

Just thinking out loud here, but maybe you can take the guts of the PSD tach, and put them into the back of the older instrument panel.

Dave
 

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Discussion Starter · #10 ·
You may be, my 6.9 that I had was an 83, so it didn't have the option of a tach, so I can't be of help from that end.

Just thinking out loud here, but maybe you can take the guts of the PSD tach, and put them into the back of the older instrument panel.

Dave
I was thinking that too but it think the tachs have a different sweep
 

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^^^ +1; the gasser tach has a much higher range. It would take some tweaking, but you could do as suggested above, and use a computer and some mad graffix skillz and make your own number face.
 

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Discussion Starter · #12 ·
I have the factory 86 diesel tach and it is a waffel patten. Not quite sure how to copy that
 

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shoot me a pm on the tach. also why would mine read so off?
You're probably on the raw CPS signal, which is 12 pulses per rev. If the shift light is for a V8 gasser, it's looking for 4 pulses per rev, so you should have to triple the setting.
 
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