[DeTomaso] Pantera Tach Shows 0 at Cold Idle

Mike Reilly reillyms at live.com
Thu Dec 31 14:25:38 EST 2020


Hi Doug.  I made the tach ground the same place Jon Haas instructed to ground the ICS board which was a dashboard mounting screw to the metal body structure.  I’ll have to try your suggestion of using a long lead to the battery (-) terminal to ensure a solid ground for testing the situation : )   Thanks, Mike

From: Doug Braun<mailto:doug351c at gmail.com>
Sent: Wednesday, December 30, 2020 11:48 AM
To: Mike Reilly<mailto:reillyms at live.com>
Cc: dennis617 at aol.com<mailto:dennis617 at aol.com>; DeTomaso at server.detomasolist.com<mailto:DeTomaso at server.detomasolist.com>
Subject: Re: [DeTomaso] Pantera Tach Shows 0 at Cold Idle

Mike,

I see that you tried a second tach ground already but where did you make your connections?
I recommend you have a helper touch one end of a wire directly to the battery's (-) terminal while you touch the other end to the tach's case.

Doug Braun
blue 73L #5505

On Wed, Dec 30, 2020 at 8:58 AM Mike Reilly <reillyms at live.com<mailto:reillyms at live.com>> wrote:
   Hi all.  Thanks for the input.  I suspect a ground issue somewhere in
   the circuit which I'll try to run down.  Although I did try giving the
   tach it's own ground wire but that didn't change the behavior.  I did
   install a new fuse box and ignition switch controller (ISC) from Jon
   Haas so I may have caused some grounding issue as I moved wires
   around.  I did trouble shoot with Jon months ago but all his products
   seemed to be working as designed.  It was doing this before I switch to
   the new fuse box.  I was hoping the new fuse box would help.  It hadn't
   done it before the ISC was installed but I also had a no start issue
   then due to a bad ignition switch.  So I was touching lots of wiring
   then.


   I'll have some detective work to do here and may need to trace the
   circuit and check everything as folks have suggested.  I'll probably
   reach out to Jon for any further suggestions as well.  Fun with decades
   old wiring : )


   Dennis, I have a DuraSpark distributor and electronic ignition system
   that's been in the car since 1992 and it didn't require a tach
   adaptor.  I only recently had this problem come up so I don't think
   it's my ignition system : (


   Thanks, Mike


   From: [1]dennis617 at aol.com<mailto:dennis617 at aol.com>
   Sent: Wednesday, December 30, 2020 6:44 AM
   To: [2]reillyms at live.com<mailto:reillyms at live.com>; [3]detomaso at server.detomasolist.com<mailto:detomaso at server.detomasolist.com>
   Subject: RE: [DeTomaso] Pantera Tach Shows 0 at Cold Idle


   Hi Mike,

   I've been having a similar problem with my tach, although, I've never
   tried the the window switch trick.  When my car sits idle for a long
   period I find that my tach stops working until I drive it for a few
   minutes or if it gets a chance to really warm up.  I haven't solved the
   problem yet, but I suspect that it is the tach adapter that was
   installed when the engine was totally redone and I changed over to the
   FAST EZ 2.0 EFI and a mallory ignition system.  I never had any
   problems with my tach until the adapter was added to the system.  Are
   you using an adapter as well?

   Dennis


   [cid:image002.png at 01D6DE89.F5A25270]

   On Tuesday, December 29, 2020 Mike Reilly <reillyms at live.com<mailto:reillyms at live.com>> wrote:

     Hi all.  I've been having a weird tach problem for a few months now.

     When I cold start the car the tach sits at zero but will respond when
   I

     give it gas and go to 2000 RPMs for example.  When I let off the gas
   it

     goes back to zero yet the car is idling fine at around 900 RPMs.  Now

     when I push up on both window switches then the tach will respond and

     read at idle speed but when I let go of the window switches the tach

     goes back to zero.  However, once the car is warmed up then the tach

     works fine and shows idle speed etc. without ever going down to zero

     unless the motor is turned off.  If I restart the car when warm the

     tack works fine.  I think somehow I'm not getting enough voltage to
   the

     tack when the car is cold.



     Videos of the problem:

       * Cold start and playing with the windows (you can hear me
   describing

         what I'm doing near the end of this video)

         ([1][4]https://youtu.be/yIFtsp0ljzk<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FyIFtsp0ljzk&data=04%7C01%7C%7C74fcd405483b438209c808d8acfbecec%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637449545299963469%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ghHU7fL0z2%2Fna8BKgvsg3Sqm0z7gew0hbJY5nf88FGk%3D&reserved=0>)

       * Example of revving the motor when cold

         ([2][5]https://youtu.be/kWaRfGfj2HU<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FkWaRfGfj2HU&data=04%7C01%7C%7C74fcd405483b438209c808d8acfbecec%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637449545299963469%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=IwrzVT8csgMg45VdFkxKheRlr2n73P5qXvqWfe6BE9Q%3D&reserved=0>)

       * Warm running and every thing works fine

         ([3][6]https://youtu.be/X1RY4VwmSmA<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FX1RY4VwmSmA&data=04%7C01%7C%7C74fcd405483b438209c808d8acfbecec%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637449545299973467%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=A0y9DZKsg5loKYs%2FNKZ1aT0ilB65F6LFGTN4tiLmhHQ%3D&reserved=0>)



     Jon Haas rebuilt my tach as I thought that might have been the
   problem

     but it was doing this behavior both before and after Jon's rebuild.

     (By the way he does great work on rebuilds and found some cracked

     resistors in my tach that were about to fail).  I also converted to
   his

     new alternator to replace my stock rebuilt alternator thinking that

     would be the issue but the tach idle problem remained.  This new

     alternator has a built in voltage regulator.



     I measured the various voltages coming to the tach and per my comms

     with Jon these are correct voltages when the engine is running:

       * Voltage at the tach (+terminal) light blue wire = 14.84V

       * Voltage at the +coil wire = 14V

       * Voltage at the +Duraspark = 14V



     My Pantera is #7366 and is a 74L running a DuraSpark electronic

     ignition.  My battery is strong, new and kept on a trickle charger



     Any ideas as to why when the motor is cold the tach won't register at

     idle speed but does once the car is at operating temp?  It's also

     strange that it will come back to life when cold if I push up on both

     window switches when the windows are already closed thus adding some

     load to the car's electrical circuit.



     Thanks, Mike Reilly


   References


     1. [7]https://youtu.be/yIFtsp0ljzk<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FyIFtsp0ljzk&data=04%7C01%7C%7C74fcd405483b438209c808d8acfbecec%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637449545299973467%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=6jDlTwX6MdbLvFpjbp%2BtZxBDEMKG1LAHvw1ZlcZnY10%3D&reserved=0>

     2. [8]https://youtu.be/kWaRfGfj2HU<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FkWaRfGfj2HU&data=04%7C01%7C%7C74fcd405483b438209c808d8acfbecec%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637449545299983460%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=qOwnEhPdtqR4EcdMJlDN1nzzoY8ht0JsfVshpliRpZY%3D&reserved=0>

     3. [9]https://youtu.be/X1RY4VwmSmA<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FX1RY4VwmSmA&data=04%7C01%7C%7C74fcd405483b438209c808d8acfbecec%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637449545299993455%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=%2BS%2BTrlUJHl73Hij8gkfpoW1iQEF%2FnfqSraGonMEFhqc%3D&reserved=0>

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-------------- next part --------------
   Hi Doug.  I made the tach ground the same place Jon Haas instructed to
   ground the ICS board which was a dashboard mounting screw to the metal
   body structure.  I'll have to try your suggestion of using a long lead
   to the battery (-) terminal to ensure a solid ground for testing the
   situation : )   Thanks, Mike


   From: [1]Doug Braun
   Sent: Wednesday, December 30, 2020 11:48 AM
   To: [2]Mike Reilly
   Cc: [3]dennis617 at aol.com; [4]DeTomaso at server.detomasolist.com
   Subject: Re: [DeTomaso] Pantera Tach Shows 0 at Cold Idle


   Mike,


   I see that you tried a second tach ground already but where did you
   make your connections?

   I recommend you have a helper touch one end of a wire directly to the
   battery's (-) terminal while you touch the other end to the tach's
   case.


   Doug Braun

   blue 73L #5505


   On Wed, Dec 30, 2020 at 8:58 AM Mike Reilly <[5]reillyms at live.com>
   wrote:

      Hi all.  Thanks for the input.  I suspect a ground issue somewhere
   in
      the circuit which I'll try to run down.  Although I did try giving
   the
      tach it's own ground wire but that didn't change the behavior.  I
   did
      install a new fuse box and ignition switch controller (ISC) from Jon
      Haas so I may have caused some grounding issue as I moved wires
      around.  I did trouble shoot with Jon months ago but all his
   products
      seemed to be working as designed.  It was doing this before I switch
   to
      the new fuse box.  I was hoping the new fuse box would help.  It
   hadn't
      done it before the ISC was installed but I also had a no start issue
      then due to a bad ignition switch.  So I was touching lots of wiring
      then.
      I'll have some detective work to do here and may need to trace the
      circuit and check everything as folks have suggested.  I'll probably
      reach out to Jon for any further suggestions as well.  Fun with
   decades
      old wiring : )
      Dennis, I have a DuraSpark distributor and electronic ignition
   system
      that's been in the car since 1992 and it didn't require a tach
      adaptor.  I only recently had this problem come up so I don't think
      it's my ignition system : (
      Thanks, Mike
      From: [1][6]dennis617 at aol.com
      Sent: Wednesday, December 30, 2020 6:44 AM
      To: [2][7]reillyms at live.com; [3][8]detomaso at server.detomasolist.com
      Subject: RE: [DeTomaso] Pantera Tach Shows 0 at Cold Idle
      Hi Mike,
      I've been having a similar problem with my tach, although, I've
   never
      tried the the window switch trick.  When my car sits idle for a long
      period I find that my tach stops working until I drive it for a few
      minutes or if it gets a chance to really warm up.  I haven't solved
   the
      problem yet, but I suspect that it is the tach adapter that was
      installed when the engine was totally redone and I changed over to
   the
      FAST EZ 2.0 EFI and a mallory ignition system.  I never had any
      problems with my tach until the adapter was added to the system.
   Are
      you using an adapter as well?
      Dennis
      [cid:image002.png at 01D6DE89.F5A25270]
      On Tuesday, December 29, 2020 Mike Reilly <[9]reillyms at live.com>
   wrote:
        Hi all.  I've been having a weird tach problem for a few months
   now.
        When I cold start the car the tach sits at zero but will respond
   when
      I
        give it gas and go to 2000 RPMs for example.  When I let off the
   gas
      it
        goes back to zero yet the car is idling fine at around 900 RPMs.
   Now
        when I push up on both window switches then the tach will respond
   and
        read at idle speed but when I let go of the window switches the
   tach
        goes back to zero.  However, once the car is warmed up then the
   tach
        works fine and shows idle speed etc. without ever going down to
   zero
        unless the motor is turned off.  If I restart the car when warm
   the
        tack works fine.  I think somehow I'm not getting enough voltage
   to
      the
        tack when the car is cold.
        Videos of the problem:
          * Cold start and playing with the windows (you can hear me
      describing
            what I'm doing near the end of this video)
            ([1][4][10]https://youtu.be/yIFtsp0ljzk)
          * Example of revving the motor when cold
            ([2][5][11]https://youtu.be/kWaRfGfj2HU)
          * Warm running and every thing works fine
            ([3][6][12]https://youtu.be/X1RY4VwmSmA)
        Jon Haas rebuilt my tach as I thought that might have been the
      problem
        but it was doing this behavior both before and after Jon's
   rebuild.
        (By the way he does great work on rebuilds and found some cracked
        resistors in my tach that were about to fail).  I also converted
   to
      his
        new alternator to replace my stock rebuilt alternator thinking
   that
        would be the issue but the tach idle problem remained.  This new
        alternator has a built in voltage regulator.
        I measured the various voltages coming to the tach and per my
   comms
        with Jon these are correct voltages when the engine is running:
          * Voltage at the tach (+terminal) light blue wire = 14.84V
          * Voltage at the +coil wire = 14V
          * Voltage at the +Duraspark = 14V
        My Pantera is #7366 and is a 74L running a DuraSpark electronic
        ignition.  My battery is strong, new and kept on a trickle charger
        Any ideas as to why when the motor is cold the tach won't register
   at
        idle speed but does once the car is at operating temp?  It's also
        strange that it will come back to life when cold if I push up on
   both
        window switches when the windows are already closed thus adding
   some
        load to the car's electrical circuit.
        Thanks, Mike Reilly
      References
        1. [7][13]https://youtu.be/yIFtsp0ljzk
        2. [8][14]https://youtu.be/kWaRfGfj2HU
        3. [9][15]https://youtu.be/X1RY4VwmSmA
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   References
      1. mailto:[18]dennis617 at aol.com
      2. mailto:[19]reillyms at live.com
      3. mailto:[20]detomaso at server.detomasolist.com
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References

   1. mailto:doug351c at gmail.com
   2. mailto:reillyms at live.com
   3. mailto:dennis617 at aol.com
   4. mailto:DeTomaso at server.detomasolist.com
   5. mailto:reillyms at live.com
   6. mailto:dennis617 at aol.com
   7. mailto:reillyms at live.com
   8. mailto:detomaso at server.detomasolist.com
   9. mailto:reillyms at live.com
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