E-Bodies.org Cuda Challenger Forum

Does anyone have any experience with Real Time Engineering Tach?  @walt1800 (https://forum.e-bodies.org/mlist/walt1800_245)  has installed one and is having some issues.  Here's what he says is going on....

I recently installed a realtime engineering board in my tach on a 1970 Challenger. The wires are on right for the power and coil wires and I got power from the acc. pin on the fuse box. The problem I'm having is when I turn the key to acc. the tach goes up to around 5 grand. It is still when in the run position until I start the engine and I see it moves but am unsure about it's accuracy as I am just trying to break in a new engine and there were some ignition problems to work out. Any help would be appreciated..


I think this is the one he has... http://rt-eng.com/rte/index.php/67-74_Tach_Board_with_Calibrator_Built_In

Any thoughts?  I'm curious about these too.  I'm thinking of using it and don't know much about it.  I've had really good success with the clock they used to sell.

Quote from: walt1800 on February 26, 2017, 05:47:50 PM
The signal wire is going to the negative side of the coil and I ran a power wire from the ACC pin on the fuse panel. The case must be grounded or the tach wouldn't work at all. It is strange that it does this in the ACC position for sure... like it's getting power to the signal side possibly when in the ACC position.

seems like it is somehow

I think you're on to it.   :yes:   As long as it doesn't hurt the tach it really shouldn't be an issue as you only have the ACC on for a quick moment.

Have you asked Real Time what they thought it might be?

It does seem like it's getting power somehow in the ACC position but it's not a full 12 volts because I believe that would peg the tach. I have sent an email to Greg at Real Time but haven't got a reply as of yet. I don't know if it would make a difference but I noticed the problem while I had the ECM unplugged because I am going to an MSD setup. I wasn't getting any spark and I believe it is because the ECM has died.   

I think you're right about it not getting 12V.  Seems like it's about 5 or 6 volts?  :huh:   Wonder if it's getting the 5 volts from the dash?

Let us know what happens when you plug the new MSD system in.  And I'm curious about what Real Time says they think it is.  I want to buy that board.  How they respond to you and your request for help can have a effect on my decision.

You will not have an issue with the modern circuit / board upgrade , But the Probem maybe the MSD as you have to feed the Tach from the MSD unit NOT the coil

Walt:
 
It is likely your open door buzzer.  Disconnect it and see if the tach goes back to zero.
 
We made a change a long time ago to fix this, but maybe your car has it really bad or you have a really old tach board?   If this is the problem, perhaps my partner can offer some suggestions on how to fix it. One thing you could try would be putting a capacitor on the buzzer or get a solid state buzzer....
 
Greg Garner

Here is my reply...
Greg,

Thanks for your reply. As far as I know the car doesn't have a door open buzzer but it does have a key n buzzer. Although it would be nice to keep the buzzer as a reminder. It works with the door open or closed. I will try to disconnect it and see if the problem goes away. I don't know when the board was built but I bought it this winter when I rebuilt the dash.

As a side note.... I have not wired in the MSD unit yet. This problem is with the standard wiring. I don't know if it will go away with the MSD unit wired in.

Also found this on another site...might be a problem.


My '70 has the buzzer. I liked it but it developed a fault. I believe the relay has a diode to prevent backfeed of current to the rest of the electrical system with key off. Anyhow, it failed and it was passing a small current back to the EFI ECU. The ECU didn't know if it was off or on and went to fault mode. No start. Once I figured this out the buzzer was disconnected. Starting is more important than the buzzer. On an OE system, a fault like that would probably drain the battery.

Boy, that would make sense if it was something to do with the Key In buzzer switch.  That goes off when you go to the RUN position.  The buzzer is located over by the passenger side door just under the dash.  Lots of people disconnect it (if it's still working).  Many stopped working a long time ago.  See if you car has the buzzer hooked up (even if it's not working).

Yes its hooked up and working. I also could be something to do with the door jam switches. They have been replaced and they are not correct for a Challenger. Does anyone have pictures of what is correct for both sides. I hear the drivers side is a three prong and the pass side is a two prong...any ideas? These could be feeding back through the system at a lower voltage. 

Update...I disconnected the key buzzer and the problem is gone. The tach doesn't move when in the ACC position. Still don't know about the door jam switches and if they are causing a problem...but one down!

@walt1800 (https://forum.e-bodies.org/mlist/walt1800_245)  I'm thinking it's a ground thing.  The door buzzer on the underside of the dash on the passenger side needs to be grounded to work.  So when you disconnect the wire you separate that ground and for some reason it makes the tach work.  There are some wires on the back of the tach that needs to be separated with a small fiber washer.  Take a look at these photos....

https://forum.e-bodies.org/electrical-and-audio/11/engine-wont-fire-when-tach-wire-hooked-to-coil/589/

Just trying to help find the reason why it's doing it.   :thinking:

Quote from: walt1800 on February 27, 2017, 08:23:09 AM
Update...I disconnected the key buzzer and the problem is gone. The tach doesn't move when in the ACC position. Still don't know about the door jam switches and if they are causing a problem...but one down!

You will use the grey wire from the MSD unit, if you have any issues with it you may have to get the MSD adapter for older tachs.

Quote from: walt1800 on February 27, 2017, 06:51:19 AM
As a side note.... I have not wired in the MSD unit yet. This problem is with the standard wiring. I don't know if it will go away with the MSD unit wired in.

Im running this tach kit in my car, on the tach signal from my msd ,  if you want to compare  between working and not working PM me i check whatever you need ,  mines in my car but im pretty flexable for a fat guy...

 :haha: :haha: :haha:

Quote from: lulurocks(Ken) on February 27, 2017, 01:03:22 PM
... but im pretty flexable for a fat guy...

Hi thanks. I haven't installed the MSD box yet but I did check the two posts on the tach and I seem to have continuity to ground on both posts. This seems like it isn't right. It is a bit difficult getting to them under the dash though.

I installed the M5 board and don't have these issues. It stays at zero in both ACC and on position. I also have the original buzzer that works.

Let me know if I can look at anything for ya. Not sure if this is relevant but I also installed their voltage limiter.

Edit: oh and I'm running stock dual point

Quote from: walt1800 on February 27, 2017, 04:24:04 PM
Hi thanks. I haven't installed the MSD box yet but I did check the two posts on the tach and I seem to have continuity to ground on both posts. This seems like it isn't right. It is a bit difficult getting to them under the dash though.(https://forum.e-bodies.org/proxy.php?request=http%3A%2F%2Fi1360.photobucket.com%2Falbums%2Fr644%2Fwillyischeap%2Fimage_zpsiowbytvg.jpeg&hash=9fc9da2ad5913e35ea5cd98bd4e2f355eea0aca2) (http://s1360.photobucket.com/user/willyischeap/media/image_zpsiowbytvg.jpeg.html)

Well the fat guy  got the following info:

like aar1064 said my tach stays on zero thru acc and on

My tach , with wires off , did not ! have continuity to ground  on tach power tab  (pink in my pic) or tach coil signal tab  (white in my pic). I did have  a small amount of resitance  but not a dead short.. I couldnt read the meter  upsidedown lol.  But it did not tone for dead short.


And your 5vdc limiter is not part of the circuit its for the other gauges (fuel,oil,temp)

Have you run a 12vdc + wire unswitched from the battery to the tach 12vdc+  tab  to segregate any. Back feed from other devices ?    So. Just 12vdc+ feed    and tach coil wire.