Real Time Engineering board Tach, help

[Cuda Cody]

Does anyone have any experience with Real Time Engineering Tach?  @walt1800  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.

[Cuda Cody]

Could it be a bad ground?  Does it go back to 0 when you go from the ACC to the RUN position?

[Cuda Cody]

I have an aftermarket tach on my run stand and once I give the gauge power it does a sweep.  But then it goes back to 0 until I start it.  Is there a chance the 5K in ACC is some sort of factory test / check that it does?

[walt1800]

Yes it goes back to 0 when it's in the run position. In the acc. position it goes to about 5 grand and stays there...not like a sweep.

[Chryco Psycho]

I have installed 3-4 of these & never seen this issue 12v power to the gauges should be the same in run or acc , have you tested the power lead to see if something weird is going on  I assume you have the signal wire to the Negative side of the coil , there is a calibration tool to adjust the tach so  it will read accuratly , just a signal generator but it is needed to set it right , I borrowed one from a friend that did the same conversion .

[Cuda Cody]

If you have the M5 board it looks to be easy to calibrate.  It doesn't sound right if it just sticks at 5K on ACC.  Something is getting not right.... 

Do you have the M5?  Here's the manual...

http://rt-eng.com/rte/images/c/ce/M5tachboard_manual.pdf

[walt1800]

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.   

[walt1800]

Yes it is the M5 for 70 mopar

[Chryco Psycho]

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

[Cuda Cody]

I think you're on to it.      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?

[walt1800]

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.   

[Cuda Cody]

I think you're right about it not getting 12V.  Seems like it's about 5 or 6 volts?     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.

[Chryco Psycho]

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

[walt1800]

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.

[walt1800]

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.