Real Time Engineering, Tach board

[Hemi2c]

Hi Guys,
I have recently purchased a reproduction RT-E tach board for my 73 Cuda. Rallye dash

Its not working properly , I have tried to make contact with the company and have had no success. Has any one delt with this company before?

The tach is showing 1500 to 1800rpm at idle and when you rev the engine it moves towards 0rpm?

I have sent emails to the company with no reply!

Can anyone help.

 

[Adam]

From RT ENG, Troubleshooting: If your tachometer does not work after installing the board, do not panic. Each tachometer board was tested at the factory and is known to work. Here are some things you can check:
1) Are all four of the wires securely soldered to the board? You can gently pull on each wire and it should not move.
2) Is the case of the tach grounded? You can try running a wire from the outside of the case to a good ground and see if the tach starts working. You can check from the case to a good ground using a ohmmeter
3) Is the tach itself good? You can put some voltage on the tach to check it, but do not leave it on the tach. We will sometimes poke a 12V wire onto the tach wire very quickly (and quickly pull it off) and see of the tach needle moves. If it does not move the tach itself isbad. If you leave 12V on the tach for more than 1 second or so you could fry the tach. Note that you must have the other meter movement wire grounded when you do this test. It is also possible that you connected the two meter wires up backwards, in which case the tach meter movement will try to move the needle under 0 RPM.
4) Is the point’s signal getting from the coil to the D (distributor) wire? You can use a cheap voltmeter to check continuity from the minus side of the coil to the D (gray) wire on the can. You should see an AC voltage on this pin when the engine is running.
5) Is the tach sending-unit getting +12V when the engine is running? You can use a voltmeter or test light to see if the +12V wire is getting 12V.
6) Is the METER+ wire connected to wire on the front of the tach meter movement? You can check this with an ohmmeter.
7) Is the wire on the meter movement closest to the tach board connected to the hole in the tach board labeled METER-? Note that METER- is also connected to the TACH ground, which is the standoff hole that has tin plating around it. You can check continuity between the METER- hole and the case of the tach, and you should get close to zero Ohms.
8) Is the tach sending unit putting out a voltage on the METER+ wire when the motor is running? If it is not putting out a voltage, then it may have a bad ground, it may not be getting +12V, or it may not be getting a good signal from the coil. One other possibility is that the tachometer wire could be grounded or the tach is shorted out. The tach sending unit should put out voltages similar to this when the engine is running: Tach voltage versus tach reading Voltage Tach Reading in RPM 0-0.5 0 0.885 1000 1.4 2000 1.9 3000 3 4000 3.9 5000

http://rt-eng.com/rte/images/c/c7/TachManual67-74_REV13.pdf

 

[Hemi2c]

Hi Adam,
Please see following emails I sent to Greg.

I recently received a M5 Tach pc board and IVR3 from RT-eng for my 73 Cuda. (Rallye Dash)
I followed all the instructions as per the pdf down load from your site.
Double checked everything, calibrated it as per instructions in the engine bay all went well.
I then installed it in the dash cluster and connected it.
I found that at idle the tach reads around 1500/1800rpm, when I accelerate the tach moves towards 0rpm.
I removed it, pulled it apart and checked all connections.
All check ok.

I went through the trouble shooting list,
I have +voltage on the longer silver post.
I have 7.5+ volts on the shorter post. From the coil -ive.
The only thing I have noticed is.
Paper work states that the Meter- hole and the case of the tach should be close to zero Ohms.
I checked mine and it reads 1.8k?
Is this the problem?
I read that if the tach Meter + and - wires are reversed it will cause the tach to read down to 0rpm.
But my connections are correct.

Yellow wire to M+

Black wire to M-

 

[Adam]

So it was working properly when you calibrated it in the engine bay?

 

[Hemi2c]

Well I followed the instructions,

Connect it to battery and using the links calibrated it, so the engine was not on, but it did calibrate correctly.

 

[paulings]

So you have the M5 Tach that has the built in calibration?

 

[Hemi2c]

Yes, the M5.

Anyways found the problem......the old crossed wires in the engine to firewall plug. So the -ive of the coil was going to the ballast resistor instead of going to the ignition box.