How can a tachometers accuracy be tested?
Thread Starter
Racer
Joined: Dec 2005
Posts: 399
Likes: 0
From: Kearns UT
How can a tachometers accuracy be tested?
I ordered an adjustable shift light made by Proform, but there is a 500 RPM discrepancy between my tach and it. If I set the Proform shift light to come on at 3000, I have to take the tach in my car to 3500 before the light comes on. I have a 78 Silver Aniv Ed with a zz502/502 crate motor and MSD 6AL ignition. Hope this is all that is needed.
Racer
Joined: Jul 2005
Posts: 499
Likes: 1
From: Winnipeg Manitoba
A small A.C. Adapter can be modified for use as a tach tester.
Something with 6-9V DC output will do the trick.
Take it apart, remove the filter capacitor, and replace it with a 1K resistor.
Put a second 1K resistor in series with the output to limit current.
This should give you a 120Hz, full wave rectified signal.
Disconnect the Tach from the distributor, connect the A.C adapter to the tach input. The Tach should read 1800 RPM.
DISCLAIMER
This procedure is simple, and the risk is minimal.
However, I don't know your level of expertise.
My tach tester suggestion involves parts that contain high voltages (120V).
This can kill you.
If your not comfortable with that, then forget what I said.
If you do not fully understand the instructions,
please seek help from someone that does.
Something with 6-9V DC output will do the trick.
Take it apart, remove the filter capacitor, and replace it with a 1K resistor.
Put a second 1K resistor in series with the output to limit current.
This should give you a 120Hz, full wave rectified signal.
Disconnect the Tach from the distributor, connect the A.C adapter to the tach input. The Tach should read 1800 RPM.
DISCLAIMER
This procedure is simple, and the risk is minimal.
However, I don't know your level of expertise.
My tach tester suggestion involves parts that contain high voltages (120V).
This can kill you.
If your not comfortable with that, then forget what I said.
If you do not fully understand the instructions,
please seek help from someone that does.
Thread Starter
Racer
Joined: Dec 2005
Posts: 399
Likes: 0
From: Kearns UT
Ok, here is what I found. I hooked my shift light up in my neighbors mustang and it lit perfectly with his stock tach and Autometer tach/shift light. Now it gets confusing (at least for me).
I have an MSD 6AL ignition box and just for fun I put a 3000 rev limiter chip in and took the car to 3000 RPM's using the stock tach and the engine cut out right at 3000, yet when I set the shift light to 3000, it doesn't light until 3500. I was fully convinced it was my tach, but with the rev limiter chip it cuts out right at 3000, yet my shift light, lights perfectly with my neighbors MSD 6AL and shift light. I'M SO CONFUSED!
Can anyone explain this?
I have an MSD 6AL ignition box and just for fun I put a 3000 rev limiter chip in and took the car to 3000 RPM's using the stock tach and the engine cut out right at 3000, yet when I set the shift light to 3000, it doesn't light until 3500. I was fully convinced it was my tach, but with the rev limiter chip it cuts out right at 3000, yet my shift light, lights perfectly with my neighbors MSD 6AL and shift light. I'M SO CONFUSED!
Can anyone explain this?
