# Broken tach



## CarFreak427 (Nov 19, 2010)

'03 Altima 2.5S - At idle, the needle sits below zero. When I step on the gas quickly, it spins backwards; not all the way around, but counterclockwise almost past the 7k rpm mark. Any clues?


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## QR25 (Nov 18, 2010)

Ususally if the tach is bouncing about, the sending unit is good, or it is dead. Most cost effective and first priority, get new points and condenser, set point dwell
to specs per manual and check all electrical connections. This cures many
tach bounces.


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## jdg (Aug 27, 2009)

QR25 said:


> Ususally if the tach is bouncing about, the sending unit is good, or it is dead. Most cost effective and first priority, get new points and condenser, set point dwell
> to specs per manual and check all electrical connections. This cures many
> tach bounces.


POINTS???
CONDENSER???
On an '03???
You're kidding right???
About the only thing that's remotely correct about the statements above is to check all electrical connections.

Today's tach's are usually servo-motor or stepper motor driven type units, similar to an Idle Air Control motor or a motor on a CNC machine. They're capable of step-by-step motion controlled by a computer of some type, be it a dedicated I.C. or an output from an MCU.
Your tach spinning backwards is indicative of a single broken connection (if it's a servo-motor type), or possibly something as simple as gunk on the needle's shaft (in the case of a stepper motor).
Or, quite frankly, it could be one of a hundred other things. Most likely, if it's not a bad wire from the ECU, it's a bad tach head and will probably have to be swapped out.


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## QR25 (Nov 18, 2010)

didnt see the year eesh


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## CarFreak427 (Nov 19, 2010)

Here's something strange that just happened for the first time last week. We got a TON of snow and I parked my car outside in the school parking lot. It got down below 10 degrees that day. After school, I turned the car on and the tach worked for about 10 minutes until the car got warm. then it dropped back down to the zero and stayed there. This happened a few more times afterward but never lasted long.


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## jdg (Aug 27, 2009)

Sounds like a crap connection. Take it out and start looking for crud and/or bad connections. Clean 'em out, re-solder bad looking connections, and so on. Basic maintenance practices apply here. Just look for something that doesn't look quite right.


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