Calibrating tachometer after 20B swap.

BLK FC3S · 05-05-2008, 12:12 PM

I just had to do this so I did some research, here is the info if someone else has to do this....

After a 20B swap your factory tach will be off. You can either buy a conversion box from MSD or do it yourself. Here's how to do it in a FC. FB and FD's should be similar.

You will need an OLD battery charger, the kind without computer circuitry and all the fancy stuff. Just a plain ol 12v battery charger. 3 small cables with alligator clips. Any wire will work but the clips make it easier. Last A 12v battery. The one in your car works.

First remove your gauge cluster from the dash. Next take the screws out of the circuit board. I wasn't sure which ones I NEEDED to take out so I took em all out. Then pull off circuit board carefully and set aside. Next seperate the clear cover from the gauge holder. Now you should be able to lift off the tach. BE CAREFULL NOT TO TOUCH THE BLACK. It will leave finger prints that are hard to clean off. Grab it by the sides always. On the back should be 4 spade like connections on the top. Reading from left to right should be.. IGN, BUZZER, GND, and SOURCE.
Use the 3 alligator clips now, hook the + of your battery to the ign of the tach. Hook the negative of the battery charger up to your battery on the - side, then hook the alligator clip to the - of the battery as well and to the GND of the tach. Last hook the positive side of the charger up to the Source of the tach. The tach needle will jump up now so keep it positioned about like it will be when it is reinstalled. Mine jumped up to around 4k. Now take the little white round adjuster on the top and adjust it with a small phillips till it reads 2400 rpms. It has a white goop from the factory on the wheel that needs to be broken free to adjust it so be carefull not to force it till that seal is broken. Once its set at 2400 mark it with a magic marker in case it ever needs to be recalibrated. Now its set and should be calibrated for the 20B.
Reinstall everything as it was taken apart. Enjoy a working factory tach again.

My source: http://members.tripod.com/~grannys/rx7tachrecal.html

RETed · 05-08-2008, 05:12 AM

Really don't need to get that messy...
Just crank the adjustment screw all the way over.
For some reason, this comes really close to the 20B tach signal...

-Ted

BLK FC3S · 06-28-2008, 01:38 PM

^ mine was about 1/4 turn away from all the way turned counterclockwise. I dont think they are all the same. Figure the hard part is to get to the adjuster, calibrating it with the charger was the easy part. Might as well check it.

05-05-2008, 12:12 PM	#1
BLK FC3S C088 Join Date: Mar 2008 Location: Mount Dora, FL (no its not a mountian) iTrader: (0) Posts: 112 Rep Power: 17	Calibrating tachometer after 20B swap. I just had to do this so I did some research, here is the info if someone else has to do this.... After a 20B swap your factory tach will be off. You can either buy a conversion box from MSD or do it yourself. Here's how to do it in a FC. FB and FD's should be similar. You will need an OLD battery charger, the kind without computer circuitry and all the fancy stuff. Just a plain ol 12v battery charger. 3 small cables with alligator clips. Any wire will work but the clips make it easier. Last A 12v battery. The one in your car works. First remove your gauge cluster from the dash. Next take the screws out of the circuit board. I wasn't sure which ones I NEEDED to take out so I took em all out. Then pull off circuit board carefully and set aside. Next seperate the clear cover from the gauge holder. Now you should be able to lift off the tach. BE CAREFULL NOT TO TOUCH THE BLACK. It will leave finger prints that are hard to clean off. Grab it by the sides always. On the back should be 4 spade like connections on the top. Reading from left to right should be.. IGN, BUZZER, GND, and SOURCE. Use the 3 alligator clips now, hook the + of your battery to the ign of the tach. Hook the negative of the battery charger up to your battery on the - side, then hook the alligator clip to the - of the battery as well and to the GND of the tach. Last hook the positive side of the charger up to the Source of the tach. The tach needle will jump up now so keep it positioned about like it will be when it is reinstalled. Mine jumped up to around 4k. Now take the little white round adjuster on the top and adjust it with a small phillips till it reads 2400 rpms. It has a white goop from the factory on the wheel that needs to be broken free to adjust it so be carefull not to force it till that seal is broken. Once its set at 2400 mark it with a magic marker in case it ever needs to be recalibrated. Now its set and should be calibrated for the 20B. Reinstall everything as it was taken apart. Enjoy a working factory tach again. My source: http://members.tripod.com/~grannys/rx7tachrecal.html

06-28-2008, 01:38 PM	#3
BLK FC3S C088 Join Date: Mar 2008 Location: Mount Dora, FL (no its not a mountian) iTrader: (0) Posts: 112 Rep Power: 17	^ mine was about 1/4 turn away from all the way turned counterclockwise. I dont think they are all the same. Figure the hard part is to get to the adjuster, calibrating it with the charger was the easy part. Might as well check it. __________________