FC Tach recalibration for Chevy V8
05-09-05, 11:34 AM
#1
FC Tach recalibration for Chevy V8
I re-calibrated my tachometer Saturday for the chevy small block V8 engine in my FC. I followed the instructions for recalibrating it that are on Granny's site and had only minor problems.
It takes a 12v battery and a battery charger. The charger is suppose to put out a signal that the tach sees. The instructions say to use the cheapest charger available because the more expensive chargers filter the signal out while the cheapo ones do not filter out the signal.
I started with a Chicago dual rate battery charger from Harbor Freight, that has both 6v and 12v settings (12v has 2amp and 6amp settings). After getting it all hooked up, and flipping the power on...nothing. The tach didn't budge or register any change.
I checked the connections, wiring and the current comming from the battery and the charger. Every thing seemed as it should be; both the battery and the charger were outputting 12v. I suspected that the charger might be a "filtered" one, so I went to my shop and got an old charger that I've had for 10 years or more.
After hooking the old charger up, in place of the Chicago charger; the tach jumped right to 3600 rpm, just as it should have.
I turned the adjusting mechanism (potemtiometer?) and tried to dial it back to 1800 rpm (the recommended setting). The adjusting screw bottomed out, allowing the setting to go no lower than 2200 rpm. The instructions said that adding a 1000 ohm resister in parallel would allow the setting to go lower, so I drove to the electronic's store to get the resistor.
I got to the store at 3:03 and read the sign saying they close at 3:00. OK, no problem, there is a Radio Shack on the other end of town. Twenty minutes later and 99 cents poorer, I have the 1K resistor.
Back to the shop to try to figure out which spots on the board to solder the resistor to. It took some careful eyeballing and a tester that beeps when a circuit is closed, to find the right spots on the back of the board.
I fire up the soldering iron and get the resistor soldered to the board. This is the first time I have ever soldered anything to a circuit board and I was a little bit nervous, but it went OK.
One note: be sure to leave the legs of the resistor long enough to relocate it away from the mounting that hold the board onto the back of the tach.
It takes a 12v battery and a battery charger. The charger is suppose to put out a signal that the tach sees. The instructions say to use the cheapest charger available because the more expensive chargers filter the signal out while the cheapo ones do not filter out the signal.
I started with a Chicago dual rate battery charger from Harbor Freight, that has both 6v and 12v settings (12v has 2amp and 6amp settings). After getting it all hooked up, and flipping the power on...nothing. The tach didn't budge or register any change.
I checked the connections, wiring and the current comming from the battery and the charger. Every thing seemed as it should be; both the battery and the charger were outputting 12v. I suspected that the charger might be a "filtered" one, so I went to my shop and got an old charger that I've had for 10 years or more.
After hooking the old charger up, in place of the Chicago charger; the tach jumped right to 3600 rpm, just as it should have.
I turned the adjusting mechanism (potemtiometer?) and tried to dial it back to 1800 rpm (the recommended setting). The adjusting screw bottomed out, allowing the setting to go no lower than 2200 rpm. The instructions said that adding a 1000 ohm resister in parallel would allow the setting to go lower, so I drove to the electronic's store to get the resistor.
I got to the store at 3:03 and read the sign saying they close at 3:00. OK, no problem, there is a Radio Shack on the other end of town. Twenty minutes later and 99 cents poorer, I have the 1K resistor.
Back to the shop to try to figure out which spots on the board to solder the resistor to. It took some careful eyeballing and a tester that beeps when a circuit is closed, to find the right spots on the back of the board.
I fire up the soldering iron and get the resistor soldered to the board. This is the first time I have ever soldered anything to a circuit board and I was a little bit nervous, but it went OK.
One note: be sure to leave the legs of the resistor long enough to relocate it away from the mounting that hold the board onto the back of the tach.
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