How to calibrate a '89 Firebird tachometer
10-21-2016, 07:29 PM
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Car: '89 Firebird
Engine: 7.0L
Transmission: T56
How to calibrate a '89 Firebird tachometer
Anybody know how to change the calibration of a '89 Firebird tachometer? I need to tweak it to read more accurate at high engine speed so I can better judge when to shift.
I had a friend many years ago that calibrated my tachometer on a bench but I have no clue what he did and it isn't reading so accurate in the car.
I had a friend many years ago that calibrated my tachometer on a bench but I have no clue what he did and it isn't reading so accurate in the car.
10-24-2016, 09:26 PM
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Car: 87 Formula/ 00 Xtreme
Engine: TPI 305/ v6
Transmission: struggling t-5/ 4l60E
Axle/Gears: 3.08/ 3.23
Re: How to calibrate a '89 Firebird tachometer
While I can't help your specific issue, the 'birds seemed to share a common tach board with other cars (not the camaro)
This might at least get you on a start ... http://www.edaboard.com/thread197687.html to fixing your issue. I found that on my quest to trying to solve my tach/electrical issue in my 'bird.
This might at least get you on a start ... http://www.edaboard.com/thread197687.html to fixing your issue. I found that on my quest to trying to solve my tach/electrical issue in my 'bird.
10-25-2016, 08:30 AM
#3
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Re: How to calibrate a '89 Firebird tachometer
You have to cut the leads for pins 4 and 10 on the resistor pack
https://www.thirdgen.org/forums/atta...or-network.jpg
Then install a potentiometer 250Kohm across both pins and tune it with a sig gen on a bench
IIRC RPM = (((input in Hz) * 60) / number of cylinders) *2
So for a V8 the table would looks something like this adjust the pot until it is right. I did find on one of my L69 tachs to get more accuracy down low above 5500rpm it suffered. I am wondering if it has something to do with the RC time constant. Probably would not hurt to replace all the caps while you have it apart.
There are three hookups on the back of the tach. +12V , GND and signal. IIRC I used a 12VPP square wave with a 6V DC offset so the peak was the same was Vin
Also good information in the sticky
https://www.thirdgen.org/forums/atta...or-network.jpg
Then install a potentiometer 250Kohm across both pins and tune it with a sig gen on a bench
IIRC RPM = (((input in Hz) * 60) / number of cylinders) *2
So for a V8 the table would looks something like this adjust the pot until it is right. I did find on one of my L69 tachs to get more accuracy down low above 5500rpm it suffered. I am wondering if it has something to do with the RC time constant. Probably would not hurt to replace all the caps while you have it apart.
There are three hookups on the back of the tach. +12V , GND and signal. IIRC I used a 12VPP square wave with a 6V DC offset so the peak was the same was Vin
Code:
RPM Freq 450 30 900 60 1350 90 1800 120 2250 150 2700 180 3150 210 3600 240 4050 270 4500 300 4950 330 5400 360 5850 390 6300 420 6750 450 7200 480 7650 510 8100 540 8550 570 9000 600 9450 630 9900 660 10350 690
10-25-2016, 10:22 PM
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Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: How to calibrate a '89 Firebird tachometer
Interesting you should say that. My tach is very accurate at normal driving speeds but is running low at higher rpms. It is about 600 rpm off at 7000 rpm. I thought I would just change it to favor accuracy up high but maybe there is a better way.
Frankly, I'd rather just have a Speedhut tach but I think it will stick out like a sore thumb at night when the lighting doesn't match other gauges.
10-26-2016, 09:19 PM
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10-29-2016, 11:04 PM
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Re: How to calibrate a '89 Firebird tachometer
Unfortunately I dont have a good pic of my 84 but it is exactly like the ones in that thread. Must be a pre electric thing
