Tach not reading above 3000
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Tach not reading above 3000
The tach in my 79 has been broken since I bought the car. I found the circuit board to be bad, so I replaced it with one from Willcox.
At first, it read really low, and didn’t read above 1500. I found that the tach filter was bypassed, so I rerouted everything to where it was supposed to be.
Now the tach reads correctly up to 3000. it starts to “trip” at 2500, and bounces between 2500-3000 when I gas it. Could it be a bad filter?
At first, it read really low, and didn’t read above 1500. I found that the tach filter was bypassed, so I rerouted everything to where it was supposed to be.
Now the tach reads correctly up to 3000. it starts to “trip” at 2500, and bounces between 2500-3000 when I gas it. Could it be a bad filter?
Le Mans Master
Joined: Oct 2010
Posts: 6,942
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From: melbourne florida
2023 C3 of the Year Finalist - Modified
I'm sure Willcox will chime in he's great.
My tach stopped working. And I put a Willcox board in and it acted something like you describe. I just gave up on it. I recently put a little bigger cam in the car and to clean up the idle I put a new MSD 6 AL in and the tach started working perfectly. Willcox said I probably had a coil on the way out.cant say that's your issue but mine is working and it wasn't the likely suspect.
My tach stopped working. And I put a Willcox board in and it acted something like you describe. I just gave up on it. I recently put a little bigger cam in the car and to clean up the idle I put a new MSD 6 AL in and the tach started working perfectly. Willcox said I probably had a coil on the way out.cant say that's your issue but mine is working and it wasn't the likely suspect.
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
I'm sure Willcox will chime in he's great.
My tach stopped working. And I put a Willcox board in and it acted something like you describe. I just gave up on it. I recently put a little bigger cam in the car and to clean up the idle I put a new MSD 6 AL in and the tach started working perfectly. Willcox said I probably had a coil on the way out.cant say that's your issue but mine is working and it wasn't the likely suspect.
My tach stopped working. And I put a Willcox board in and it acted something like you describe. I just gave up on it. I recently put a little bigger cam in the car and to clean up the idle I put a new MSD 6 AL in and the tach started working perfectly. Willcox said I probably had a coil on the way out.cant say that's your issue but mine is working and it wasn't the likely suspect.
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Update: tach isnt working at all now, it just sits at 500. Im really struggling to set the zero as well, its got a mind of its own.
Update pt 2: drove around awhile. Tach works up to 3000 for about 20 minutes. Then it starts to droop, and eventually it stops working and holds at 500. After being parked for about 15 minutes, the tach worked again, but for only a few minutes, then drooping again down to 500. The zero set seems to change every time I turn the car off, and occasionally while driving.
Update pt 2: drove around awhile. Tach works up to 3000 for about 20 minutes. Then it starts to droop, and eventually it stops working and holds at 500. After being parked for about 15 minutes, the tach worked again, but for only a few minutes, then drooping again down to 500. The zero set seems to change every time I turn the car off, and occasionally while driving.
Last edited by Cmurray79; May 6, 2020 at 01:40 AM.
Drifting
Joined: Dec 2017
Posts: 1,306
Likes: 226
From: PA
Update: tach isnt working at all now, it just sits at 500. Im really struggling to set the zero as well, its got a mind of its own.
Update pt 2: drove around awhile. Tach works up to 3000 for about 20 minutes. Then it starts to droop, and eventually it stops working and holds at 500. After being parked for about 15 minutes, the tach worked again, but for only a few minutes, then drooping again down to 500. The zero set seems to change every time I turn the car off, and occasionally while driving.
Update pt 2: drove around awhile. Tach works up to 3000 for about 20 minutes. Then it starts to droop, and eventually it stops working and holds at 500. After being parked for about 15 minutes, the tach worked again, but for only a few minutes, then drooping again down to 500. The zero set seems to change every time I turn the car off, and occasionally while driving.
As for putting the filter back in, perhaps it helped directly by filtering you some noise, or perhaps it helped just by unmating and mating the connectors which will clean the surfaces and lower resistance.
Lastly, there are other components in an HEI which degrade with age and like the coil winding are most likely to show this initially at elevated temp. Best test would be with a hand held tach you can hook up. If it gives the same results, then the problem is not the tach. An oscilloscope would also work, not that most people have one. I happen too (don't ask why) and the only useful thing I ever used it for was to verify that my Accel triple spark capacitive discharge module really produced triple sparks.
