TACH Question
Thread Starter
Instructor
Joined: Sep 2001
Posts: 122
Likes: 0
From: Jacksonville Fl
TACH Question
My tach is correct at idle, 800, but seems to be off about 1000 rpm's while driving, indicates 4000 @ 70 mph, engine does not sound like it's turning that...is there a calibration or something I should check?
Thread Starter
Instructor
Joined: Sep 2001
Posts: 122
Likes: 0
From: Jacksonville Fl
Re: TACH Question (Geoff1340)
1977, don't have a clue what the gearing is, TH350 trans. L-48, poopie-canned transducer and ran speedo cable direct. Speedo may not be right on but is ballpark...
Instructor
Joined: Jul 2002
Posts: 132
Likes: 0
From: Little Rock AR
Re: TACH Question (Geoff1340)
The circuit board for the tach may be your problem. I installed a new circuit board and was supposed to reset it using a voltage somehow. I don't remember how to do it, but you may want to ask about it. Mine is definetly off as I run about 1700 rpm at 70 mph with 3.08s
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Re: TACH Question (Geoff1340)
you probably have a bad tach filter...under the hood....or it's missing...
do a search here for the wiring schematic for it....
bet the tach jumps around also....rev engine in neutral watch it jump irratically....
GENE
do a search here for the wiring schematic for it....
bet the tach jumps around also....rev engine in neutral watch it jump irratically....
GENE
Race Director
Joined: Apr 1999
Posts: 15,127
Likes: 476
From: NM
Re: TACH Question (vettinator)
I run about 1700 rpm at 70 mph with 3.08s
tom...
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Le Mans Master
Joined: Dec 2000
Posts: 9,752
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From: Chattanooga TN
St. Jude Donor '08-'09
Re: TACH Question (Geoff1340)
My '79 does the same thing. The circuit is good because I'm running a cheapo aftermarket tach for the time being. It's probably the circuit board. I think you can get them for <$100.
Pro
Joined: Dec 2000
Posts: 560
Likes: 0
From: Camino CA
Re: TACH Question (Geoff1340)
If you have a timing light with a tach connector, you could hook that up and see if it reads the same as the tach in your car. If it doesn't then you have a bad tach or circuit board. If it does read the same, then you may have a bad coil or ignition module.