Charger Specailties Tach Problem In 71 Charger

[purple70rt]

We just put a new charger specialties tach in my son's 71 Charger.  Tach jumps in between 1000 and 3000 when idling, and at about 35 mph the tach pegs out. Anyone have problems with these or any suggestions?  Customer helpline was a joke, all I got was we have never heard of that before, send it back and we will check it out (which is good I guess, but it is a pain in the ass to change out).

Made my own harness. Also when the key is off the tach drops about a 1/2 inch below O, when you turn the key on iut goes to 0.

It's driving me crazy!!!!!!

Thanks in advance


Dale

[71_deputy]

try a points type capacitor from the neg of the coil to the engine ground. that sometimes helps to smooth out the pulses to the tach.

John Mac

[purple70rt]

have a capacitor on it, car does have pionts also.  Do you mean run a wire from the neg side of coil to the where the engine is  grounded to the firewall?

[RShastwell]

I know this is and old post but I just installed  this same Tach in a 71 Roadrunner , with the same Problem . 

Did you ever get to the bottom of it ??

I initially figured the Tach was defective , but I have received 3 now , all with the same problem.  I tried the 3 Charger Specialties Tachs in two different cars with the same results . Both cars have factory points ignitions systems .

When I hook a engine analyzer or an old Sun Super Tach II to the wires I ran to the dash both of these work perfectly.

Like you the Tech support line from Year One and Charger Specialties are no help. They just report how many thousand they have sold and say they have never heard of anything like this ..... Year one will send me one a week , but after 3 I doubt

Here's what I've done far in case somebody can think of something I've missed ..


1) Verify 12v only when key is on - Good

2) Verify wire to negative side of coil- Good

3) Tried to ground dash chassis with separate wire - No effect

3) Pulled new Tach and hooked it up with jumper wires outside the car , - Same result as above

3) I have an old engine analyzer ( sears) with a tach function.  Hooked it up to the car as a sanity check , Red to positive battery , Black to negative Battery, Green to negative side of coil.  -Reads perfectly , 1000 at idle steady reading , climes when engine accelerates.

4) Hook engine analyzer up inside the car using wires I ran for new Tach.   Red to new Keyed 12 V wire , Black to metal chassis of dash , Green to new wire that goes to negative side of coil. -Engine analyzer reads perfectly.

5) Determined Tach must be defective , sent it back to Year One and received a new one on Friday .

6 ) Installed new ( Second ) tach --- Same Result .  At idle it reads between 3-4K and very erratic. Slight acceleration , tach reads 6K+

7) Ran through same testing listed above again , just to be sure ? -Same results


Really running out of ideas.

Took second new tach and wired it up to a 69 Z28 I have . I know that should be illegal , but I getting desperate ......  12 v from plus battery to new Tach, Negative side battery to new tach housing , negative side of coil to new tach terminal.---- basically the same result . The Z28 idles lower , maybe around 800 compared to 1000 . New Tach reads about 2200 , rev the motor slightly and it thinks your spinning at 5K plus .


Many Thanks in advance for any assistance !!