Is it possible?

-
Clelan

Clelan

Inferno Red Duster
FABO Gold Member
Joined
May 11, 2006
Messages
2,549
Reaction score
3,593
Location
Martensville Sask. Can.
I just changed the tach in my 74 Duster. I went from a cheap 80s parts store tach to a nice Autometer tach that I got for Father's day from my kids.
Now the car idles smoother both in neutral and in gear, to the point that I will likely turn the idle down a bit because it went from 900 rpm to about 1050 or 1100 rpm. I know grounding out the tach signal kills the engine so it seems reasonable that the tach could mess with spark, especially at lower RPM. Has anyone ever experienced this?

Cley
20210803_121821.jpg
 
Yes. I had an old Sun tach and the car ran like crap when it was connected. Took a while it figure that one out too!
 
89on35s said:
I just changed the tach in my 74 Duster. I went from a cheap 80s parts store tach to a nice Autometer tach that I got for Father's day from my kids.
Now the car idles smoother both in neutral and in gear, to the point that I will likely turn the idle down a bit because it went from 900 rpm to about 1050 or 1100 rpm. I know grounding out the tach signal kills the engine so it seems reasonable that the tach could mess with spark, especially at lower RPM. Has anyone ever experienced this?

Cley
View attachment 1715775266
Click to expand...

Looks like you got two gifts!
 
yep, I've seen faulty wiring and/or charging system effect run too. The amount of voltage that comes out of a ballast resistor to the coil is relative to the amount of voltage going into the resistor. I expect yours is going to run better at any rpm.
 
I like that tach and was considering getting it but in the end I didn't want the numbers staggered like that.
 
I wasn't sure I liked that either but when I grab a shift light for the track, then I think it will be fine.

Cley
 
Understand that a common "switched" or Kettering ignition, which is points, breakerless Mopar, HEI, Ford and a few others and NOT CDI or MSD, The coil NEG is NOT simply "switched 12V" All these systems have a high voltage pulse that can be over a hundred volts on the NEG coil terminal. In fact with a "real" Mopar ECU you can get a marvelous zap off the heat sink/ transistor on the ECU because that is the same as the NEG coil connection

So any circuit hooked to coil NEG that is not "up to snuff" can certainly kill off some or all of the signal
 
Gives me something to think about. My tach acts kinda funny sometimes and the engine does run a bit rougher at lower rpm.
 
You must log in or register to reply here.
-

Back
Top