xpndbl3

iTrader: (23)

My autometer Z series tach flutters at idle, until I open the throttle a few hundred rpm then it smooths out. Anyone else have this issue. It's one of the small Z series tachs, under 3" diameter and was $95 new, so not a cheap autogauge one or anything. got a 411 pcm with blue/red harness so it should work easily on the hookup. 5.3L swapped in my 88 suburban.

JMitch19

iTrader: (1)

I assume you are using tach signal from the pcm. If so you need to wire in a pull up circuit. It's really simple. Tap into any 12v ignition power source, put a 680k resistor inline with the wire you just tapped into 12v, and run that wire to the tach signal wire. Tee it into the tach signal wire and you have your pull up circuit. All should be well after that.

xpndbl3

iTrader: (23)

Is that needed when the cold start 800 rpm idle has no flutter at all, only when the idle drops to the 600-ish rpm at warm idle in gear it flutters.

Jeff Smith

iTrader: (44)

I noticed my tach. sometime not accuracy.Thanks I ll do later

gMAG

iTrader: (1)

Here is the method I used. It's the most exacting way to bring up the tach signal.
Thanks once again to "FastKat"-Dave!

http://www.buyrcars.com/jag.htm
Scroll down about 80% toward the bottom of Dave's build.

Tongboy

i've fixed odd tach shutter just by getting a good ground on the tach before - worth trying that before trying to wire in a pull up circuit (not that you might not have to but it's always nice to start simple

xpndbl3

iTrader: (23)

I'll run the ground direct to battery and see if it cleans up the issue or not.

xpndbl3

iTrader: (23)

So did anyone do the 12V power line mod "just" to clear up a flutter at idle, which goes away as soon as your foot brings up the Rpm. Or did it not read correctly throughout the entire RPM range and I'm chasing a possible defective tach or bad ground? Even though it's a good chassis ground that has a few other wires going to it.

sum guy

iTrader: (4)

I did the mod and mine still vibrates. Compared tack to pcm rpm's and its accurate so I let it be.