Bouncing Tach Needle. What the hell..

Islndub · Samba Member Joined: July 06, 2003 Posts: 67

Hi,

I just wantend to know if anyone has this problem and if there is a fix to it. I have a 5 Inch autometer Tach and when I cruise down the freeway at steady speeds 60, 65 mph the Tach needle starts jumping from 2500 to 3300 back and forth. its the bouncing you get when an engine sputters if you know what I mean . in my case my engine is running fine. I'm not sure if this will help but I have an electronic ignition.

I had my timing checked and its fine.
replaced spark plug and wires.
replace cap and rotor.

Thanks

beetleboy58 · Samba Conquestador Joined: February 27, 2006 Posts: 1073

The tach probably has a bad ground.Sometimes if your charging system(regulator) is not working right it makes the tach do that.

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

It may be vibration causing intermittent connections.. does it happen at those RPMs in other gears, like 2nd or 3rd? Could also try installing a diode to see if that filters noise out and smooths the needle.

Rowroy · Posted: Thu Jun 07, 2007 12:43 pm Post subject:

Check for a bad ground. Do you have the same problem at idle?
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nc68bugman · Posted: Thu Jun 07, 2007 1:00 pm Post subject:

Keep tach signal wire away from other ignition wires also. scott

cal63look · Posted: Thu Jun 07, 2007 4:38 pm Post subject:

If it has adjustments for 4cyl 6cyl 8cyl, make sure thats set correctly

k29349@yahoo · Posted: Thu Jun 07, 2007 4:50 pm Post subject:

Had one do the same thing. Not in a VW. It ended up being a bad plug wire.

77charger · Samba Member Joined: November 12, 2005 Posts: 1492

I had the same prob in buggy it has a compufire module.Well after it wouldnt start after i turned it off i said F this i was going to put the points back in get the allen wrench out to loosen module and it was loose so i tightened it back up and problem solved no more bouncy tach.

BTW sometimes the tach would work fine than all of a sudden go crazy hope thats your prob too at least

jimmynotch · Posted: Thu Jun 07, 2007 6:29 pm Post subject:

I have a similar issue with my tach. I just put in a new coil and stock dizzy in my notch. Now my tach needle bounces all over the place and reads way too high. For instance, at idle it reads at about 1500 RPMs (its at 900-1000 and at around 35 MPH, it was reading 5500 RPMs. How do I fix this?
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Jim in Sacto -

dog_jr911 · Posted: Thu Jun 07, 2007 6:51 pm Post subject:

diode
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Lag_Smurf · Samba Member Joined: June 20, 2006 Posts: 287

my tach was doing that right be for my MSD box went out and lost my electronic ignition. I dont know witch one felled 1st.

lostinbaja · Posted: Thu Jun 07, 2007 7:25 pm Post subject:

Make sure the connection to the coil is tight and clean.
Jerry...

jimmynotch · Posted: Thu Jun 07, 2007 8:54 pm Post subject:

Where do I put the diode? Knowing next to nothing about them other than they operate like a check valve for current, how do I install one?

The connction at the coil is sound, as are the connections at the bacck of the tach itself. Something of interst however... when I first noticed my coil was failing, the tach read fine and the needle didn't bounce. But with the new coil, all has gone to sh!t. Am I to assume that bad coil = working tach?
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Jim in Sacto -

Islndub · Samba Member Joined: July 06, 2003 Posts: 67

Rowroy,

at idle its fine, just at crusing speed it bounces.

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

You put it inline on the tach wire.. close to the tach is best IMO. Any of the small radio shack rectifiers should work. Silver band on the tach side of the wire.

Islndub · Samba Member Joined: July 06, 2003 Posts: 67

Another thing folks, when I turn off the engine the Tach needle sits at 1 and when I turn the key on it sets back to zero.

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

It's a floating needle. That's normal on AutoMeters.

Farfromstock

my autometer was doing something similar. when i revved it to the shift point it would go up to 10,000 then drop to 0 then back to what it was ideling at? very little use but i think atm is sell bad units? try a msd inline filter it might work.

jimmynotch · Posted: Fri Jun 08, 2007 11:28 am Post subject:

FASTERFRED · Posted: Fri Jun 08, 2007 1:45 pm Post subject:

I am running a MSD 5 ignition system....Got to attach the tach to the dizzy output, NOT the coil input or it screws up the tach readings because of the multi spark output from the electronic unit....If you are running some kind of aftermarket ignition system, you may look into where you need to connect the tach to get the proper signal...Mine is VDO...The Best...The Lizard...
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