Cascade Crew

91camaro_rs · Posted: Thu Nov 04, 2010 11:57 am Post subject: how do tachs work

ok so im wondering how my tach works for my car, i know that it has to do with resistance and thats what makes the tach move up and down, but where is the tach getting the signal from? and what wires and connectors are involved, when i replaced my ecm it worked great for 3 weeks and started to go crazy, there has to be a wire that came loose or something

Twilightoptics · Posted: Thu Nov 04, 2010 2:53 pm Post subject:

Ign Power
Ground
Coil Negative

Those are the 3 wires. In the case of your Camaro, power an ground are intigrated into the dash circuit overlay.

So it's just a single wire going to the coil -.

91RSVert · Posted: Fri Nov 05, 2010 4:09 am Post subject:

IIRC, its the white one off the coil too.

The little circuit boards inside the cluster are known for going bad.

chevymad · Posted: Fri Nov 05, 2010 1:43 pm Post subject:

A jumpy tach is also a sign of jumping spark in the ignition secondary.

91camaro_rs · Posted: Fri Nov 05, 2010 2:05 pm Post subject:

Where would I look to make sure that's not the case

chevymad · Posted: Fri Nov 05, 2010 2:19 pm Post subject:

Ignition secondary is any of the high voltage ignition components. Coil, distributor cap, rotor, wires, or spark plugs. Do you have a miss? With the engine running do you hear any clicks or snaps that might be spark jumping? Make sure all the wires are plugged in good and tight. Look for gray marks on the wires where they touch or touch something else. That is a sign of spark jumping out of the wire.

simpson6716 · Posted: Fri Nov 05, 2010 8:09 pm Post subject:

I have a question about tachs. What would make my tach stay at 2500 rpm and then sometimes work? Even with the car off it stays at 2500.

chevymad · Posted: Fri Nov 05, 2010 8:18 pm Post subject:

That sounds like it's probably the tach itself. Like possibly the movement is sticky.

simpson6716 · Posted: Fri Nov 05, 2010 8:33 pm Post subject:

chevymad · Posted: Fri Nov 05, 2010 8:46 pm Post subject:

As stated earlier, there's only 3 wires making a tach work. One of them comes directly from the coil. The others are power and ground. Break any of them and the tach won't work. But I still think its actually in your gauge.

You might try pulling your instrument cluster and making sure that the plug in is clean and making good connection.

91camaro_rs · Posted: Sat Nov 06, 2010 12:33 am Post subject:

Try doing the resistor fix to the tach chip that should fix it unless you already did it, there is a thread on tgo about it

And now that I think about it one of my spark plug wires got burned by the header, maybe its arking somewhere, I think I'm gonna get all new plug wires with for the new motor

And today my tach was actually working below 2k

aaron_sK · Posted: Sat Nov 06, 2010 8:34 am Post subject:

chevymad · Posted: Sat Nov 06, 2010 12:07 pm Post subject:

I've been reading more and more about capacitor failures in all kinds of electronic equipment. This last year I had to go through my Klipsch subwoofer and replace all the caps. Replaced them with military grade components.

Really sounding like planned obsolescence here.

BluFbdy · Posted: Wed Nov 17, 2010 2:03 am Post subject:

91camaro_rs · Posted: Wed Nov 17, 2010 8:07 am Post subject:

mine ended up being the white wire that goes into the coil, it was loose...