Can someone tell me what a Tac filter is, does, and location?

Thanks Roger

 

Can someone who has done a C5 front brake up grade provide me with wheel specs?
What is the width of the interior of the wheel?
What is the offset?
THANKS!!!!!!!!!!!
Roger

 

The tach filter is a condenser looking device with two wire connections. One wire hooks up to the distributor cap connection marked, "Tach", and the other wire plugs into the harness and goes to the I/P. I believe it is mounted to the back of the plenum/intake manifold, on an L98. You can trace the wire from the distributor to locate it. On the L83, it mounts in an intake manifold lid stud. Where ever you find it, it needs to be mounted to a ground. On my car, it appears as though it does nothing. Mine broke and I plugged the harness connection direct to the distributor connection and it works just fine.

RACE ON!!!

 

The tachometer filter is an electronic filter that allows only the fundemental frequency of the pulses coming out of the distributor to get to the circuit in your cluster that displays rpm. Without it, it is possible to get random rpm indications from the tachometer.

 

The C5 upgrade is very easy. The offsets are the same between late C4s and C5s.

What year is your vette?

 

The tach filter is a low pass filter made of two resistors and two capacitors. As far as I can tell the values of the components of the filter are chosen so that noise from the ECM is eliminated. The coil is connected to a switch inside the ECM. This switch will open and close rapidly and in doing so it will bounce and that results in high frequency noise. Any other theories out there?

As the filter gets old the capacitors will start to short to ground (erratic), that will result in "spikes" showed by the tach (common problem). My 91 has a "glued" filter but that does not appear to make them last much longer.

It seems the tach (at least on my 91) itself is doing very "hard" filtering, you notice the slow response when revving the engine. I do not quite understand why the tach itself is not able to do all the filtering required. Perhaps a misstake when designing the tach?

In 92 the ASR is connected to tach wire. If you do not have a filter the ASR might believe that the engine rpm suddenly jumped 1000 rpm due to wheel slip... and then the SA might be decreased, thus loosing power. Or, I got everything backwards...

My 91 filter was, by the way, located on the backside on the "main" cable harness behind the engine. Seems it has moved 90 or 91. Also, it has three wires (a separate ground) and is glued inside a plastic box.