Designing a new dash need a few ideas (Page 108/108)
jscott1 MAY 22, 05:49 PM

Originally posted by rbell2915:

I doubt this will be read but I believe everything should have an update, so my issues have been resolved. The Fiero aux gauges had to be unplugged to fix the oil pressure gauge, and replacing the gauge cluster fixed the temp gauge problem.

Thanks for the update. Too many of these posts end with no resolution.

BTW - If anyone is interested in a plug and play harness I still make them on request.

rbell2915 FEB 08, 09:01 PM

Ok, this may apply to other dash swaps out there with people running an engine swap using a HEI ignition system (ie: 4.9, carb SBC, etc).

Sympton: tach bounces, or work fine till the higher rpms.

Why: the modern tachs are driven off either the ECM or a DIS system and supplies the tach with a nice clean signal - the older systems such as the HEI have quite a bit of noise on the signal and the 'modern' tach can not deal with this noise.

This circuit should eliminate any noise and send a cleaner square wave to you tach input. Edit: fixed picture

I kind of took the lazy way out by hacking up an old Fiero tach to get the filtering circuit out of it. I also have no ideal if the component values are the same as the above diagram (never cheacked).

Sorry, I didn't have a working digital camera to take pictures as I cut up the board, but you should be able to get an ideal of where I cut it from the pictures.

Front view, the large round hole in the lower right is the input to the tach, the resistor pack (white chip) is part of the one that get removed when doing the V8 tach mod.

Rear view, shows a better ideal of the cut in relation to the traces. The brown wire is ground and the upper yellow wire will feed your tach. The lower yellow one is the input from the distributor.

Anyways, there you have it.

This was posted by Mickey_Moose several years ago here and in this thread but the photos are not loading for me. I need assistance on building and installing that HEI filter, my tach is not reading properly past 3k RPM. In fact, I don't think it'll even go past 3k.

I did sent him an email shortly before this post, but it's a long shot if he replies. Haven't seen him around the forum in awhile.

Here is my Firebird cluster as it sits from my point of view. I'm not happy with it right now, so I'm going to attempt to build a new housing out of foam. I also need a V6 speedometer in order to delete the giant buffer I grabbed from the third gen F-body. That should simplify the wiring and free up some room to work.

[This message has been edited by rbell2915 (edited 02-08-2021).]