Stock tach on the 85z.... Got another tach from a member on here. Tach is not the issue as it is doing the same thing the original tach to the car is doing.
Heres what happens. When you turn the ignition to "on" without starting the car
the tach slowly climbs to pegline 7 grand....
Turn the ignition switch off, tach remains at 7 grand.
The oil pressure guage that is w/ the tach is fine.
When you start the car, The tach automatically jumps to 7 grand or peg redline.
Sounds like an electrical short. I realize that I only have to have hot and an ignition to run the tach. My question is, how can I test the factory connection wires at the distributor? There are two wires that go to the distributor, both are marked on the cap. This is the same exact problem I had with the old tachometer.. Its like it has a short in the wire some where I suppose. What can I do? I would really like to get all the factory guages working but its getting less likely each day.

 

The problem is in the circuit inside the dash that moves the pointer.

It’s contained on a small plug-in PCB or integrated in the main board.

On the PCB you’ll see a resistor chip.

Desolder pins 4 & 10.

Use a 500K potentiometer.

Solder it across traces 4 & 10.

Move the potentiometer to half way.

Start the engine and compare the tach reading with a test equipment quality tach.

Dial it in, unsolder one side of the potentiometer, measure it and install a matching resistor.

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Happy Racing!

 

thanks!

 

It'sd possibly a bad Printed Circuit on the back of the speedo cluster. Over the past few years I've noticed more and more bad printed circuits,.... MANY are beginning to "seperate" after 20 + years of service.

 

Thanks....out of the 6 guages... I can only get three to work correct..
The speedo, the oil pressure, and the gas guage......
I think I am going to replace the whole cluster if I can find one cheap enough.
It would be the easiest way for me to do the repair.
Age can be a bugger. I am surprised more have not chimed in with the same or similiar issues.

 

No Problem !

Keep in mind; if you get a replacement cluster than be sure it's not an 82-84 version,...... You will need an 85-89 style or there will be a compatability problem with the 85's dash harness causing a conflict with the E-Brake warning Light and the backlighting.

 

yes, Ill be sure its 85 up..
Thanks!

 

Will there be an issue swapping an 85-89 gauge cluster into an 84 model. None of my idiot lights work anyway. Cause the computer isn't hooked up anymore. Thanks

 

The 85-89 cluster is not directly compatible with the 82-84 dash wiring. The BRAKE warning light was placed in a different location on the cluster and the printed circuit on the back of the cluster was re-engineered as a result. One of the cluster "backlight" bulbs is also effected by this difference.

Mikey; You could probably re-pin the dash connectors, but the easiest way to go is to use a 82-84 gauge cluster if your looking for "plug-&-play" installation.

P.S. The "idiot" lights are not controlled in any way by the ECM. The engine sensors feed the gauges directly to the cluster.

 

Well I didn't know that I thought the idiot lights were controlled by the computer. Sometimes the brake light does light up when I first turn on the key but none of the others come on. Is that a problem with the cluster it's self?

 

my gauges are messed up as well. when i turn on the dash lights my rpm's just peek out. and my gas gauges is on full when i know its not "full" and my temp gauge doesnt work? im thinking its a ground? can anyone help please.

 

The Tach and lighting systems should not be related or dependant on each other in any way. I'd suspect a bad printed circuit in your cluster too.