Speedo and tach issue 1990 iroc
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Junior Member
Joined: Aug 2002
Posts: 31
Likes: 0
From: Vancouver, WA
Speedo and tach issue 1990 iroc
5.0 liter 5 speed iroc. The speedo works sometimes and sometimes it dont. The tach never works. the needle is pegged all the way passed rideline as far as possible and dont move. What can i look to towards a fix?
On the speedo im thinking loose wire possibly or is there still a gear in the tranny that could cause the issue?
On the tach i have no idea where to start looking, just need a lead for this one
thanks guys
On the speedo im thinking loose wire possibly or is there still a gear in the tranny that could cause the issue?
On the tach i have no idea where to start looking, just need a lead for this one
thanks guys
Supreme Member
Joined: Jan 2006
Posts: 3,341
Likes: 10
From: Mooresville NC
Car: LOWERED ♦ CRIMSON METALFLAKE
Engine: ► 400 KUBES ◄
Transmission: 765R4
Axle/Gears: EATON POSI 4.56
Tachy Speedometer
Speedometer:
Check the VSS.
You can monitor the output of the VSS with an audio amplifier to make sure it’s putting out a steady signal.
Connect the amp’s input to the output of the VSS as you would a CD player.
Ground to ground, the signal wire to the inner wire of the audio amplifier wire.
When driving, or simulating VIA having the car on a dyno, you will hear a hum which increases in pitch when the wheels ate turning faster, if the VSS is good.
Tach:
There is circuitry in the dash near the tach.
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 the potentiometer, measure it and install a matching resistor.
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
Happy Racing!
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
If People Drove Any Slower They’d Be Going Backwards
.
Check the VSS.
You can monitor the output of the VSS with an audio amplifier to make sure it’s putting out a steady signal.
Connect the amp’s input to the output of the VSS as you would a CD player.
Ground to ground, the signal wire to the inner wire of the audio amplifier wire.
When driving, or simulating VIA having the car on a dyno, you will hear a hum which increases in pitch when the wheels ate turning faster, if the VSS is good.
Tach:
There is circuitry in the dash near the tach.
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 the potentiometer, measure it and install a matching resistor.
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
Happy Racing!
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
If People Drove Any Slower They’d Be Going Backwards.
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