Incorrect RPM reading on gauge
Thread Starter
Joined: May 2009
Posts: 4,915
Likes: 41
From: Far West
Car: 1986 Camaro Z28 IROC-Z
Engine: 350 Tuned Port Injection, for now.
Transmission: 700R4
Axle/Gears: Posi - 3.23
Incorrect RPM reading on gauge
Here is my tach issue. I took my 86 IROC Z to a shop. The mech hooked up a Snap On computer in the ALDL port and I read the Idle RPM's at 1,000 on the computer. I looked at the Tach and it read 3,300 RPM's. I couldn't ask the mech to floor it so that I can record at what RPM's the tach would max out at because he too busy. So what approach should I take guyz?
I read the other post relating to the tach and theres good info but I know nothing of electronics. Any help would be much appreciated.
I read the other post relating to the tach and theres good info but I know nothing of electronics. Any help would be much appreciated. 
Supreme Member
Joined: Jan 2006
Posts: 3,341
Likes: 12
From: Mooresville NC
Car: LOWERED ♦ CRIMSON METALFLAKE
Engine: ► 400 KUBES ◄
Transmission: 765R4
Axle/Gears: EATON POSI 4.56
RPM Mayhem
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.
Because you said you no nothing about electronics you could get a book to show you component identification and definitions, and you should practice soldering on a surplus PCB.
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
Happy Racing!
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
I Didn’t Wreck, The Track Moved
.
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.
Because you said you no nothing about electronics you could get a book to show you component identification and definitions, and you should practice soldering on a surplus PCB.
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
Happy Racing!
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
I Didn’t Wreck, The Track Moved
.
Thread Starter
Joined: May 2009
Posts: 4,915
Likes: 41
From: Far West
Car: 1986 Camaro Z28 IROC-Z
Engine: 350 Tuned Port Injection, for now.
Transmission: 700R4
Axle/Gears: Posi - 3.23
Re: Incorrect RPM reading on gauge
Hey thanks NINA. Im familiar with soldering, just not the chips and resistors and such. OK, on 4 and 10, Do I solder the resistor directly to the board with the prongs cut and pulled out of the way on the chip?
Supreme Member
Joined: Jan 2006
Posts: 3,341
Likes: 12
From: Mooresville NC
Car: LOWERED ♦ CRIMSON METALFLAKE
Engine: ► 400 KUBES ◄
Transmission: 765R4
Axle/Gears: EATON POSI 4.56
RPM Mayhem
Disconnect pins 4 & 10 before soldering the potentiometer or resistor.
You will be soldering the potentiometer or resistor to the board, not the present resistor network.
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
Happy Racing!
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
I Didn’t Wreck, The Track Moved
.
You will be soldering the potentiometer or resistor to the board, not the present resistor network.
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
Happy Racing!
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
I Didn’t Wreck, The Track Moved
.
Last edited by NINÅ; Apr 20, 2010 at 09:51 AM.
Thread Starter
Joined: May 2009
Posts: 4,915
Likes: 41
From: Far West
Car: 1986 Camaro Z28 IROC-Z
Engine: 350 Tuned Port Injection, for now.
Transmission: 700R4
Axle/Gears: Posi - 3.23
Re: Incorrect RPM reading on gauge
Nice! Thanks NINA. Talk to you later.
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