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Drac module pinout

79bonanza

79bonanza

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Well I've been driving my 91 K5 I swapped a 5.3L and 4L60e into for awhile now. All the gauges work except for the speedometer because mines all electronic. Well me not caring I figured I'd just play it by ear and drive slow. Well tonight coming home from work I got pulled over doing 89 on the highway with the converter locked just cruising.

Didn't realize it'd ride that smooth that fast lol luckily the cop was a car guy and let me off with a warning sense no one else was on the road at the time.

But does anyone have a pinout or a pic of a drac module in a 91 K5
 
Okay thanks man, just to make sure I do this right. I'm trying to get the speedometer input from my 5.3 to work the 91 gauge. Do I need to do this to calibrate the speedometer or can I just hook the speedometer input into the drac where the factory tbi went.
 
Do a search on my user name and you should find a pinout as I installed an electric speedo and DRAC in my 89 blazer a few years ago.
 
Your 91 does not need a DRAC with a 5.3L. The PCM has one built in. When you swapped the engine in you should have taken the wires that run from the VSS to the DRAC and hooked them up to the PCM instead to provide it's speed signal. You cannot share the VSS signal between both the PCM and the old DRAC or you'll have issues.

You need to take pin 50 of the red connector in an 99-02 or pin 50 of the green connector in an 03-07 and hook it up to a 12V ignition source through a 1.5K ohm 1/4 watt resistor. You then need to take a wire and hook it up between the PCM and the resistor and hook it up directly to your speedometer.

Pin 50 is a 4000 ground pulse per mile signal derived from the 40 pulse per driveshaft rotation speed signal on the rear driveshaft. Your speedometer uses a 4000 12V pulse per mile signal from the stock DRAC. The resistor you install is called a pull up resistor. When the PCM has the ground turned off the speedometer will see 12V through the resistor but when it turns the ground on the speedometer will see 0V make a square wave of the correct voltage and frequency. The value of the resistor really doesn't matter, it is just there to make sure that your PCM doesn't have a flood of unrestricted current pass through it and blow the ground switching circuit.

If you need to tune your speedometer you can do so using EFI Live or whatever tuner / software you used to disable VATS etc.
 
Russell said:
Your 91 does not need a DRAC with a 5.3L. The PCM has one built in. When you swapped the engine in you should have taken the wires that run from the VSS to the DRAC and hooked them up to the PCM instead to provide it's speed signal. You cannot share the VSS signal between both the PCM and the old DRAC or you'll have issues.

You need to take pin 50 of the red connector in an 99-02 or pin 50 of the green connector in an 03-07 and hook it up to a 12V ignition source through a 1.5K ohm 1/4 watt resistor. You then need to take a wire and hook it up between the PCM and the resistor and hook it up directly to your speedometer.

Pin 50 is a 4000 ground pulse per mile signal derived from the 40 pulse per driveshaft rotation speed signal on the rear driveshaft. Your speedometer uses a 4000 12V pulse per mile signal from the stock DRAC. The resistor you install is called a pull up resistor. When the PCM has the ground turned off the speedometer will see 12V through the resistor but when it turns the ground on the speedometer will see 0V make a square wave of the correct voltage and frequency. The value of the resistor really doesn't matter, it is just there to make sure that your PCM doesn't have a flood of unrestricted current pass through it and blow the ground switching circuit.

If you need to tune your speedometer you can do so using EFI Live or whatever tuner / software you used to disable VATS etc.
Click to expand...

Well that's good to know...
 
Ok that's what I was looking for, quick question tho. When I run a keyed 12v source to pin 50 thru a resistor, do I just split off with another wire at that junction and run it to the speedometer? Kinda like a Y junction
 
Yep! But take the wiring off between the resistor and the PCM. If you take it off the otherwise side between the ignition source and the resistor you'll burn your speedometer out
 
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