1227747 to 16197427 Conversion PCM Swap with Wiring Pinout Directions!

[TheApocalyptican]

I am planning on switching from the 7747 to the 7427. Need to the get the PCM itself tho, and since I have a V8, do I need a 7427 from a V8, or will the V6 version work too?

[dave w]

I am planning on switching from the 7747 to the 7427. Need to the get the PCM itself tho, and since I have a V8, do I need a 7427 from a V8, or will the V6 version work too?

I've never tried using a V6 Memcal for a V8 engine. I've done several '7427 conversions, all V8 engines and all had V8 Memcals.

dave w

[dumb_dog]

For those interested I have both the DRAC and VSSB. These little boxes convert a 40 pulse tone ring into the signal to for the PCM or ECM, and speedo. The VSSB has more outputs than the DRAC. Power, ground, and sensor inputs are the same. The PCM 427 with VSSB uses the RWAL singal (anti-lock brake signal), 40 PPR signal, and 2000 PPM signal. The VSSB also converts the 40 pulse tone ring signal to 2000 PPM for the Speedo. The DRAC is missing the 2000 PPM signal to PCM but because i am using a cable driven speedo i can use the 2000 PPM signal from the DRAC as the signal into the PCM by relocating one wire. With the correct diagrams and much research they can be used interchangebly.

As a side note from another question long ago in this thread the VATS pin is pin B7. There is no wire in that location but it is +5 volts and when pulled low at 30Hz the PCM will allow engine start. So enable VATS and use pin B7. I have tested it and activtly using it in my conversion.

[CDeeZ]

I'm interested in what you got there bossman. I used both DRAC and VSSB successfully when I was experimenting with them a year or two ago. I've got a pile of about a dozen of them altogether from various trips to the yard.

If memory serves me correct there are two VSS inputs on the VSSB one for VSS and the other for trans output speed? (Been a while since I looked at this so I can't remember exactly).

[dumb_dog]

You are correct there are two outputs from the VSSB to PCM(s) 6395 or 7427. One is trans output speed at 40 pulses per revolution (PPR) and the other is vehicle speed at 2000 pusles per mile (PPM). The DRAC has the same two signal at different pin locations. So with some repining DRAC and VSSB can be used interchangeably but with the DRAC if you are using an electronic speedo then you will need a VSSB because the DRAC does not have enough outputs for the PCM and speedo. Just FYI the speedo output is at 2000 PPM just like the vehicle speed input to the PCM.

[dumb_dog]

Hopefully these will help clear things up. Attached are the pinouts for a 1992 DRAC and 1994 VSSB. Also attached is a picture of both DRAC (left) and VSSB (right).