4 Attachment(s)
Bench interface for OBD1 LT1 PCM
I was running into errors trying to read my PCMs using the cable and a laptop, so I got the idea of using a 12V power supply to power the PCM and then making a short interface harness using GM type connectors so it would plug in. This made my 21 year old unreadable in the car PCM readable. I used Winflash and with a 0 setting on the communication delay it gave me fast results. The attached photos compliment the text, one is my setup before I got the remaining connector parts. I set everything on a small sheet of plywood for portability.
Disclaimer: My first go at this omitted 2/3 of the connector parts as I went by the part number in the shop manual. This was a workable solution, but I had to manually plug/unplug each wire and then seat the connector. I have added the other connector parts based upon research and datasheets. They are currently on order and if they are incompatible I will update this post.
Here's what I did (part numbers are linked where possible):
1. For the 12V power supply, I used an old computer power supply. This page tells you how to do it. I did not bother with the 5V and 3.3V wires. It was a tight squeeze as there were a lot of black and yellow wires.
2. I bought the following parts from Mouser.com. You can buy any of these w/o an account and you do not need to buy minimum quantities. Shipping is very reasonable as well. Note that a connector is the plastic piece(s) while a terminal is the metal part that fits inside a connector:
a) 1x binding post terminals #565-6883. I drilled two pairs of 29/64 holes for these for a second set in case I wanted to have 5 and 3.3V posts later. They mount in pairs. It may be easier to find some single posts, but these were cheap. You can paint the knobs so you know what does what.
b) 4x Delphi 12129025 connectors (part 1 of 3). This is the part that holds the wires. I was initially unaware of the other parts and as able to use this by itself, but it is hard to connect/disconnect this way.
c) Connector retainer locks: 1x 12129021-B (black), 2x 12129022-B (clear), 1x 12129023-B (blue). The red connector is apparently 12129024-B and is a special order. Use a clear one and mark it with a red sharpie marker. These are part 2 of 3 parts for the 32-way connector.
d) 2x Delphi 12129028 strain relief connectors (left exit) and 12129030 (right exit). These are connector part 3 of 3, the gray part that fits over the above parts.
e) 16x Delphi 12084913-L female "Micropack" terminals. These fit into the connectors and the wire fits into them. Always order more than you think you'll need.
f) 2x 1/4" ring terminals for 10-12 gauge wire #19044-0167. These can also be found at a hardware store.
g) 1x OBD connector (16 pin) #12110250. This connector will work for 1995+ cars that use a 16 pin OBD connector. The tuner cable will plug right into it.
h) 8x 12129484-L female terminals for OBD connector.
i) 2x 12160437 connector locks- these hold the terminals in place and are essential.
j) Inline fuse holder #576-913-007 or similar- must be cabaple of 15 amps.
3. I had 18 gauge TXL wire on hand, but it can be found in shorter lengths for reasonable prices at Autosports wiring. Be sure it is AutosportS wiring, as there is a similar site that does not sell wire. The terminals are really small, so you could get by with 20 gauge if need be. You'll need the following:
a) Pink for +12V power. You could use red or orange, anything to show the power feed wiring.
b) Black for ground. You can use a sharpie marker to make a stripe if you want- I used silver where a black/white wire was shown.
c) Tan for data and one ground. I again used a silver sharpie to stripe the tan ground wire.
d) White wire for data ground, you can use a black sharpie to stripe it. I did not have any, so I used a black wire and striped it.
4. Crimping tool- I have a Milbar 25E, these are around $50, or you can look for a Metripack or Weatherpack crimping tool on eBay, I found one for around $32 shipped. If you are careful you can use some small needle nose pliers. This would be the most expensive part of the project. A quality tool will pay for itself in time & trouble saved.
At this point, you have built the power supply and are now ready to build the harness. The following diagram was gleaned from a 1995 GM F-Body (Camaro/Firebird) shop manual. It is essential that you make sure your PCM is properly wired for power, ground, and data. This diagram is known to work for 1995 PCM #16188051.
There are 4 connectors for this PCM, the shop manual calls them A, B, C, and D. They are color-coded, with A=Red, B=Black, C= Clear (sometimes called gray), and D= Blue. There are 32 pins in each connector, and the terminals they use are called Micropack. The pin numbers are visible using a magnifying glass to look at the corners of the connector and run from 1-16 then 17-32 for the second row (see pictures). Be advised the connectors are numbered on the PCM, and one set will be upside down when the ones you are reading are right side up:
Example:
Black
1-----16
17---32
Blue
32---17
16----1
Wiring to A or red connector:
Pin 2: Black/White wire to ground
Pin 18: Tan/white wire to ground (stripe the wire or just use a black wire)
Wiring to B or black connector:
Pin 15: Pink wire to +12V
Pin 30: Pink wire to +12V
Pin 31: Pink wire to +12V
Wiring to C or clear (sometimes called gray) connector:
Pin 32: Black wire to ground
Wiring to D or blue connector:
Pin 1: Black wire to ground
Pin 3: Pink wire to +12V
Pin 20: White wire to data ground
Pin 30: Tan wire to data feed
Wiring the OBD connector:
Pins 4 and 5: Black wire to ground
Pin 6: White data ground wire to blue connector above
Pin 9: Tan data wire to blue connector above
Pin 16: Pink wire to +12V
