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This page is going to hold a lot of stuff eventually. It is presented in a question and answer format. They may be randomly placed at first, but we'll eventually make some order out of them. Here are the topics covered here: 1. How is the under dash connector wired to the PCM in the OBDI LT1
cars? How is the under dash connector wired to the PCM in the OBDI LT1 cars? This answer is targeted towards folks doing LT1 retrofits (Monte Carlos / Street Rods / El Caminos / S10 Pickups, etc) OK, grab your voltmeter, wire snippers, and soldering iron, we're
gonna have some fun. For the older rectangular 12-pin style, the under dash connector has the following pinout: F E D C B A A = Ground For the OBDII style connector (16-pin D shaped), it has the following pinout: 01 02 03 04 05 06 07 08 05 = Ground (it's also helpful to have 04 = Power Ground and 16 = +12V wired in as well) On to the PCM now. The PCM has the serial data on Blue 30 (D30). This needs to go to "M", "E", or 09, depending on your connector above. It's a tan wire on my 1994 PCM. Mode select needs to go to Blue 20 (D20). It's a White/Black wire on my 1994. ALDL Ground needs to be tied in to Blue 1 (D1). This ground wire actually winds its way through the chassis to get to the PCM, but it wouldn't hurt to run a jumper wire directly to it. The better your ground, the better your ALDL communications reliability. Mode select typically isn't used on our cars for the laptop based scan tools or the LT1_Edit program. It's for diagnostic modes that only the Tech2 will allow. So, it's good to wire up if you think one day you'll hit it with a Tech2, but you don't have to have it wired up. What happens if my PCM halts programming in the middle of a programming sequence with LT1_Edit? It has happened (very rare, but it does), it is a risk we take. LT1_Edit, when programming, erases one flash chip first, programs it, then erases the second flash chip, and then programs the second one. So, if your programming sequence halts during the first 50%, the first chip has been erased and your PCM will not boot (to start the car). If your programming sequence halts during the second 50%, the second chip has been erased and the PCM will not boot. Your PCM is not dead, it can be revivied, but it needs surgery. The erased chip will need to be removed from the PCM board and reprogrammed with an flash chip programmer. I am able and willing to fix PCMs for a small fee as a favor to my customers. Would you like to see what I do? Check out the Flash Fix web page! Granted, my soldering skills are a little better than average, so I don't recommend you try this at home. To make sure your PCM won't lock up, you need to disable ALL power saving features of your computer (both in the laptop BIOS and in Windows), disable the screen saver, make sure all automotive accessories are turned off (A/C, Radio, etc), and make sure your laptop battery is sufficiently charged. And don't crank up your home stereo and play the drums on your steering wheel while programming or reading - that may cause data errors (right LJ?). How do I make a bench top programming setup? Here's another handy tool if you're working with more than one PCM (as I am). Or if your motor is out, but you want to do some PCM work. Cost is under $5 for the harness parts, and about $32 for the power supply (you can use a car battery, but only temporarily, as it will be drained). Very easy to build. First, collect the components. You can get everything from RadioShack.com (hey, I never leave the house anymore to shop!). Now, you can buy these as a whole connector at the store, but if you're doing it over the 'net, here are the part numbers and descriptions: (1) Crimp type cable mount D-sub, 25 pin Female, 910-4770, $.62 / ea
Now, I just tore apart some old equipment that I had laying around, yanked a 15 volt regulated power supply from it, and put two diodes in series to drop the voltage going in to the PCM down to about 14 volts. You need the voltage higher than 12 volts, but lower than 15. So 13.8 regulated is a good target. What you'll need to do is to make a wiring harness using the gold pin sockets. There are four required for the ground (0V) wires, and four required for the hot (+12V) wires. I did them in a daisy chain - strip the end of the wire, crimp and solder a pin on there, cut the wire a few inches up, stripped *both* pieces of wire, crimped and soldered both of those pieces to another socket, and kept going until I'd covered the 4 pins I needed. For the ground wire, I made the first jump from D1 (Blue 1) to C32 (Gray 32), about an 8 inch piece of wire. Next, we jump from C32 to A18 (Red 18) using about 4 inches of wire. Next we loop from A18 to A2 (the adjacent pin) with a loop of about 1.5" of wire. From there, we go to the ground terminal of the power supply. For the +12V wire, my first terminal is at B15 (Black 15). From there, I jump with about 1.5" of wire over to B31 (the adjacent pin), and from there about 1.5" of wire to B30 (right next door!), and then have about a 4 inch piece of wire jumping to D3 (Blue 3). From D3 I jump to the positive terminal of the power supply. Now for the ALDL Interface. You need at least two wires - ground (Pin 1 on my converters), and serial data (Pin 5 on my converter, D30 (Blue 30) on the PCM. You may need to provide 12V, but most converters were shipped with port power option enabled, and all desktops should support the port power option. That clear as mud? ;) Email me if you have any questions! How do I build one of your interfaces? Where's the schematics? See my Assembly Notes Page for all the gory details! That's old stuff, though. Also check out the New Style Converter page, no more jumper wires everywhere! I don't sell them like on the 1/29/00 Page anymore...
Check this diagram out: Meziere Install Schematic (more to be added soon) |
