U need

Some pre info for Impala people: Converting OBD-II to OBD-I So, you've got a 1996 Impala SS, but you don't want to pay for an OBD-II programming package? Well, read on. For the most part, you can remove your OBD-II PCM and simply replace it with an OBD-I PCM. The pinouts are the same, and the OBD-I PCM will just ignore the various OBD-II-only sensors. There are a few differences, though, but fortunately they're easy to fix. First, the '96 cars got 2 higher-impedance (100 kohm) knock sensors, each with their own seperate inputs to the PCM. OBD-I PCMs will "look" for parallel lower-impedance (3.9 kohm) sensors which share a PCM input. You can either replace your knock sensors with the older sensors, or just fool the PCM into seeing the correct resistance. The knock sensor inputs are pins 21 and 22 on the Blue connector of the PCM. Simply bridge these pins together if you're going to use the older, lower-impedance sensors. If you want to keep your current sensors, bridge the pins together, and then place a 2 kohm resistor between the pins and ground (if you're doing this internal to the PCM, there's a very large area of ground plane around the connector). Second, '96 Impala SS received a tachometer that doesn't work properly with the OBD-I PCM tach output. For whatever reason, the tach is looking for one tach pulse for every two spark events, while the PCM provides a tach pulse every time the plugs fires. This means that the tach will read twice the engine speed unless modifications are performed. I built a tach-correction circuit that corrects the signal coming from the PCM. While my circuit is currently placed in the wiring harness (there's a small black box that sits under the hood), my next version of the circuit will sit in the PCM. As I further develop this circuit, I'll post the information here. No other wiring is required. Overall, I prefer this solution (especially since the OBD-II PCMs are more sensitive to "extreme" engine modifications). The real drawback to using OBD-I PCMs is in programming for shift points - the OBD-II computers are much more accurate at shifting the transmission at the correct vehicle speed (apparently, the OBD-II PCM has a much-faster bus speed, which allows the PCM to read the vehicle speed sensor more often). For all but the wildest vehicles, this isn't a problem if the PCM shift points are set to 3-4 MPH under the desired shift point.
U need: -ODB1 PCM -8mm or 5/16ths socket driver -8mm or 5/16ths wrench -1/4 socket driver -flat head screwdriver -soldering iron and solder -electrical tape -cutters -medicine bottle for to hold parts -a well lit work space -2x 1K ohm resistors Radio shack part -4x alligator clips
-Break loose the screws with the 8mm or 5/16ths wrench -Unscrew the the case with 8mm or 5/16ths socket driver -put your parts in the medicine bottle for safe keeping -Use a flat head screwdriver to pry the case apart. It should be kinda sticky the first time :-)
-flip over the orange gasket -unscrew the two screws on the gasket side with the 1/4 socket driver -put your parts in the medicine bottle for safe keeping
-pull the board strait up form the metal case -flip it over -inspect it for corrosion, and burnt parts (just because)

you will be working on pins 21 and 22 of the blue connector -locate pins 21 and 22 on the blue connector *you will find the pins numbered on the inside if you have good eyes and good light -place an alligator over these pins as heat sinks
-pins 21 and 22 show up on the other side of the board -locate the solder joints you will be working on
Mike Licht wrote: > > We prefer a plug and play method. The 96 up knock sensor is a 100 ohm > unit. the 95 back units measure 3900 ohms. The 94/95 pcm looks for > the 3900 ohms. Open the pcm ans solder in a 3.9K resistor from D22 > (blue connector) to ground. This will allow the early pcm to work with > the late KS and allow easy swaping back and forth of the computers. > Much easier than swaping knock sensors. > Mike Licht Those of you considering an OBDII to OBDI swap, please note that the specific fix Mike outlined above only works for an F-car conversion. The B-cars have two knock sensors and require you to jumper pins D21 and D22 together as well as provide a 2k ohm resistor to ground (its actually 1.95k due to the two 3.9k ohm knock sensors being in parallel, but the window of passing values in the PCM is fairly wide). -Scott
-get two 1 Ohm resistors from the package -tightly twist the ends of them together to make a V the are not polarized so it doesn't matter the direction -measure the impedance with an multimeter should measure from 2.1 to 1.9 Ohms (for B-bodies should be approximately 4K Ohms)

take one end of your resister network and bend a long U in it. Use small needle nosed pliers custom fit your connection to 21 &22 -put and alligator clip on the metal lead to absorb heat just above were your going to solder -heat the resistor lead a little with the hot soldering iron -hold the alligator clip steady so you don't get burned -solder the U shaped lead to 21 and 22 -hold the alligator clip steady as the connections cools
-take the other end of your resister network and bend a long U in it. Use small needle nosed pliers custom fit your ground connection -put and alligator clip on the metal lead to absorb heat just above were your going to solder -heat the resistor lead a little with the hot soldering iron -hold the alligator clip steady so you don't get burned -solder the U shaped lead to 21 and 22 -hold the alligator clip steady as the connections cools
-make sure the resistor network is not touching the board -Use the multi meter to check the fallowing A. no connection from pins 23 to 22 B. no connection from pins 20 to 21 C. no resistance from 21 to 22 D. 2.1 to1.9 Ohms form pins 21& 22 to ground (for B-bodies this should be approximately 4K Ohms) -cover the resistor network in electrical tape
-reassemble case and install in car for test :-)
Eric Bryant's 96 SS tach conversion circuit