SyTy MEMCAL


When people talk about the "chip" or "PROM" in a truck, they are referring to the MEMCAL. The MEMCAL is a T-shaped piece of black or brown plastic with a blue cover. It contains all the data used by the Electronic Control Module (ECM - the "computer") to make your truck run.


Under the blue cover, you'll see two distinct halves. On the right side, there is a computer chip. This is the actual EPROM (Electronically Programmable Read Only Memory) which stores the programming code. Stock chips and this ATR Pitbull use UV-erasable chips. Under the label is a little window. Shining UV light into this window will erase the chip. If the label came off and the chip was exposed to sunlight, it's very possible that it could get erased. Many tuners now use EEPROMs (Electronically Erasable PROMs). These are erased by having the chip burning hardware send a certain voltage to the chip. This is easier, and makes the UV window obsolete.

The programming in the PROM consists of two parts. Part of it is the actual code, and part of it consists of lookup tables. The lookup tables contain all the variable data that is used to tune the truck. This what you're changing when you use Promgrammer. This is the data such as how much fuel to use under certain conditions, minimum temperature to turn on certain features, etc. The code is actually the program that your computer runs. Just like a program on your PC, it tells the computer what to do with the data. To change this part of the programming, you need to use a hex editor and have a very deep understanding of how the program works. Changes were made to the code in order to let the ECM understand the output from the 3-bar MAP sensor instead of the stock 2-bar MAP sensor.


On the left side is the Electronic Spark Control circuitry. There is a raised board with squishy epoxy over it, and some more chips underneath. The ESC listens to the knock sensor and tells the ECM when the engine is knocking. The ESC is tuned to a specific combination of parts, so it will only work in the vehicle it was designed for. The same ECM found in the SyTy was also used in the turbo Sunbird and Quad4 cars. You can remove the ECM from one of those cars and drop it into your SyTy, and it will work exactly the same. However, you'd need to replace the car's MEMCAL with a SyTy MEMCAL. The programming in the chip would not be compatible, and the ESC would be calibrated for a different engine.

The Ultimate chip (and other similar units) contain only a PROM, not the ESC. Because of this, you need to piggyback your stock MEMCAL on the chip's adapter board. Here is a simple diagram of how that setup looks.

                 (Stock chip)
            -------------------
            |   PROM |   ESC  |
            -------------------
                           |
-----------------          |
| Ultimate PROM |          |
-----------------          |
              |            |
              |            |
           -------------------
           |  Adapter board  |
           -------------------
              |            |
              |            |
      -----------------------------
      |                           |
      |             ECM           |
      |                           |
      -----------------------------

The adapter board plugs into the ECM where the stock chip normally would be. The Ultimate's PROM connects through the adapter board to the PROM-related pins of the ECM connector. The ESC half of the stock MEMCAL connects through the adapter board to the ESC-related pins of the ECM connector. The PROM half of the stock MEMCAL is not connected to anything.

You can find out more about ECMs, MEMCALs, and chipping at the Chitown SyTy Tech page, Brian Green's chip stuff, HuRyde's Chippping section, and the old SyTy.org's PROM Guide.

Bill "InvisiBill" Talcott
invisibill@invisibill.net
Syclone 1456
September 15, 2003