There are four basic ECUs (DMEs) used on normally aspirated 911 Porsche 3.6 engines from 1989 (964-C4) through 1998 (993). The Turbo control units are different and not discussed here.


DriveBlok is a technology that Porsche began using in 1994/1995 which disables the DME/ECU unless it gets a unique signal from the vehicle’s security and alarm system.  It can only be disabled by reprogramming or replacing the ECU. It was present in all US ECUs starting in 1996.

  1. 1989-1994 964 – these are essentially the same. They have a 55 pin connector and are designed for the Bosch “Barn Door” style airflow meter, in use since the 1983 944 and 1984 3.2 Carreras.  These have dual circuit boards and are difficult to open since the upper row of pins on the connector goes into the upper circuit board.  These have ignition circuits that use a pair of single-channel igniters which are bolted to the dual-coil pack.
  2. 1994-1995 993 and 1996-1998 Euro Varioram.  These are identical other than programming.  They have a 55-pin connector and a replaceable 512K EPROM chip.  The chip determines functionality from emissions controls to actuation of the resonator flap and VariRAM function if so attached.  These have a single circuit board and use a single igniter.  The chips come in four basic varieties, though many other combinations can be programmed or used on RS/Supercup/etc. models.
    1. DriveBlok vs No DriveBlok:  If the 3rd set of numbers on the ECU have a 124, the unit is Drivebloked and needs to talk to the alarm system to function.  That can be remedied by replacing the chip.  Example of Unlocked is 993.618.123.XX, DriveBlock is 993.618.124.XX
    2. Secondary Air System: US vs Euro: The US versions (95 only) operate the secondary air system which blows air into the exhaust port.  The Euro version does not have this functionality, though it can be enabled by swapping the chip.
    3. 95 vs VRam (96-98) Euro: The European Varioram version of the DME enables a channel to operate the Varioram. This can be enabled through a chip swap.  Note that the Secondary Air system and the Varioram operation are mutually exclusive, the DME cannot operate both.
  3. 1996 US Varioram: This is a one-year ECU and is OBD-II compliant.  The chip that determines functionality is soldered to the main circuit board and is DriveBloked.  This ECU has 88 pins and looks completely different from the 1989-1995 ECUs and has integral igniters (ignition coil drivers). While several firms over the years have claimed to be able to solder a new socket into the circuit board and insert a programmable chip, every one of these I have seen has eventually failed, and no warranty was given.  Since there is no easy way to remove the DrivBlock, these cannot be used in conversions.  While I have heard of people installing the main wiring harness, infrared receiver, alarm system, etc. to get these to work, I don’t think it’s worth the additional effort.  Part Numbers are 993.618.601.xx or 993.618.604.xx.  You may need to check the date code, 96 is generally though 6/96.
  4. 1997-98 US Varioram: THese are similar to the 1996 US Varioram units but have a reprogrammable chip.  Plan on spending about $1000 to have these “re-flashed” to remove DriveBlok.  Reprogramming for a performance tune is available though not nearly as widely or inexpensively as the 55-pin boxes. Part Numbers are 993.618.604.xx

Options for Varioram:  If you have a Varioram engine or are installing the Varioram intake we recommend converting to the 1995 or Euro993 harness and ECU.  We can modify the 1996-1998 harness by replacing the connector.  We also build fresh harnesses out of MIL-Spec PTFE silver plated wire.

You will also need to replace the ECU.  This is the best option when dealing with 1996 engines and gives a lot more flexibility as we (or others, like Steve Wong, 911 Chips) can tune it easily.