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LH 2.4 Overview



Overview, LH-Jetronic:

(From Wikipedia)
''Digital fuel injection, introduced for California bound 1982 Volvo 240 models. The 'LH' stands for German: "Luftmasse-Hitzdraht" - the hotwire anemometer technology used to determine the mass of air into the engine. This air mass meter is called HLM2 (Hitzdraht-LuftMassenmesser 2) by Bosch.

The LH-Jetronic was mostly used by Scandinavian car manufacturers, and by sports and luxury cars produced in small quantities, such as Porsche 928. The most common variants are LH 2.2, which uses an Intel 8049 (MCS-48) microcontroller, and usually a 4 kB programme memory, and LH 2.4, which uses a Siemens 80535 microcontroller (a variant of Intel's 8051/MCS-51 architecture) and 32 kB programme memory based on the 27C256 chip.

LH-Jetronic 2.4 has adaptive lambda control, and support for a variety of advanced features; incincluding fuel enrichment based on exhaust gas temperature (ex. Volvo B204GT/B204FT engines). Some later (post-1995) versions contain hardware support for first generation diagnostics according to ISO 9141 (a.k.a. OBD-II) and immobiliser functions. The 1995 and newer Volvo 940 vehicles are one such example.''


Fuel Injection Computer

  • Internal Hardware
    * CPU: Siemens 80535 (Intel 8051/8052 variant), Incorrect parameter fileId, Incorrect parameter fileId
    * RAM: Internal 256 bytes with battery backed section, optional external
    * ROM: External, 27C256 (32k)
  • Inputs
    * Coolant Temperature
    * Air Mass Sensor: Incorrect parameter fileId
    * RPM (from EZK)
    * Knock (from EZK)
    * Throttle switch (closed, open, and WOT)
    * Lambda probe (Narrowband O2 Sensor)
    * Vehicle speed (from dashboard/speedometer)
  • Outputs
    * Single injector channel (batch fire)
    * Idle air control valve
    * Electronic fan control (low and high speed)
    * Canister purge valve
    * Fuel pump/main relay
    * Tq/Load signal (to EZK)
    * Diagnostic connector (K-line, linked to internal UART)



Ignition Computer (EZK)

  • Internal Hardware
    * CPU: Siemens 80535 (Intel 8051/8052 variant), Incorrect parameter fileId, Incorrect parameter fileId
    * RAM: Internal 256 bytes, no external or battery-backed RAM
    * ROM: Internal CPU OTP ROM, or External 27C256 (see datasheet)
  • Inputs
    * Engine speed sensor (VR sensor, 60-2 on flywheel)
    * Knock sensor (piezoelectric)
    * Coolant temperature (shared sensor w/fuel computer)
    * EGR Temperature (optional)
    * Throttle position switch
    * Tq/Load signal from fuel computer
  • Outputs
    * Single ignition output to external power stage
    * EGR control output (optional)
    * Diagonstic connector output

Wiring Diagram (generic)




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