Volvo 240/740/760/780/940/960 1990-1998

General Information


See Figure 1

The Motronic 4.3 and 4.4 system on 850/C70/S70/V70 models is a total control system. Both engine and ignition controls are incorporated into one system with one control module. The control module receives the inputs from various sensors and controls all the outputs together.

The inputs that directly affect ignition include the RPM sensor (crankshaft position sensor), Camshaft Position (CMP) sensor, knock sensors, Engine Coolant Temperature (ECT) sensor, Mass Air Flow (MAF) sensor, acceleration sensor, Throttle Position (TP) sensor and, on vehicles equipped with an automatic transaxle, a Transmission Control Module (TCM). The RPM and CMP sensors determine engine speed and directly affect ignition timing control. The TP and MAF sensors, as well as the TCM, determine engine load. The knock sensor determines if the ignition timing is correct by detecting engine knocks or pre-ignition, and the acceleration sensor determines if the vehicle is being driven on a bumpy or uneven surface, possibly causing faulty knock sensor readings.

The system has a fail safe or limp home mode where it defaults to a predetermined timing and voltage level if an input device fails. The Malfunction Indicator Lamp (MIL) will illuminate and the vehicle may exhibit more driveability problems; it should be diagnosed as soon as possible.

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Fig. Fig. 1: Motronic 4.3 distributor ignition system