BMW Coupes and Sedans 1970-1988 Repair Guide

BOSCH L-JETRONIC AND MOTRONIC FUEL INJECTION SYSTEMS

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See Figures 1, 2, 3 and 4

The Bosch L-Jetronic fuel injection system is electronically controlled to regulate the fuel supply in relation to the air flow. An air flow meter, located in the air intake chamber, converts angular movement of an air baffle plate into a voltage signal, which is sent to the control unit.

As the engine begins its revolution, twin contacts, located 180° apart in the base of the distributor, trigger current impulses to the control unit at one impulse per crankshaft rotation.



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Fig. Fig. 1: Schematic of Bosch® L-Jetronic system



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Fig. Fig. 2: Schematic of Bosch® Motronic system



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Fig. Fig. 3: Model 630i fuel flow diagram



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Fig. Fig. 4: Model 633CSi fuel flow diagram

After computation of the signals, a command signal is sent from the control unit to the electromagnetic injector valve, which are wired in a parallel circuit, causing them to open simultaneously. To obtain smooth combustion, half the total fuel volume necessary for the engine cycle, is injected per half rotation of the camshaft, which corresponds to each rotation of the crankshaft.

Automatic cold start and warm-up devices are incorporated in the system to give better driveability and engine operation during the initial start and warm-up period, when added fuel is needed.

 
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