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This article written by Peter Kay describes in detail the operation and ECU details of the Bosch Motronic fuel injection system.
Excerpt from the attachment:
Fault Diagnosis On Motronic M1.5 Engine Management System
Introduction
From Model Year 1990, when catalytic converters were first fitted to the range, all Senator and Carlton GSi models incorporated the Bosch Motronic M1.5 engine management system. The engines in these models were coded as either C30NE; (The 3.0 Litre 12V engine.) C30SE; (The 3.0 Litre 24Valve engine.) or C26NE (The 2.6 Litre engine.), the ‘C’ indicating the fitment of ‘Cats.’. From experience, the system is very reliable and problems encountered are usually caused by poor contact at the associated plug/socket combinations that link the various system sensors to the Electronic Control Unit (ECU). The electrical diagrams for these vehicles, issued by the manufacturers and others, are poorly presented and can easily cause confusion when attempting to trace a particular element of the engine management system. In consequence, fault finding on the engine electrics can be somewhat frustrating.
To improve this situation, Figure 1 on the following page, shows the complete engine management system in detail and includes all connectors and associated wiring, including all direct connections to the ECU.
Since the primary purpose of this article is to assist in the location of faults in the Engine Management System, the diagram as been kept as clear as possible, therefore, connections to other peripheral systems e.g. Cruise Control, Ride Height etc. are not shown.
This particularly applies to outputs from the Distance Sensor (P14) which, from
Pin 2, supplies an output to many of these associated circuits. However, if the Mileometer is operating correctly, it can be safely assumed that P14 is also giving the correct output signal.
When a possible fault has been deduced by reference to Figure 1, then it can be confirmed by checking for satisfactory signal levels at the relevant pins of the ECU
Table 1, lists each pin of the ECU, in numerical order, and the expected ‘Satisfactory Readings’ under specified ‘Engine/Ignition’ conditions, when measured with respect to an associated ‘Ground Reference Pin’.
Details on how to access the ‘Related Blink Codes’, that are given in the last column of Table 1, is the concluding part of this article.
Measurement of Signal Level On ECU Pins.
To gain access to the ECU, remove the plastic cover panel, located in the drivers foot well, at the outer side of the vehicle. Access to the relevant pins of the ECU for measurement is then achieved by releasing the screws securing the rear cover of the connecting plug then carefully removing it to expose the rear of the pins.
The following illustration shows the pin layout of this connector.
All measurements must be made using a digital multimeter or portable oscilloscope, as appropriate, pressing the instrument probes between the pin to be measured and the ‘Associated Reference Pin’, given along side it, in Table 1. CAUTION: Do not use a simple analogue multimeter as, in some circumstances, it would ‘load’ the ECU circuit under test, giving a false reading.