Most modern petrol driven production cars are fitted with catalytic converters and an engine management system which electronically controls the air/fuel ratio (AFR), incorporating the use of an oxygen sensor and operating in what is known as a"closed loop" mode. Oxygen readings are transmitted to an engine management computer (ECU) along with various other parameters, and adjustments are electronically made to provide repeated self-correction of the AFR. This is intended to cause the engine to run at perfect combustion with an AFR of 14.75: 1 (also known as Factor 1).

This closed loop mode of operation can, however, render many faults difficult to diagnose. For example, a vehicle with an inlet manifold air leak would idle very erratically as the ECU attempts to compensate by adjusting the amount of fuel fed to the engine, based on incorrect readings taken from an air flow meter which is situated before the point of the air leak. This makes traditional diagnostic methods difficult as, in most case, it is necessary to make the engine stable before commencing common test procedures.

One approach to achieve stabilised running before curing a fault such as this is to take the vehicle out of closed loop mode and force it to run in an open loop condition by introducing a means for controlling the pulsing of the fuel injectors at a stabilised (non- f luctuating) rate. To achieve this by means of some kind of fuel controlling device and then to introduce a method of varying the pulses, the amount of fuel injected into the engine can be manually controlled. With the aid of an exhaust gas analyser many more tests can be performed such as catalytic converter testing when an engine is not running at Factor 1, by forcing it to do so and then monitoring the emissions from the exhaust.

According to the present invention a diagnostic/control device for fuel injected internal combustion engines comprises a control system having means for electrical connection directly to at least one fuel injector of an engine and to an engine management computer, and further means to actuate said at least one injector independently of the engine management computer.

Further according to the present invention there is provided a method of testing fuel injected internal combustion engines comprising the steps of providing a control system, electrically connecting the control system directly to at least one fuel injector of an engine in place of an engine management computer normally connected thereto, connecting the control system also to the engine management computer, and causing the control system to actuate said at least one injector independently of the engine management computer.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 illustrates a conventional closed loop computer controlled fuel injection system; Fig. 2 similarly illustrates a fuel injection system capable of operation in an open loop mode and including a control system connected in accordance with the invention.

Referring to Fig. 1 the fuel injectors of a four-cylinder internal combustion engine are illustrated at 10. Control, or pulsing, of the injectors is provided by an ECU 11 fed from the vehicle battery 12 and operating according to signals received from an oxygen sensor 13 which typically would be located in the exhaust system as close as possible to the engine and before any catalytic converter.

The ECU 11 is connected to the injectors 10 by leads 9 and to the oxygen sensor by a lead 8.

Referring now to Fig. 2, a control system provided in accordance with the invention is generally indicated at 14 and has been introduced"between"the ECU 11 and the injectors 10. Thus, the normal injector connection plugs 15 have been disconnected from the injectors 10 and have been replaced by four further leads 16 electrically connected to the control system 14. The oxygen sensor 13 is also connected at 17 to the control system. It will also be seen that one of the disconnected injector plugs 15a is connected at 18 to the control system 14 whereby the latter is connected also to the ECU 11.

As a result of these connections the control system 14 is directly and operably connected to the fuel injectors 10 and can control their operation independently of the ECU 11. However, the ECU must be connected to the control system to provide a reference signal for programme timings.

When the engine is started it will, by default, run in a "straight through"mode allowing the ECU 11 to have full control maintaining closed loop operation. However, it is possible now to store an injector pulse reading from the ECU 11 and continuously to reproduce it and manually modify it giving full control of fuel adjustment in an open loop mode of operation.

In this mode, the operation of the oxygen sensor 13 may be checked by the provision of two of the indicator lights on the control system showing the sensor's response to rich or lean running conditions.

From this mode it is possible to initiate an automatic mode of operation whereby the control system will continuously adjust the amount of fuel injected into the engine in response to the readings taken from the oxygen sensor much in the same way as does normally the ECU 11. However, unlike the ECU the control system 14 does not have connection to an array of sensors which give conflicting information during fault conditions.

The principal units within the control system 14, in addition to control buttons 3 and indicator lights 4 on a console 30, are a microprocessor 31, injector drivers 32, a voltage regulation suppression and protection device 33, an ECU injector input interface 34 and an oxygen sensor interface 35. The control system 14 cannot feed any signals back to the ECU therefore eliminating the possibility of damage thereto.

A number of diagnostic tests can be carried out with the system in view of the open loop mode in which it is capable of operation. For example, the catalytic converter may be tested by controlling the fuel supply to the injectors such that the correct AFR can be achieved and maintained, and thus the carbon monoxide or other emission content from the catalytic convertor may be checked using a gas analyser.

The oxygen sensor 13 itself may be checked as indicated previously by deliberately driving the engine rich and lean and checking whether the correct signals are received from the sensor.

Furthermore, if the system is used to ensure that the engine is running at Factor 1 i. e. an AFR of 14.75: 1 and the engine is capable of achieving this independently of the ECU, this may confirm that the ECU is faulty if other possible faults have been eliminated.

Inlet manifold air leaks may be detected where resultant low vacuum leads to under fuelling and rough running of the engine. The control system may be used to increase the injector opening time to determine whether the engine will then run correctly thus helping to diagnose that an air leak is present. Similarly, the fuel fed to an individual cylinder may be increased to help diagnose an air leak while leaving the ECU 11 to control the remaining cylinders.

The control system may be used to operate the injectors in a pulsed mode when they are placed in a cleaning bath.

Preferably, the system will be supplied with adaptors enabling it to be used on engines having more than four cylinders.

The system is simple to operate given a set of instruction for an operator to carry out various tests, the results of such tests being readily available and/or computable from test results.

The device may be extremely compact and sufficiently light weight to be hand-held with wiring looms of sufficient length that an operator may sit in the driving seat of the vehicle to conduct the tests.

In an alternative embodiment, a system in accordance with the invention may be permanently installed in a vehicle and, with signals received from appropriate sensors, can determine automatically when to take control of the injectors and when to return such control to the ECU. Thus, for example, the device may control the fuel injection according to predetermined parameters such as when the engine is at cruise with fuel conditions stabilised and the vehicle at a steady speed. Such operation is controlled entirely by the microprocessor with no need for control switches or indicator lights. Thus the device would not operate diagnostically but as a device to control and optimise fuel economy and exhaust emissions.

The cable harnesses can be connected directly into the vehicle wiring, and the oxygen sensor will be fitted to the exhaust.

Thus such an installation can be used effectively to upgrade older fuel injected vehicles to a closed loop system for exhaust gas monitoring to achieve more economical running with lesser hazardous emissions.