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F or years the experts have been telling us that the

2nd April 1992, Page 96
2nd April 1992
Page 96
Page 97
Page 96, 2nd April 1992 — F or years the experts have been telling us that the
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future of vehicle maintenance lies in diagnostics. Workshop has looked at three approaches to diagnostics: bespoke; intervention; and nonintervention systems.

For an example of a bespoke system we picked Iveco Ford's Modus, which is designed to operate on the company's own range of vehicles.

Souriau's Optima 4080 requires several sensor tappings to be put on to an engine, but it can work with any diesel engine. VL Churchill is marketing the AVL 845 which does not need any special connectors on the engine.

Modus (Turbo 70) is an "expert" computerised diagnostic system. So far it has been programmed with all the relevant data for the New Cargo and the relevant fault finding sequences. The example we saw in action was a prototype as the system is still under development.

The engine testing module is separate from the main computer and connects to a socket in the dashboard. New Cargo has two sensors detecting the flywheel, and one on the camshaft: all are fitted on-line. Others check the exhaust for the diesel temperature; Modus has its own atmospheric pressure sensor.

The engine type, power rating and the clutch type must be fed into the system before testing begins. Normally the first thing to be checked is torque. This entails starting the engine and revving to its governed speed. The system reads instantaneous acceleration of the flywheel using the two sensors and displays the results cylinder by cylinder. It knows what torque the engine should produce and will interpret the results as "good", "passable" or "bad".

The compression Lest is made by accelerating the engine to full speed, shutting off the fuel supply and seeing how long it takes the engine to stop. Again, it reads out cylinder by cylinder.

If there is a problem a microphone is clamped to the oil filler opening while the Souriau's system requires tappings on the fuel, air and exhaust systems. Churchill's system is an example of diagnostics which are attached temporarily when required.

Instrumentation of an engine for Souriau's 4080 (Turbo 71) should, with a little practice, take around 2.5 hours, using fittings that cost between f-80 and £130.

Connectors

Connectors have to be plumbed in to the system to allow oil pressure, exhaust temperature, fuel pressure before and after the filter and air pressure (or vacuum) before and after the filter to be measured. Pressure readings are also taken on the inlet and exhaust sides of the turbocharger.

These connectors are left permanently on the engine and the corresponding pipes or sensors are inserted at each test.

Also connected for each test is a clamp on number one injector pipe; temperature sensors clamped on the oil and coolant hoses; a TDC sensor that counts the teeth on the flywheel; and electrical connections

form by the computer, which will sort them into nine sections: air cleaner pressure drop; turbo boost pressure; exhaust back pressure; lift pump pressure; fuel filter pressure drop; lubrication oil pressure; oil temperature; engine coolant temperature; and exhaust temperature.

Each section is given a result of "good" or "bad". Some parameters are programmed into the system, but its real advantage is an ability to compare results with previous tests on the same vehicle.

Bad results are highlighted on the screen and the "expert" system will guide the technician through the fault finding process by a series of yes/no questions.

In the case of, say, lift pump pressure, the system would ask: "Is there a sedimentor which is blocked?" "Is the pipe between the tank and the pump blocked?" "Are there any leaks?" "Is the tank venting?"

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Organisations: US Federal Reserve
People: Churchill

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