Ford Sierra Manual

General information and precautions
Fuel and exhaust systems - carburettor / General information and precautions


General information
The fuel system on carburettor models may comprise a fuel tank, a fuel pump, a fuel pressure regulator and/or vapour separator, a downdraught carburettor and a thermostatically-controlled air cleaner.

On Saloon, Hatchback and Estate models, the fuel tank is mounted under the rear of the vehicle, on the right-hand side. On P100 models, the fuel tank is mounted behind the cab, between the chassis frame and the load area. The tank is ventilated, and has a simple filler pipe and a fuel gauge sender unit.

The mechanical fuel pump is a diaphragm type, actuated by a pushrod bearing on an eccentric cam on the auxiliary shaft on SOHC models, or on the camshaft on CVH models.

DOHC models and models with air conditioning have an electric fuel pump mounted under the rear of the vehicle, next to the fuel tank. DOHC models have a combined pump and fuel level sender unit.

The fuel pressure regulator and/or vapour separator is used to stabilise the fuel supply to the carburettor. The pressure regulator provides a constant fuel pressure, and hence maintains a constant float level in the carburettor which reduces exhaust emission levels. The vapour separator purges vapour from the carburettor fuel supply, thus improving hot starting qualities. All models up to 1985 are fitted with a fuel pressure regulator. All models from 1985 except 2.0 litre SOHC models and CVH models are fitted with a combined fuel pressure regulator/ vapour separator. 2.0 litre models from 1985 and CVH models are fitted with a vapour separator only. DOHC models have no pressure regulator or vapour separator fitted.

The carburettor may be either a Ford variable venturi (VV) type, a Weber twin venturi (2V or 2V TLD) type, or a Pierburg twin venturi (2V) type, depending on model. Each type of carburettor is available in several versions to suit particular engine and equipment combinations.

The air cleaner has a vacuum or waxstat controlled air inlet supplying a blend of hot and cold air to suit the prevailing engine operating conditions.

Precautions
Warning - Fuel - Many of the procedures given in this Chapter involve the
disconnection of fuel pipes and system components which may result in some fuel spillage. Before carrying out any operation on the fuel system, refer to the precautions given in the УSafety firstФ Section at the beginning of this manual and follow them implicitly. Petrol Is a highly dangerous and volatile substance, and the precautions necessary when handling it cannot be over stressed.

Tamperproof adjustment screws - caution
Certain adjustment points in the fuel system (and elsewhere) are protected by УtamperproofФ caps, plugs or seals. The purpose of such tamperproofing is to discourage, and to detent, adjustment by unqualified operators.

In some EEC countries (though not yet in the UK) it is an offence to drive a vehicle with missing or broken tamperproof seals. Before disturbing a tamperproof seal, satisfy yourself that you will not be breaking local or national anti-pollution regulations by doing so. Fit a new seal when adjustment is complete when this is required by law.

Do not break tamperproof seals on a vehicle which is still under warranty.

Work proceedures
When working on fuel system components, scrupulous cleanliness must be observed, and care must be taken not to introduce any foreign matter into fuel lines or components.

Carburettors in particular are delicate instruments, and care should be taken not to disturb any components unnecessarily.

Before attempting work on a carburettor, ensure that the relevant spares are available.

Full overhaul procedures for carburettors have not been given in this Chapter, as complete strip-down of a carburettor is unlikely to cure a fault which is not immediately obvious, without introducing new problems. If persistent problems are encountered, it is recommended that the advice of a Ford dealer or carburettor specialist is sought. Most dealers will be able to provide carburettor rejetting and servicing facilities, and if necessary it should be possible to purchase a reconditioned carburettor of the relevant type.


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