4-cylinder engines (Mono-Motronic)
From the Mono-Motronic fuel mixture preparation unit, the mixture of air and fuel enters the cylinders through the intake manifold. If the intake manifold is cold, then a significant part of the mixture condenses on the inner walls of the manifold and enters the combustion chambers, not quite in the form of vapors. This misfortune can be helped by double heating the intake manifold.
On a cold engine, the electrically heated intake manifold is activated. It consists of an electrically heated «hedgehog», which is screwed into the intake manifold below the fuel mixture preparation unit. Our «hedgehog» with a natural animal, only needles are common. In the Audi-100, they serve to increase the surface of the heating element «hedgehog» the heating is only effective up to a coolant temperature of 65°C. Then the current is turned off.
Thermal switch (shown on electrical diagrams as «coolant temperature sensor - G62») includes «hedgehog» not directly. G62 supplies the Mono-Motronic control unit with information about the temperature, and this latter, through a relay in an additional relay box under the dashboard, gives the order to apply power to «hedgehog».
At higher temperatures, the heating of the intake manifold is taken over by the coolant. To do this, an additional amount of the total coolant flow is directed through a special channel in the intake manifold.
On the left: the temperature controller for the intake air heating is located in the air intake housing of the 74 kW engine; from the outside it is easy to recognize the thermostat by the hose connections to the hot air damper (1) and to the combustible mixture preparation unit (2).
Right: for heating the air-fuel mixture into the air intake sleeve of a 74 kW engine (with Mono-Motronic injection system) mounted «hedgehog» (1). Position 2 shows the connecting wire.
Left: The variable intake manifold flaps of the 2.8-litre 6-cylinder engine are actuated by means of a membrane mechanism marked with an arrow.
Right: this «valve for switching the sequential intake manifold» (2) determines whether rarefied air can enter the membrane mechanism. The valve is located on the right rear in the engine compartment under the air flow meter (1).
Intake manifold heating test
Examination «hedgehog»: With a cold engine, disconnect the wire leading to «hedgehog» under the intake manifold, at the plug connection (it is installed on the side of the combustible mixture preparation unit).
on the cable to «hedgehog» and to «mass» connect an ohmmeter: if it shows 0.25-0.50 ohms, then it means «hedgehog» in order.
Whoever does not have an ohmmeter should remove the fuel mixture preparation unit with a cold engine, turn on the ignition and check with a wet finger if the needles are heating up «hedgehog».
If «hedgehog» does not heat up, despite the correct resistance indicators, then the reason may be in a defective relay.
Checking the thermal switch: (see chapter «Mono-Motronic injection system»).
Relay check. (Chapter «Body electrical system»).
Visitor comments