Volvo Engine Repair Instructions

Volvo Engine Repair Instructions

Magnetically controlled proportional valve (MPROP)

A magnetically controlled proportional valve (MPROP) controls the high pressure pump to ensure that the correct fuel pressure (rail pressure) is retained despite varying engine speed and loading.

The input signal to the valve is a PWM signal whose pulse width is controlled by the engine control module. When the current through the valve is changed, this affects the fuel flow, which results in changed rail pressure.

Water in fuel switch, secondary fuel filter

A switch is located in the water trap under the fuel filter. Its task is to detect whether there is water in the fuel. The switch senses the resistance between two pins, wich are in contact with the fuel. When there is no water in the fuel, the resistance is very high. If there is any water in the fuel, the resistance falls.

Switch, coolant level

The task of the switch is to discover whether the coolant level in the engine (expansion tank) has become too low. An alarm signal is sent when the coolant level is too low.

Preheater with preheater relay

The preheater is located in the inlet manifold at the left side of the engine. The preheat relay is located at the engines left side beneath the preheater.

Engine control unit, EMS 2

The engine control unit checks and controls the injectors, to ensure that the correct volume of fuel is injected into each cylinder at the right time. It also controls the high pressure pump via the proportional valve (MPROP) to ensure that the system always has the correct fuel pressure (rail pressure).

The control unit also calculates and adjusts the injection advance. Regulation is mainly done with the aid of the engine speed sensor and the combined sensor for air inlet pressure/inlet manifold temperature.

The EMS 2 system processor is located in the control unit, protected from water and vibration.

The processor receives continuous information about:

• Engine Speed

• Throttle

• Oil Pressure

• Air inlet pressure/temperature

• Fuel pressure (common rail pressure)

• Fuel alarm, “Water in Fuel”

• Camshaft position

• Coolant temperature

The information provides information about current operation conditions and allows the processor to calculate the correct fuel volume, monitor engine status etc.

Repair Instructions

General advice on working with EMS engines

The following advice must be followed to avoid damage to the engine control unit and other electronics.

IMPORTANT!

The system must be disconnected from system voltage (by cutting the current with the main switch) and the starter key(s) must be in the 0 position when the engine control unit connectors are disconnected or connected.

• Never disconnect the current with the main switches when an engine is running.

• Never undo a battery cable when the engine is running.

• Turn the main switches off or disconnect the battery cables during quick charging of the batteries.

NOTICE! During normal trickle charging, it is not necessary to turn the main switches off.

• Only batteries may be used for start help. A help start device can produce a very high voltage and damage the control unit and other electronics.

• If a connector is disconnected from a sensor, be very careful to avoid allowing the contact pins to come into contact with oil, water or dirt.

IMPORTANT!

The system must be disconnected from system voltage when the engine control unit connectors are disconnected or connected.

2 Undo the two connectors from the engine control unit before any electrical welding starts. Turn the locking arm down at the same time as the connector is pulled outwards.

3 Disconnect all connections to the alternator. Connect the welder earth clamp to the component

to be welded, or as close as possible to the weld site. The clamp must never be connected to the

engine or in such a way that current can pass through a bearing.

IMPORTANT!

After welding is completed, the disconnected components, such as alternator cables and battery

cables must be connected in the correct order. The battery cables must always be connected last.

Changing the engine control unit

1 NOTICE! Cut the current with the main switch.

IMPORTANT!

The system must be disconnected from system voltage when the engine control module connectors are disconnected or connected*.

2 Remove the two connectors from the engine control unit. Turn the locking arm down at the same time as the connector is pulled outwards

3 If the new engine control unit has recently been programmed:

Start the engine and check whether any fault codes related to the engine control unit occur.

Checking the starter motor voltage

Tools:

88890074 Multimeter

General

If battery voltage falls below 24.7 V*, the starter motor will not be able to crank the engine at normal speed. A fully charged battery has an open circuit voltage of about 12.7 V.

NOTICE! * Measured on the batteries. Voltage measurement, check

1 Check that the battery voltage is at least 24.7 V when unloaded by using 88890074 Multimeter to measure between the battery poles.

2 Turn the main switch on.

3 Check that the voltage between terminal B+ on the starter motor and battery negatives connection point is the same as the battery voltage.

Checking the charging system

Generally about alternators:

The voltage output from an alternator must be limited to prevent the elecrolyte in the battery to evaporate. The alternator output is regulated (limited) by the voltage regulator in the alternator. The maximum current that the alternator can deliver at regulated voltage output depends on the alternator revolution. When the Volvo diesel engine is started an excitation current is needed to “wake up” the alternator.

NOTICE! It is the consumers (batteries included) which decides the output current from the alternator.