VOLVO Repair Manual - Table of Content [200] [700] [900]
by www.VLVworld.com - Your Internet VOLVO Part and Accessory Store Since 1997 - All rights reserved
2.5 Fuel Injection
2.5.1 Air Filter
2.5.2 Air Mass Meter
2.5.3 Oxygen Sensor/Lambda Sond
2.5.4 Engine Coolant Temperature Sensor/Thermal Switch
2.5.5 Main Fuel Pump and Fuel Filter
2.5.6 In-Tank Fuel Pump
2.5.7 Throttle Switch
2.5.8 Pressure Regulator
2.5.9 ECU- Electronic Control Unit

Introduction

This section describes how to change or check the above parts. The fuel injection system can be complicated to troubleshoot, but hopefully this guide will aid in your understanding of how each component functions. You can find and purchase most of the parts described here in the following parts catalogue pages from VLVworld.com:

240/260 Fuel Injection catalogue page

740/760/780 Fuel Injection catalogue page

940/960/S90/V90 Fuel Injection catalogue page

Troubleshooting
Difficulty Starting Blown Fuse
Faulty Air Mass Meter
Ring Gear (flywheel) Damage
Typical LH Jet Fuel Injection System (found on 1983-1995 engines) LH 2.4 Shown
Move your mouse over each component in the diagram to see a photograph.
A Battery
B Ignition Switch
C System Relay
D AC Control
E AC Compressor
F System Displays
G Fuel System Control Unit (ECU)
H Ignition System Control Unit
I Diagnostic Unit
J Idle Valve
K Throttle Switch
L Air mass meter
M Carbon Filter/EVAP valve
N Roll-over valve
O In-tank Fuel Pump
P Main Fuel Pump/ Fuel Filter
Q Oxygen Sensor
R Coolant Temperature Sensor
S Cold Start Valve
T Injectors
U Pressure Regulator
V Fuel Distribution Pipe


2.5.1 Air filter

The air filter ensures that only clean air enters the engine. When the air filter is dirty it can restrict the air flow passing through it. Air filters should be replaced every 30,000mi (50,000km) or when dirty.

Replacement Procedure
  • Locate the airbox (usually in the front corner opposite the battery)
  • Remove any air hoses attached to the lid of the airbox
  • Release the lid clips and remove the lid
  • Remove the air filter from the housing
  • Install the new filter, ensuring that the rubber seal sits in the groove
  • Realign the lid and fasten the clips
  • Reinstall any air hoses previously removed from the airbox lid



2.5.2 Air Mass Meter

The air mass meter, or air flow meter, measures the mass of the air flowing in the intake air duct. The AMM then sends a signal to the ECU which adjusts the air/fuel ratio accordingly. Inside the AMM is a fragile, thin filament which may become damaged and necessitate replacement of the unit. A faulty AMM can cause no start faults or 'stall' the car when it's running. If the car is experiencing such problems but runs adequately with the amm disconnected, then the amm should be replaced. Driving with the air mass meter disconnected is often referred to as "limp-home" mode and is not a long term solution.

Replacement Procedure
  • Push downwards on the metal clip of the electrical connector at the top of the air mass meter and disconnect
  • Undo the two clips from the airbox
  • Undo loosen the worm gear on the hose clamp
  • Slide the air mass meter out from the airbox and the air hose
  • Check that the serial number is identical on both the old the and replacement air mass meter
Part Numbers
VOLVO air mass meters have the part number written on them. It is important to replace with the same model. The last three digits are the key to identifying the amm.


2.5.3 Oxygen Sensor/Lambda Sond

The oxygen sensor measures the oxygen content of the exhaust gas. It is positioned in the exhaust manifold. VOLVOs use a three wire oxygen sensor: two wires providing a current to heat the sensor, and the remaining wire for the output signal. The voltage of the output signal should oscillate between 0.1 and 0.9 volts. Replacing a faulty sensor will increase the fuel efficiency and reduce emissions. It is recommended that they be replaced every 30,000 miles (50,000 km).
Some volvos have a 'Lambda Sond' light that illuminates at certain mileage intervals as a reminder to change the oxygen sensor. This periodic warning light is separate from the sensor and can be reset via a button on the unit.


Figure 2.5.3a Oxygen Sensor (viewed from underneath)

2.5.4 Engine Temperature Sensor (Thermal Switch)

The function of the engine temperature sensor is to notify the ecu of the engine temperature, so it can manage the air/fuel ratio. The sensor is submerged in the coolant and changes resistance depending on the temperature (more resistance at lower temperatures). If there is a wiring fault the resistance may seem extremely high and the ecu would assume that the engine is extremely cold.
A cold engine requires a more fuel heavy air/fuel ratio than a hot engine. A faulty sensor registering an extremely cold engine would result in too much fuel being sent into the cylinders and the engine would run rich. Symptoms of this include: high idle, flooded engine, poor running (especially when warm), difficulty starting, stalling, and gas in oil.

Accessing the Temperature Sensor
  • Access to the temperature sensor is limited at best. It was necessary to remove the intake manifold just to get an acceptable picture of the temperature sensor. Since the sensor is not often removed it may be stiff to undo and the additional space is beneficial.
  • You may try undoing the temperature sensor with the intake manifold installed. First remove the plastic clip from the sensor, then use a 19mm socket or wrench to undo the sensor.
  • To remove the intake manifold:
    • Undo the 8 x 13mm securing nuts
    • Detach the manifold hoses
    • Unclip the injectors (note to which injector each attaches)
    • Undo the two 10mm grounding bolts
    • Undo the 12mm bolt from the lower support
    • Detach the throttle and cruise control cables
  • Once the intake manifold detach the wiring and use a 19mm socket or wrench to remove the sensor
  • While the manifold is out it is also a good time to clean the oil box (directly below), and inspect the knock sensor and temperature gauge sensor wiring.

Figure 2.5.4a Block Temperature Sensors and Knock Sensor


2.5.5 Main Fuel Pump / Fuel Filter

The fuel pumps deliver fuel from the rear mounted fuel tank, through the fuel filter, and into the injectors. VOLVOs are fitted with two fuel pumps: a main pump located under the car and an in-tank pump. A car will run with a faulty in-tank pump, but it places additional strain on the main pump. If the main pump is replaced it is also wise to change the fuel filter, which is located along side the pump. Problems with the main fuel pump are sometimes related to the fuel pump relay [200 Relay / 700 Relay] which provides power to both the pumps.

The fuel flows through the fuel filter directly after passing through the pump. A clogged filter can cause sluggish performance, hesitation and other fuel starvation problems. Fuel filter replacement

Testing the Fuel Pump

  • Safely jack up the car
  • Locate the fuel pump beneath the car (approximately under the drivers seat)
  • Disconnect the black and yellow electrical connectors
  • Connect a battery directly to the pump (black is negative, yellow is positive)
  • If the pump functions, then the problems is related to the power supply (fuel pump relay, wiring, computer)
  • A noisy main fuel pump can indicate failure of the in-tank pump(Section 2.5.6)
Replacement Procedure
  • Safely jack up the car
  • Undo the fuel pump electrical connectors
  • Detach the fuel hoses (have a catch pan ready)
  • Undo the mounting bracket from the car
  • Disconnect
Figure 2.5.5a Main Fuel Pump


Figure 2.5.5b Fuel Filter

2.5.6 In-tank Fuel Pump

The in-tank fuel pump is mounted with the fuel gauge sending unit inside the tank. This unit is accessed by a panel inside the trunk. If the fuel gauge is not working it is usually caused by wiring faults above the unit. Fuel smells towards the rear of the car are often caused by corroded fuel pipes near the in-tank pump.
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In-tank Fuel Pump Removal
  • Ensure that the tank is less than half full
  • Disconnect the negative cable from the battery
  • Sedan- remove the spare tire panel, spare tire, and fold back the carpet from the rear left of the trunk
    Wagon- fold down the rear seats, pull back on the hinged cover, and remove the securing screws
  • Undo the hatch corner screws and remove the access hatch
  • On the lid directly under the access hatch you should find pump/fuel gauge wiring and fuel supply hoses
  • On the wiring locate the connector (about 20 cm from the tank) and undo. DO NOT pull on the wiring where it passes through the lid, this is a fragile point and is difficult to repair
  • Undo the ground wire bolt
  • Disconnect the hoses attached to the lid
  • Undo the lid- it is attached by either 6 nuts on studs (until ~86) or a large plastic nut (later models). Access can be difficult to some of the nuts.
  • Lift up on the unit and twist to ease removal. Do not force the unit; gently pull and turn until it is free.
  • Determine the cause of the fault and repair. The fuel gauge sender should register increasing resistance as it empties (from 36 ohms-full tank to 296 ohms-empty tank)
  • Reinstall the unit

Figure 2.5.6a In-tank Fuel Pump

2.5.7 Throttle Switch

The throttle body is mounted on the intake manifold. Inside the unit there is a flap that opens as the accelerator is pressed. On the edge of the unit there is a throttle switch that senses the position of the throttle body. This information is then sent on to the ecu.

Symptoms of a bad throttle switch are high or uncontrolled idle at startup (above 750rpm).

Throttle Switch Testing(When high or uncontrolled idle is the problem)

  • Unclip the electrical connector
  • Connect one of the outer pins to the center one
  • If idle returns to normal then the switch is at fault (try adjusting before replacing)
Throttle Body Removal

  • Undo the large air intake pipe
  • Unclip the throttle switch connector
  • Undo the securing bolts and any other hoses
  • Remove, tap lightly if stuck
  • When the unit is removed, open the flap and wipe the inside to clean. Also check that none of the pipes are clogged. Switch adjustment should also be performed with the throttle body removed
  • Install a new gasket if needed when reinstalling

Throttle Switch Adjustment
  • Remove the throttle body from the car and clean- ensure the interior flap closes properly
  • Test the current switch position:
    • Close the flap with a .15mm feeler gauge inserted behind the stop screw, a 'click' should be heard
    • Close the flap with a .45mm feeler gauge inserted behind the stop screw, no 'click' should be heard
  • If the switch need adjusting, loosen the switch adjustment screws
  • Hold the interior flap closed and rotate the switch clockwise until it stops and then counter clockwise until it engages the flap
  • Tighten the adjustment screws
  • Test the switch again and adjust if necessary

Figure 2.5.7a Throttle Switch mounted on a Throttle Body


Figure 2.5.7b Throttle Switch Location

2.5.8 Fuel Pressure Regulator (FPR)

The fuel pressure regulator is located at the end of the fuel distribution pipe. It's function is to regulate the fuel pressure at the injectors relative to the throttle opening.

A faulty FPR can cause a variety of problems (possibly intermittent): stalling, no start, poor acceleration, running rich (using too much fuel), etc. The pressure regulator is known to fail, especially on older, higher mileage cars. Inside the regulator is a diaphragm. If this breaks then fuel can leak back into the intake manifold.

Testing

  • Undo the vacuum line (the black tube in Fig 2.5.8a) and smell for fuel at the hole. Fuel at the vacuum hole indicates that the diaphragm is broken at the pressure regulator needs to be replaced.
  • Disconnect the return line from the regulator- directly opposite the vacuum line.
  • Connect some pipe in place of the return line
  • Direct the end of the pipe into a gasoline safe container
  • Run the car at idle
  • A good, solid stream of fuel should flow into the container
Replacement
  • Disconnect the vacuum line
  • Unclip the connector to the fuel distribution pipe (sometimes a nut, which must be undone)
  • Remove the mounting bolt
  • Remove the regulator and replace

Figure 2.5.8a Fuel Pressure Regulator

2.5.9 Electronic Control Unit (ECU)/ Fuel System Control Unit

The electronic control unit, or ecu, governs the engine management and monitors many of the electronic sensors. All volvos with fuel injection are dependent on their ecu to run.

The ECU does not ordinarily fail, however the housing can become corroded due to its location in the passenger foot well. The carpet in that region can become soaked with salt and moisture and have the effects as shown in Figure 2.5.9b. (The ecu in the picture was taken from a running vehicle). In a situation of a corroded housing it is recommended to cut back the carpet from underneath the ecu and cover the exposed corner with card and tape.

Replacement Procedure
  • Unclip the plastic screw cover from the front passenger side door sill
  • Unscrew the philips head screw and slide the side panel towards the rear of the car to remove
  • Unclip the ecu wiring
  • Undo the two philips head screws on the ecu mounting frame
  • Slide the ecu unit towards the rear of the car to remove it from the frame

Figure 2.5.9a Electronic Control Unit


Figure 2.5.9b Corroded Electronic Control Unit

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