Dacia Pick-Up 1304/1305/1307. Manual - part 39

IGNITION AND  INJECTION

17

17 - 20

  OXYGEN SENSOR ( Lambda )

The oxygen sensor (Lambda) is fixed on the primary down tube, in front of the catalytic

converter. Its purpose is to determine the oxygen content of the exhausted gases; this
oxygen content value depends upon the dosing of the air-fuel mixture. The sensor consists of:

1

 - Ceramic element (ZrO

2

)

2

 - Protection tube with 3 slits

3

 - Threaded metallic body

4

 - Protection case

5

 - Electric connection

6

 - Electric element for rod heating

The functioning mode of the sensor is based upon the ceramic property of leading the

oxygen ions, at temperatures within 300 – 800 °C. The external area of the ceramic
element is in contact with the burned exhausted gases while its internal area is in contact
with the fresh air. As a consequence there will be a voltage signal between these two
ceramic areas; this signal will be transmitted to the electronic control unit (pin 9 – pin 10).
According to the size of this signal, the computer will control the ignition and injection
systems in order to obtain a value ë = 1,essential condition for catalyst operation under
optimal conditions, namely an efficient de-pollution.

The setting method in closed loop with Lambda rod is according to the following diagram:

Admission

Injector

Evacuation

Rich (poor) fuel mixture

Oxygen sensor

Computer

Reference voltage

5

4

3

1

6

2

DESCRIPTION OF THE SYSTEM

17

IGNITION AND  INJECTION

17 - 21

For starting the oxygen sensor as soon as possible after the engine start up it should be

heated by its electric resistance, type PTC = positive temperature coefficient.

The evacuation track of the burned gases should be 100% sealed in the area in front of

the  ë rod and of the catalytic converter in order to not get measurements errors of the
oxygen content in the burned gases.

Reference values:

- heating resistance of the ë rod: R

1-2

 = 1 – 15 Ù

- R insulation = R

1-4

 = R

1-3

 = R

2-3

 = R

2-4

 > 25 MÙ at 20 °C

IMPORTANT: Only fuel without lead should be supplied. Otherwise the oxygen sen-

sor and the catalyst will be broken. The oxygen sensor and the catalyst are damaged in
case of overheating caused by a difficult starting up or by an improper functioning of
the engine.

The correlation between the value ë and the dosing of the mixture is indicated in the

diagram here under.

The voltage limit values are U ë = 0.9 V for a rich mixture and U ë = 0.1 V for a poor

mixture. The value U ë = 0.45 V, existing between these two, is the reference voltage
existing in the computer memory; the later uses it in case of damage of the ë rod, the
engine being under running.

The value  ë

1

 = 1 ± 002 is the area of the voltage jump characteristic to the ceramic

element (ZrO

2

 in this case).

A voltmeter with internal resistance R

i

 = 10 MÙ

 is used for measuring the voltage generated

by the ë rod. This voltmeter will be connected to the ë rod (pins 3 and 4) or to the elec-
tronic control unit (pins 9 and 10).

Mixture

rich

Mixture

poor

DESCRIPTION OF THE SYSTEM

IGNITION AND  INJECTION

17

17 - 22

CATALYTIC CONVERTER

The catalytic converter (drawing 1, position 17) is placed on the burned gases evacuation

track between the primary down tube and the detector it is three ways type and it is used for
simultaneous transformation of the three gases existing in the evacuation gas, according to the
following chemical reactions:

C m Hn + ( m+n/4 ) O

2 

            m CO

2

 + n/2 H

2 

O

2 CO + O

2                

2CO

2

2 NO + 2 CO            N

2 

+ 2CO

2

The catalytic converter is honeycomb shaped, in ceramic, covered with a very thin film of

active catalytic substances (Platinum, Rhodium and Palladium). It accelerates the
oxidation and chemical reaction of the noxious substances existing in the evacuated burned gases.
This ceramic  structure is protected by a stainless  steel case, resisting to high
temperatures and environmental agent action.

WARNING !

Knowing that the catalytic converter reaches high temperatures during the func-

tioning it is forbidden to install it in areas storing inflammable materials – fire hazard.

In order not to damage the catalyst during a difficult engine starting, do not insist

in repetitiously trying to start the engine; pushing the vehicle it is also forbidden, one
can use a helping battery.

The engine shouldn’t run without sparking at one of its cylinders, even during test-

ing; a not burned fuel can reach and damage the catalyst.

The maximal permitted values of  the  noxious substances (vehicle technical checking):

- CO < 0,4  % vol.
- HC  < 100  ppm
- CO

 2

 > 12 % vol.

- 0,97 <

 λ < 1,03

The above mentioned formula determination is  done at an  idle rotation of  800 ± 50 rot/min

after a minimum period of 5 minutes since the engine start up (engine T = 85 – 90 °C).

DESCRIPTION OF THE SYSTEM

17

IGNITION AND  INJECTION

17 - 23

WORKING MODE

IN CASE OF INTERVENTION ON THE MONO-MOTRONIC INJECTION

SYSTEM

Prior to the engine start up one should check the correct connection of the battery; the battery

should be well loaded and its terminals should be cleaned and well tightened up.

The maximum supplying voltage of the system should not excel 15 V.
The battery should be disconnected only after stopping the engine, the contact key being on

the position “St” (contact closed).

The electronic control unit can be disconnected only after closing the contact and

disconnecting the battery terminal (-).

For checking the cylinders compression one should interrupt the power supply of the relays

(R

1

 – R

2

) of the injection system.

The ignition system should be disconnected, turning the contact key on the position “0”, prior

the interventions at the ignition system.

For instance:

- changing the engine system components
- connection to the engine tester
- connection to the checking bench

The cables in the engine compartment should be well placed in order not to be in

contact with the hot areas or with the moving parts of the engine.
In case of charging the battery form a redresser, the battery should be first disconnected from the
electric system of the vehicle.

WARNING !

1 – Only fuel without lead should be supplied, otherwise the catalytic converter will

be damaged. Use only fuel or oil additives recommended by the constructor.

2 – You should avoid bumping the catalytic converter
3 – The engine should be fit for working with the catalytic converter under normal

conditions (injection, ignition). In case of miss-ignition, supplying problems and power
losses stop the car, for avoiding the overheating of the catalytic converter; the later can
also be damaged by the too extended use of the starter in case of difficult start up.

4 – In case that fuel with lead is used by mistake, prior to changing the ë rod or the

catalytic converter one should refill the tank twice with no-lead fuel.

5 – Taking into consideration the high pressure of the fuel supplying system, all the

joints between pipes and hoses should be well tightened up with the adequate gaskets,
in order to avoid the possible fuel losses, which might lead to vehicle fire hazard.

DIAGNOSTIC