Isuzu KB P190. Manual - part 818

Engine Management – V6 – General Information 

Page 6C1-1–30 

 

Similar to the two-step HO2S, measurement is achieved by 
comparing the oxygen content of the exhaust gas to the 
oxygen content of a reference gas. However, the way in 
which the ECM calculates the exhaust oxygen content is 
different, and results in a continual signal. This allows the 
ECM to monitor not only whether the fuel mixture is rich or 
lean, but exactly how rich or how lean. The wide-band 
HO2S is basically a two-step HO2S with the addition of a 
pump cell. 

The ECM applies a pump voltage across the pump cell, 
which causes oxygen to be pumped from the exhaust gas 
into or out of the diffusion gap through the diffusion barrier. 
While monitoring the Nernst cell, the ECM varies the pump 
current so the gas in the diffusion gap remains constant at 
an A/F ratio of 14.7:1 (Nernst cell output of 450 mV).  

Legend 

1 Outer 

Electrode 

2 Inner 

Electrode 

3 Heater 

Element 

4 

Oxygen Molecule (in exhaust stream) 

5 

Other Molecules (in exhaust stream) 

6 

Reference Gas (outside air) 

7 Nernst 

Cell 

8 

Pump Cell Electrode 

9 

Pump Cell Electrode 

10 

Pump Cell  

11 Diffusion 

Gap 

12 

Porous Diffusion Barrier 

A Pump 

Current 

V 

Nernst Cell Voltage 

Figure 6C1-1 – 36 

If the exhaust gas is lean, the pump cell pumps oxygen to 
the outside (positive pump current). If the exhaust gas is 
rich, oxygen is pumped from the exhaust gas into the 
diffusion gap (negative pump current). By monitoring how 
much it has to vary the pumping current, the ECM 
determines the exact A/F ratio. 

Legend 

A Rich 

Mixture 

B 

A/F Ratio 14.7:1 (Lambda = 1) 

C Lean 

Mixture 

D Sensor 

Current 

Figure 6C1-1 – 37 

Engine Management – V6 – General Information 

Page 6C1-1–31 

 

4.15  Ignition Coil and Spark Plug 

Long-life platinum tip spark plugs are used which, along with 
the ignition coil spark plug boot and spring, require 
replacement at 100,000 kilometre service intervals. The 
spark plugs, featuring a J-gap and a conical seat, do not 
require inspection between services, and must not be re-
gapped. 

Individual pencil-type ignition coils, one for each cylinder, are 
mounted in the centre of the camshaft covers, and have 
short boots connecting the coils directly to the spark plugs. 

The pencil coil makes use of the space available in the spark 
plug cavity in the cylinder head and camshaft cover. As a 
pencil coil is always mounted directly on to the spark plug, 
no high-tension ignition leads are required, further enhancing 
reliability. 

 

Figure 6C1-1 – 38 

Pencil coils operate similarly to other compact coils, however 
due to their shape, the structure differs considerably. 

The central rod core (1) consists of laminations of varying 
widths, stacked in packs that are nearly spherical. A yoke 
plate (2), made from layered electrical sheet steel, provides 
the magnetic circuit. The primary winding (3) is located 
around the secondary winding (4), which supports the core.

A printed circuit board, or driver module, (5) is located at the 
top of the coil and controls the firing of the coil based on 
input from the ECM. 

The ECM is responsible for maintaining correct spark timing 
and dwell for all driving conditions. The ECM calculates the 
optimum spark parameters from information received from 
the various sensors, and triggers the appropriate ignition 
module which then operates the coil. 

The ignition coil / modules are supplied with the following 
circuits: 

• 

Ignition feed circuit. 

• 

Ground circuit. 

• 

Ignition control circuit. 

• 

Reference low circuit. 

 

Figure 6C1-1 – 39 

Engine Management – V6 – General Information 

Page 6C1-1–32 

 

4.16  Intake Air Temperature Sensor 

The intake air temperature (IAT) sensor is a thermistor, 
which is a resistor that changes it’s resistance value based 
on temperature. 

The IAT sensor is part of the air mass sensor and is not a 
serviceable item. The sensor is a negative temperature 
coefficient (NTC) type, intake air temperature produces a 
high sensor resistance while high engine coolant 
temperature causes low sensor resistance. 

Legend 

A Temperature 

B Resistance 

The ECM provides a 5 V reference signal to the IAT and 
monitors the return signal which enables it to calculate the 
intake air temperature. 

The ECM uses this signal to make corrections to the 
operating parameters of the system based on changes in air 
intake temperature. 

Figure 6C1-1 – 40 

4.17 Knock 

Sensor 

The knock sensor (KS) signal is used by the ECM to provide 
optimum ignition timing while minimising engine knock or 
detonation. 

The ECM monitors the voltage of the left-hand (Bank 2) 
sensor during the 45 degrees after cylinder 2, 4, or 6 has 
fired and the voltage of the right-hand (Bank 1) sensor 
during the 45 degrees after cylinder 1, 3, or 5 has fired. 

If knock occurs in any of the cylinders, the ignition will be 
retarded by three degrees for that particular cylinder. If the 
knocking then stops, the ignition will be restored to what it 
was before in steps of 0.75 degrees. 

Should knocking continue in the same cylinder despite of 
the ignition being retarded, the ECM will retard the ignition 
an additional step of three degrees, and so on, up to a 
maximum of 12.75 degrees. The ignition will also be 
retarded at high ambient temperatures to counteract 
knocking tendencies provoked by high intake air 
temperatures. 

Should either Bank 1 or Bank 2 sensor fail to work, or 
should an open circuit occur, the ignition timing will then be 
set at a default strategy that will retard the ignition much 
more than normal. 

Figure 6C1-1 – 41 

Engine Management – V6 – General Information 

Page 6C1-1–33 

 

The knock sensor is tuned to detect the frequency of the 
vibration created by combustion knock. The vibration is 
transferred to the knock sensor through the cylinder 
block (1). 

Inside the sensor is a mass (2) that is excited by this 
vibration, and the mass exerts a compressive force onto a 
piezo-ceramic element (3). The compressive force causes a 
charge transfer inside the element, so that an AC voltage 
appears across the two outer faces (4) of the element. The 
amount of the AC voltage produced is proportional to the 
amount of knock. 

Figure 6C1-1 – 42 

4.18  Mass Air Flow Sensor 

Air Intake System 

The air intake system draws outside air through an air 
cleaner assembly (1). The air is then routed through a mass 
air flow (MAF) sensor (2) and into the throttle body and 
intake manifold. The air is then directed into the intake 
manifold runners, through the cylinder heads and into the 
cylinders. 

An arrow marked on the body of the MAF sensor indicates 
correct air flow direction. The arrow must point toward the 
engine. 

Figure 6C1-1 – 43 

Mass Air Flow Sensor 

A hot film type mass air flow (MAF) sensor is used which 
measures the air mass inducted into the engine, regardless 
of the engine’s operating state. The MAF precisely 
measures a portion of the total airflow and takes into 
account the pulsation and reverse flows generated by the 
engine’s inlet and exhaust valves. 

Changes in intake air temperature have no effect on 
measuring accuracy. 

Figure 6C1-1 – 44