Holden Engine Troubleshooter. Reference Manual

PAGE 33

H014 V6 Direct Fire Ignition (DFI) Power Balance Testing

Power Balance Testing

You can do a power balance test on a direct ignition system by using short lengths of vacuum

hose and a 12-volt test lamp. The vacuum hose must have a high carbon content so that it

will conduct secondary voltage. Install a short piece of hose between each coil terminal and

its spark plug cable as per figure 1.
The vacuum hose should be long enough to be exposed when the plug cable is connected

but short enough that they do not touch any metal object.

Using a 12-volt test lamp connected to ground, touch each vacuum hose to short the cylinder.

Note the engine speed as you short each cylinder. Then slowly move the test lamp probe

away from the hose and note the strength of the arc between the vacuum hose and the

test lamp probe. As with any power balance test, engine speed will decrease the least on

a cylinder with a problem. Interpret the strength of the arc between the hose and the lamp

probe as follows:
Touch the vacuum hoses with the test lamp until you find little or no rpm drop. Then move the

probe away from the hose and note the arc. If the arc jumps a long distance to the grounded

test lamp, suspect an open circuit between the coil and the plug. Look for an open plug

cable or plug or a very wide plug gap. If the arc jumps only a short distance to the grounded

test lamp, suspect a short circuit between the coil and the plug. Look for a shorted cable or

plug, or a fouled, cracked, or carbon tracked spark plug, figure 2.

Broken Spark Plug Insulator

The ceramic spark plug insulator can break near the base where it is hard to see, figure 15.

This can cause a misfire. You may need to gently tap on the spark plug. If the insulator slides

down, it will mask the spark, causing a misfire. You can also check the resistance between

the terminal and the centre electrode. Typically, the resistance should be 6000 ohms or less.

A defective plug will often show an open circuit or high resistance.

Figure 1: Vacuum hose connection for power balance testing.

Figure 2: Spark Plug Insulation.

PAGE 34

H015 Fuel System Diagnosis Using Fuel Pump Current

Knowing whether a running fuel pump is drawing too much or too little current can help you

identify a faulty fuel system component.

To measure fuel pump current, you can use an ammeter or a DMM with an inductive probe.

WARNING: High current flowing through faulty fuel pump circuits may damage a DMM. Do not

use a measuring tool whose current-rating is less than the current you expect to measure.

If using an ammeter, remove the fuel pump fuse and connect the leads across the fuel

terminals. If only using an inductive probe, attach its end around the positive feed wire to the

fuel pump.

With the test leads or probe hooked up, start and run the engine if possible. If trouble-shooting

an intermittent problem, allow the engine to run long enough to give the fault an opportunity

to present itself. Then record the key-on engine-running fuel pump current. Turn the ignition

switch to the OFF position and back to the ON position without restarting the vehicle. After

the fuel pump stops running (usually about 2 seconds), record the current again. Normally

this nominal current is 0 to 0.7 amps.

If the problem affecting the vehicle prevents you from starting the engine, turn the key to the

ON position. Record the key-on engine-off current before the fuel pump stops running. Turn the

ignition switch to the OFF position and back to the ON position without restarting the vehicle.

After the fuel pump stops running (usually about 2 seconds), record the nominal current.

Subtract the nominal current from the key-on engine-off or key-on engine-running current to

obtain the fuel pump current draw. Refer to table 1 to see if the current draw value falls within

specification.

If the fuel pump current is much lower than specification, suspect:

• empty fuel tank

• an open pump circuit

• a damaged pulsator (dampener)

• a leaking internal connection between the pump and fuel line

• a broken pressure regulator spring

• a faulty fuel pump

If the fuel pump current is much greater than specification, suspect a:

• plugged fuel filter

• restricted fuel hose

• faulty fuel pump

Fuel Pump Priming Operation

When the ignition is turned on, the PCM for GM fuel injection systems energizes the fuel pump

for about 2 seconds to prime the system. If the PCM does not get a tach (cranking) signal

within the 2 seconds, it de-energizes the pump relay, figure 3. When cycling the ignition to

pressurise the system for testing, leave the ignition off for 15 seconds before turning it on

again; or the PCM will not re-energize the pump relay.

Note these systems hold residual pressure when the engine is off. Pressure can leak down,

however, during a long engine-off period.

PAGE 36

H016 continued

•

Verify that the module and the sensors all have good grounds. Refer to diagrams for
terminal identification.

•

If the engine does not start, tap the crank sensor lightly with a screwdriver handle. If
the engine then starts, the sensor may have an intermittent open or short circuit.

You can use the Vantage Meter, an oscilloscope, a digital volt-ohmmeter (DVOM), or a
light-emitting diode (LED) test lamp to check the sensor signal. Connect test equipment
as shown in Figure 2. Set the scope for a 20-millisecond (20 ms) sweep and 5.0 volts per
division. The scope display for a good sensor should be similar to the patterns previously
shown in Figure 1.

•

1X and 3X Signals – Check these signals with either a DVOM, LED test lamp, or a
scope. Leave the sensor connected and backprobe the correct terminals at the ignition
module; then crank the engine. DVOM dc voltage will fluctuate if the sensor is working.
An LED will flash as the signal voltage goes high and low and actually provides a better
indication than a DVOM.

•

18X Signal – This signal is too fast to check reliability with a DVOM or an LED. A scope
provides the most reliable reading. As an alternative, set a DVOM on the 20- or 40- volt
scale and connect the positive (+) lead to a battery positive (+) voltage. Backprobe
the sensor signal terminal at the module with the DVOM negative (–) lead. Turn the
ignition on and bump the starter; do not crank the engine steadily. The DVOM reading
should be high (above 9 volts) when a blade of the interrupter ring is in the sensor
slot (window closed) and low (below 3 volts) when the blade is out of the slot (window
open). It may take several tries to alternately position a blade in and out of the sensor
slot and verify the high and low signal voltage levels.

PAGE 37

H017 Integrator and Block Learn Functions

The integrator and black learn functions are responsible for making minor adjustments to
the air-fuel mixture on fuel injected vehicles. The integrator makes temporary, short-term
corrections, while block learn makes more permanent, long-term corrections. Integrator and
block learn give useful diagnostic values only when the car is running in closed loop.

Integrator

The integrator monitors the oxygen sensor output voltage and adds or subtracts fuel,
depending on the lean or rich condition of the O2 sensor. Think of the integrator value as
representing injector on time, the larger the number, the more fuel delivered. Even though
integrator values go from 0 to 255, typically a low number would be 58 and a high number
would be 198.

Block Learn

Block learn monitors the integrator value and compares it to engine operating ranges at various
combinations of rpm and load. Load is determined by engine speed and MAP. A plot of rpm
versus engine load is used to determine the performance boundaries. These performance
boundaries are called cells or blocks. VN and VP models have 16 different cells.

The PCM has different fuel delivery values stored in each block. Block 0 is idle with no load,
and block 15 is maximum rpm and maximum load. As the operating range changes to a
different block, the fuel delivery changes to the operating value stored in that block.

If the integrator is far enough from 128, the PCM changes the block learn value. Once the
block learn value is changed, it should force the integrator back to 128. If the mixture is still
not correct, based on the O2 sensor, the integrator will continue to have a large division from
128 and the block learn value will continue to change until the integrator value becomes
balanced.

When integrator increases or decreases, block learn responds by making changes in the
same direction. As block learn makes its long-term corrections, the need for the integrator
short-term correction is reduced. In a properly operating system, integrator will adjust the
fuel mixture until block learn takes over, and then integrator will return to its normal value
of 128.

Both the integrator and block learn have limits that vary, depending on the vehicle. Once a
problem exceeds the block learn correction limit, the integrator goes to its correction limit,
and the check engine lamp will light.

Block Learn Memory Storage

The values stored in the block learn cells remain in memory when the ignition is turned OFF.
Upon restart, the fuel delivery for a given block is based on the stored value. Disconnecting
the battery or power supply to the PCM will cause the fuel trim memory to be lost.

PAGE 38

H017 continued

Using Block Learn and Integrator To Find Vacuum Leaks

A block learn value that is high at idle, and normal at 3000 rpm, indicates a possible vacuum
leak. This is because a vacuum leak is a larger percentage of total air flow at idle than at
3000 rpm. Thus, the fuel mixture needs more correction at idle.

Integrator can help you find a vacuum leak. Pinch off the vacuum hoses as close as possible
to the intake manifold while observing the integrator value. A sudden drop in the reading
while pinching a hose indicates a vacuum leak in that hose, or an attached component.

Using Block Learn To Diagnose Fuel Flow Problems

A block learn value that is normal at idle and high at 3000 rpm indicates a possible fuel flow
problem. This is because the engine needs more fuel at 3000 rpm than at idle. Thus, the fuel
mixture needs more correction at high rpm. Suspect a dirty fuel filter or a weak fuel pump.

A block learn value that is high at both idle and 3000 rpm indicates dirty fuel injectors, or
low fuel pressure. This is because fuel injector flow and fuel pressure affects the engine at
all rpm.

Using Block Learn To Diagnose A Rich Condition

A block learn reading that is low at idle – 100 or below – or low at 3000 rpm indicates a
rich condition. Possible areas of concern at fuel-contaminated oil, a leaking fuel pressure
regulator, a leaking fuel injector, or high fuel pressure.

PAGE 39

H018 Short Term and Long Term Fuel Trim Functions

The short term fuel trim (STFT) and long term fuel trim (LTFT) functions are responsible for
making minor adjustments to the air-fuel mixture on fuel injected vehicles. The STFT makes
temporary, short-term corrections, while LTFT makes more permanent, long-term corrections.
LTFT and STFT give useful diagnostic values only when the car is running in closed loop.

Short Term Fuel Trim

The STFT monitors the oxygen sensor output voltage and adds or subtracts fuel, depending
on the lean or rich condition of the O2 sensor. Think of the STFT value as representing
injector on time, value above 0%, the more fuel delivered. Even though STFT values go
from -100% to +100%, typically a low number would be less than -20% and a high number
would above 25%.

Long Term Fuel Trim

LTFT monitors the STFT value and compares it to engine operating ranges at various
combinations of rpm and load. Load is determined by engine speed and MAP. A plot of rpm
versus engine load is used to determine the performance boundaries. These performance
boundaries are called cells or blocks. VR and VS models have 24 and VT models onwards
have 34 different cells.

The PCM has different fuel delivery values stored in each cell. As the operating range changes
to a different cell, the fuel delivery changes to the operating value stored in that cell.

If the STFT is far enough from 0%, the PCM changes the LTFT value. Once the LTFT value
is changed, it should force the STFT back to 0%. If the mixture is still not correct, based on
the O2 sensor, the STFT will continue to have a large division from 0% and the LTFT value
will continue to change until the STFT value becomes balanced.

When STFT increases or decreases, LTFT responds by making changes in the same direction.
As LTFT makes its long-term corrections, the need for the STFT short-term correction is
reduced. In a properly operating system, STFT will adjust the fuel mixture until STFT takes
over, and then STFT will return to its normal value of 0%.

Both the STFT and LTFT have limits that vary, depending on the vehicle. Once a problem
exceeds the LTFT correction limit, the STFT goes to its correction limit, and the check engine
lamp will light.

LTFT Memory Storage

PAGE 41

H019 3.8 Litre V6 Ignition Test

This test requires the use of 3 paper clips, 2 straightened for probing and earthing and 1 bent

to a narrow “U” shape for bridging. The use of Snap-on part number MT3000430A5R back

probes are recommended for probing but paperclips can be used if not available. Be careful

not to allow any probes to touch or earth out.

Follow test as follows:

With ignition OFF and DFI module 14-pin connector disconnected, bridge connector

terminals N (white/black) and P (VN pre-Oct 89 pink/VN post-Oct 89, VP, VR, VS

red/VT onwards green).

b) Insert probe into connector terminal M (grey/red) and connect it to earth.

Probe connector terminal H (blue/white) with a testlight which is connected to 12V

positive.

d) Switch ignition on and slowly turn engine over by hand (28mm socket). Check if

testlight goes ‘on’ and ‘off’ as 3X interrupter blades pass through crank sensor. If

testlight goes ‘on’ and ‘off’ go to tip 2. If not check for continuity and no shorts of

white/black, blue/white and grey/red wires from DFI connector to crank sensor. If

wiring is okay then suspect crank sensor.

Switch ignition off

b) Remove testlight probe from connector terminal H (blue/white) and insert probe

into connector terminal G (blue/yellow).

Switch ignition on and slowly turn engine over by hand. Testlight should go ‘on’

and ‘off’ as 18x interrupter ring passes through crank sensor.

If testlight goes ‘on’ and ‘off’ go to tip 3.

If not, check for continuity and no shorts of blue/yellow wire from crank sensor to

DFI module pin G. If wiring okay, suspect faulty crank sensor.

Switch ignition off and remove all leads and refit 14-pin connector to DFI module.

b) Remove coil packs from top of DFI module including the terminals on base of

coils.

Fit testlight across corresponding coil terminals from DFI module.

d) With engine cranking, testlight should blink. This test should be done across all

three corresponding coil DFI terminals.

If testlight blinks across all three, go to tip 4.

If testlight did not blink across any one of the DFI terminals the suspect faulty DFI

module.

PAGE 42

H019 continued

a) Check coil primary resistance by using an ohmmeter across the underside

corresponding terminals of each coil. Reading should be 0.30 ohms to 1.5 ohms
across all these primary terminals of coils.

If reading is okay, go to tip 5.

If reading is out, suspect faulty ignition coil.

b) Check coil secondary resistance by using an ohmmeter across the corresponding

plug lead posts of all three ignition coils.

If combined coil pack (pre-1999)

If separate coil packs (post-1990)

reading should be

10 Kohms to 14 Kohms

5 Kohms to 7 Kohms

If any coil is out of range or if one coil differs from other two by more than 1 Kohm,

then suspect faulty coil.

If all tests pass and ignition tests and plugs are okay, this indicates ignition system

should operate. Check for poor connections etc for possible cause of intermittent
fault.

NOTE: After test when components are reinstalled, switch ignition ON and reinput

back to previous Scanner menu selection screen to continue with tip.

PAGE 43

H020 Intake Air Tempterature (IAT) and

Manifold Air Temperature (MAT) Sensor

Resistance to Temperature Values

3.8 Litre V6 Models

VN, VP & VR Models

VS, VT, VX & VY Models

5.0 Litre V8 Models

All Models

°C

OHMS

100

185

450

1,800

3,400

7,500

-7

13,500

-18

25,000

-40

100,700

°C

OHMS

°C

OHMS

-40

102,129

679

-35

73,345

566

-30

53,253

475

-25

39,066

400

-20

28,940

338

-15

21,638

287

-10

16,321

245

-5

12,414

210

9,517

100

180

7,355

105

156

5,729

110

135

4,497

115

117

3,555

120

102

2,830

125

2,268

130

1,829

135

1,483

140

1,210

145

993

150

819

°C

OHMS

100

185

450

1,800

3,400

7,500

-7

13,500

-18

25,000

-40

100,700

PAGE 44

H021 VS & VT 3.8 Litre V6 Knock Sensor Test

With ignition off disconnect PCM connectors.

Check resistance of PCM connector pin C12 (white/red) to ground.

If reading approx. 50 Kohms go to step 4.

If reading approx. 100 Kohms go to step 3.

If reading not 50 Kohms or 100 Kohms check wiring from PCM connector pin C12
(white/red) to knock sensors for open or short. If wiring is okay then suspect faulty
knock sensors.

If reading was 100 Kohms then one knock sensor or wiring to one knock sensor has
open circuit. Remove connector from knock sensors and check centre knock sensor
terminal to ground resistance to see if one is open. If knock sensors are not open, trace
open in wiring from PCM connector pin C12 (white/red) to one knock sensor connector
and repair as needed.

If reading was 50 Kohms reconnect PCM connectors. With digital voltmeter set on
AC voltage backprobe PCM connector pin C12 (white/red) with +ve lead and -ve to
ground. Top alternator bracket with hammer while observing reading. If reading always
less than 50mV AC then suspect faulty knock sensors. If reading goes over 50mV AC
then suspect intermittent fault. Check all connectors.

NOTE: After test when components are reinstalled, switch ignition on and reinput back
to previous Scanner menu selection screen to continue with tip.

PAGE 46

H023 5.0 Litre V8 Coil Resistance Check

H024 3.8 Litre V6 Coil Resistance Check

Primary resistance across +ve and -ve of coil terminals 0.76 to 0.84 ohms.

Secondary resistance across -ve coil terminal and high tension post 4.5 Kohms to 6.0
Kohms.

Always check for cracks in coil casing particularly near mounting bracket.

After testing, reinstall components and switch ignition on to continue using the
Troubleshooter.

NOTE: If any coil out of range or if one coil secondary reading differs from other two by more
than 1 Kohm then suspect faulty coil.

After testing, reinstall components and switch ignition on to continue using the
Troubleshooter.

One piece combined

Individual

coil pack type

Primary resistance checked

0.3 ohm to 1.5 ohm

across corresponding terminals
on underside of coil

Secondary resistance

10 Kohm to 14 Kohm

5 Kohm to 7 Kohm

checked across correponding
high tension posts

Holden Engine Troubleshooter. Reference Manual - part 3