BRIDGWATER COLLEGE

AUTOMOTIVE SCOPE TESTING

OSCILLOSCOPE TESTER An oscilloscope is like a voltmeter. It is connected across, or in parallel, with the circuit being tested, and its most important use is to give information about voltage changes in a circuit againts time.

V O L T A G E TIME

OSCILLOSCOPE TESTER The ignition oscilloscope can have markings on it’s screen which are a number of horizontal lines, starting from 0KV and extending in increments of 5KV on the left and 10KV on the right side (secondary).

V O L T A G E TIME

OSCILLOSCOPE TESTER The screen can also be read from 0V extending in increments of 5V on the left hand side and in increments of 10V on the right hand side (primary).

The bottom of the screen is marked off in degrees and percentage.

Computer scopes may use menus for voltage and time. V O L T A G E TIME

SECONARY OSCILLOSCOPE PATTERN

SCOPE PATTERNS

SECONDARY PATTERN PURPOSE TO IDENTIFY: 1. OPEN CIRCUITS IN THE SECONDARY IGNITION CIRCUIT.

2. COMPRESSION PROBLEMS

.

3. FUEL FAULTS 4. SPARK PLUG DEFECTS 5. CONDENSER PROBLEMS 6. POINTS DEFECTS 7. ELECTRONIC IGNITION PROBLEMS

SECONDARY PATTERN 1.You are required to build up in your work book a complete diagram of a secondary ignition scope pattern.

2.Answer a number of multi-choice questions.

3.List the ignition faults against particular pictures showing incorrect secondary patterns.

SECONDARY PATTERN

FIRING LINE =

a a

SECONDARY PATTERN FIRING LINE Voltage required to establish the spark.

Normally 5 to 15 KV. Maximum variation between cylinders 3KV

SECONDARY PATTERN The required firing voltage is affected by secondary circuit gaps, cylinder compression and temperature, fuel mixture and ignition timing.

SECONDARY PATTERN

SPARKLINE

= b FIRING LINE b

SECONDARY PATTERN SPARK LINE Voltage required to maintain the spark. Max. height 3KV Max. slope 1.5KV

SECONDARY PATTERN The required spark voltage and characteristics of the spark line are affected by the secondary circuit resistance, spark plug and cylinder conditions.

SECONDARY PATTERN

COIL OSCILLATIONS =

c FIRING LINE SPARK LINE c

SECONDARY PATTERN INTERMEDIATE OSCILLATIONS Dissipation of remaining coil energy by condenser action. Normally at least 4 gradually diminishing oscillations at 2000RPM.

SECONDARY PATTERN The number of coil oscillations is affected by engine speed and defects in the coil, condenser, or primary circuit.

SECONDARY PATTERN

START OF DWELL COIL BUILDING UP IT’S MAGNETIC FIELD = d

FIRING LINE SPARKLINE d

SECONDARY PATTERN START OF DWELL The points closed signal is affected by points condition, alignment, spring tension and defects in the coil or primary circuit.

SECONDARY PATTERN Points open signal is affected by points condition and gap, or arcing due to poor condenser action, primary circuit defects or high primary current.

ELECTRONIC IGNITION Start of dwell the amplifier turns on, the end of dwell the amplifier turns off.

All modern amplifiers are fitted with

vary dwell. Vary dwell will alter the dwell angle with changes of speed, if the engine speed is low then the dwell angle is small, as the engine speed increases the dwell angle will also increase providing a constant energy ingnition system.

PRIMARY OSCILLOCOPE PATTERN

PRIMARY PATTERN Since any voltage variation in the primary ignition circuit will be reflected in secondary circuit testing, it is not always necessary to use primary circuit testing to determine the general condition of the ignition system.

The trace patterns of the primary circuit are very simular to that of the secondary. The voltage values represented in the primary patterns are much lower than the secondary patterns(primary is measured in VOLTS).

PRIMARY PATTERN The diagram below shows a single cylinder primary pattern

250V Firing section Intermediate section Dwell section

MULTI-CHOICE QUESTIONS TYPES OF OSCILLOSCOPE PATTERNS

SECONDARY PATTERN 1. STATE THE PATTERN TYPE BELOW a) Superimposed b) Single cylinder c) Raster d) Display 2. State the permitted variation between cylinders a) 8KV b) 12KV c) 3KV d) 4KV

1 3 4 2

SECONDARY PATTERN 3. NAME THE TYPE OF PATTERN BELOW a) Superimposed b) Raster c) Display

SECONDARY PATTERN 4. Name the pattern below a) Raster b) Single cylinder c) Display d) Superinposed

IGNITION SYSTEM FAULT DIAGNOSIS

SECONDARY PATTERN

MAKE A LIST AGAINST THE FOLLOWING FAULTS 1. No firing line or spark line

SECONDARY PATTERN 2. Low firing line and long spark line

3KV

SECONDARY PATTERN 3. Normal firing line and short and steep sparkline

8KV 5KV

SECONDARY PATTERN 4. High firing line short spark line

16 KV

SECONDARY PATTERN 5. Hashing when points close and open

8KV

SECONDARY PATTERN 6. Pattern is upside down

2 4 3 1

SECONDARY PATTERN 7. No 3 cylinder has a low firing line and long sparkline

2 4 3 1

SECONDARY PATTERN 8. No 4 cylinder dwell section is out of line with the other cylinders

SECONDARY PATTERN

9. Lack of coil oscillations

AUTOMOTIVE SCOPE CONNECTIONS TO VEHICLE

SCOPE CONNECTION Identify the parts of the engine the connections are made.

BOOM

a b c d e f g

SCOPE CONNECTIONS a) Red clamp to_____________ b) Chrome clamp to___________ c) Green clip to_______________ d) Yellow clip to______________ e) Black clip to_______________ f) Red clip to_________________ g) Green clamp to____________