1. Hit the arrow key to start!

2. THROUGH THE EYES OF A SCOPE
EXPLORING COMBUSTION BEHAVIOR
SECOND EDITION
THROUGH THE EYES OF A SCOPE
by Mac VandenBrink

4. …and it happens right here!
We know that THE OBJECTIVES OF THE COMPUTER AND SENSORS are aimed at
MAXIMUM COMBUSTION EFFICIENCY...
…and it happens right here!

5. Internal K.V demand = ONLY PRESSURE HC & FUEL WILL VARY WITH RPM.
Therefore
KV demand
varies
accordingly. HC
Variables
PRESSURE
GAP
Constant

6. The scope looks at fuel efficiency Plus… it does so per cylinder!
If the scan-tool looks at O2 to measure fuel efficiency, it does so after combustion is completed.
If we must compare… HC
The scope looks at fuel efficiency
before combustion,
during combustion and
after combustion
PRESSURE
GAP
Plus… it does so per cylinder!

7. Practical Application
The effect of HC
FUEL MIXTURE
&
FUEL VOLUME

8. SUPER-IMPOSED SCOPE PATTERN
THE IDEAL CONDITION...
SUPER-IMPOSED SCOPE PATTERN
Perfect conductivity from
point of ionization to
the end of the firing time. 1
Hydro-carbons are all
consumed when
the plug stops firing. 2
Fuel delivery equal
for all cylinders. 3
Let us use this as
an ideal scope pattern...

9. The not so ideal conditions...
Is this is a lean
fuel mixture?
Logical Analysis
is a process
1. Obviously a single cylinder problem.
2.Computer control problem ruled out.

10. What the scope sees! 1 2 3 4 For the first At the ionization of the
firing time,
the A.F.R.
is still normal.
At the ionization of the
pressurized gasses, the
AIR-FUEL-RATIO
was not lean. 1 2 3
This is not a lean
mixture, but rather an
absence of sufficient
hydrocarbon. 4
The coil energy is
prematurely absorbed,
due to lack of conductivity.

11. What is next? Road Test? (Customer complaint- Missing at Hi RPM.)
Look at paraded pattern?
Scope O2 sensor?
Current ramp injector?
Scope injector pattern? -
6. Cylinder balance test? -

12. Are we ready to diagnose?
WORN CAM LOBE
CLUES
Lower KV demand Why…?
Not enough HC to maintain firing...
Correct A.F.R. at start.
Verify: Power performance test - low vs. high speed.

13. What is next? Road Test? (Customer complaint- Missing at Hi RPM.)
Look at paraded pattern? DONE
Scope O2 sensor?
Current ramp injector?
Scope injector pattern? -
6. Cylinder balance test? -
DONE

14. What is next? Road Test? (Customer complaint- Missing at Hi RPM.)
Look at paraded pattern?
Scope O2 sensor?
Current ramp injector?
Scope injector pattern? -
6. Cylinder balance test? -

15. WORN CAMLOBE CONFIRMED!
Verify: Power performance test - low vs. high speed.

16. WORN CAMLOBE CONFIRMED!
RULED OUT:
Lean fuel mixture
Low compression
CONFIRMED
Lower fuel volume
Verify: Power performance test - low vs. high speed.

17. What is the SNAP-TEST? A sudden acceleration & deceleration.
Ideal objective:
When 2000 RPM is reached simultaneously with less than 4 inches vacuum.

18. Objective of acceleration1
Objective of acceleration
Force the highest possible KV demand under any driving condition.
HOW On ACCELERATION, at W.O.T., before it RPM increase, timing is still near TDC. works This, plus high volumetric efficiency & a lean mixture, create an extremely high KV demand.
Why?
Cross-Fire
To reveal
any possible:
Secondary Leakage
Restricted Injector

19. Objective of deceleration 2
Force the lowest possible KV demand in the combustion chamber.
HOW On DECELERATION, at closed throttle IT and high vacuum, before RPM drops, a WORKS maximum timing advance, plus rich fuel mixture, create the lowest possible KV demand.
Why?
Excessive gap
To detect
any possible:
Open circuit
Valve seating problems

20. Exploring the effect of
@ idle
a Snap-Test
8 KV
@ 2000 RPM
6 KV
Before the snap-test
there was no apparent problem
at low or high speed.
The objective of the snap-test is to fool the computer.

21. RESTRICTED INJECTOR NEXT CASE Snap-test result Verify @ 2000 RPM
SNAP ACCELERATION
is too fast for the fuel trim
to respond and the lean
injector is exposed.
Note the high KV demand
and the short firing time.
NEXT CASE
Verify
@ 2000 RPM
At any steady speed,
the computer is back
in control and covering
up for the lean injector.

22. Practical Application
Exploring
a Misfire

23. ?
IS THE COMPUTER
CONTROLLING
AIR/FUEL RATIO?

24. An exercise in analysis!1
@ 2000RPM
All cylinders are
driven lean except
# 3 IN F.0.
None are lean at
the start of the
spark line.
Lower KV supports
richer fuel mixture.
CONCLUSION!!!
LEAKY INJECTOR

25. Practical Application
Exploring
turbulence
etc.

26. Escaping gasses passing the flame front.
What causes turbulence
Escaping gasses passing the flame front.

27. If the evidence clearly indicates THIS IS NOT A LEAN FUEL MIXTURE…
What is pure logic telling us? 2 1
…And the scope
shows reduced
Hydrocarbon…
We must
conclude
there is also
reduced
Oxygen.
If the evidence clearly indicates
THIS IS NOT A LEAN FUEL MIXTURE…
On all
Cylinders
Conclusion… RESTRICTED EXHAUST!!

28. Allow a evaluation for each positive confirmation.
How many ways do we want
to verify a restricted exhaust?
Without dropping
the exhaust.
Without drilling
holes.
Without removing
O2 sensor.
Without a test
drive. %
Allow a evaluation for each positive confirmation.

29. SCORE BOARD 30 % ? 30 % 20 % 20 % 30 % 130 % Inhibiting EGR valve
improves performance.
30 % ?
Vacuum gauge
response sluggish.
30 %
More turbulence on
scope at high RPM.
20 %
Minimal effect on
O2 sensor.
20 %
Cylinder balance test
worse at high RPM.
30 %
130 %
CONFIRMATION

30. Explain ... Inhibiting EGR valve improves performance. What do we
expect to see?
Of course, in order to see any effect, we must be at a speed when the EGR valve is functional and that is not at idle!
If the EGR normally re-circulates about 7%, just imagine how much exhaust is dumped back into the intake with backpressure.
Temporarily inhibiting the EGR function for test purposes should not increase RPM with more than 5%. ( )

31. What have
we learned?
Follow a procedure
1. Accumulate data
2. Analyze observations
3. Diagnose problem
4. Verify diagnosis

32. We learned to: 1. Accumulate data 2. Analyze observations
Compare cylinders and isolate the odd one.
Make note of difference at low versus high RPM.
Determine at what speed is worst pattern.
Select the worst and the best cylinder.
Perform power test at that RPM on both.
Record test results on those two cylinders.
2. Analyze observations
3. Diagnose problem
4. Verify diagnosis

33. We learned to: 1. Accumulate data 2. Analyze observations
KV DEMAND - Higher - Lower - Equal.
FIRING TIME - Shorter - Longer - Turbulence -
More slope down left - More slope up right -
Good conductivity - Poor conductivity.
3. Diagnose problem
4. Verify diagnosis

34. Put all the information together and pinpoint the problem based on
We learned to:
1. Accumulate data
2. Analyze observations
3. Diagnose problem
REASON IT OUT!
Put all the information together and
pinpoint the problem based on
logical deduction.
4. Verify diagnosis

35. We learned to: 1. Accumulate data 2. Analyze observations
3. Diagnose problem
4. Verify diagnosis
PROVE YOUR POINT!
Disable injector, EGR valve or O2 sensor, etc.
Perform snap-test. Compare low & high RPM.
Enrich fuel mixture, etc.

36. at various speeds & loads. Disconnecting or disabling
Dissecting and
accumulating
information.
Analysis
Experimenting
at various speeds & loads.
Disconnecting or disabling
to observe reaction.
Conclusion
based on
analysis.
Diagnosis
Verify and qualify to
pinpoint malfunction
or component.

37. Q.C. THE Q.C ANSWERS... If this is a representation of all
cylinders superimposed, there
is no need for further diagnosis.
1. Adequate ignition to burn all the fuel.
2. Fuel delivery equal for all cylinders.
If a SNAP-TEST reveals no problem
and the O2 sensor verifies computer control,
all requirements of ignition
and combustion efficiency are met.

38. You have just watched a sample of scope pattern interpretation.
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