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Hit the arrow key to start!. EXPLORING COMBUSTION BEHAVIOR. SECOND EDITION. THROUGH THE EYES OF A SCOPE. by Mac VandenBrink. We know that THE OBJECTIVES OF THE COMPUTER AND SENSORS are aimed at. MAXIMUM COMBUSTION EFFICIENCY. …and it happens right here!.

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Hit the arrow key to start

Hit the arrow key to start!


Hit the arrow key to start

EXPLORING COMBUSTION BEHAVIOR

SECONDEDITION

THROUGH THE EYES OF A SCOPE

by Mac VandenBrink


We know that the objectives of the computer and sensors are aimed at

We know thatTHE OBJECTIVES OF THE COMPUTER AND SENSORSare aimed at... .

MAXIMUM COMBUSTION EFFICIENCY...

…and it happens right here!


Internal k v demand

Internal K.V demand =

ONLY

PRESSURE

& FUEL

WILL VARY

WITH RPM.

Therefore

KV demand

varies

accordingly.

HC

Variables

PRESSURE

GAP

Constant


If we must compare

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!


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Practical Application

The effect of

HC

FUEL MIXTURE

&

FUEL VOLUME


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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...


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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.


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What the scope sees!

For the first

25% 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.


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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? -


Are we ready to diagnose

Are we ready to diagnose?

WORNCAMLOBE

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.


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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


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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? -


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WORN CAMLOBE CONFIRMED!

Verify: Power performance test - low vs. high speed.


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WORN CAMLOBE CONFIRMED!

RULED OUT:

Lean fuel mixture

Low compression

CONFIRMED

Lower fuel volume

Verify: Power performance test - low vs. high speed.


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What is the SNAP-TEST?A sudden acceleration & deceleration.

Ideal objective:

When 2000 RPM is reached simultaneously with less than 4 inches vacuum.


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1

Objective of acceleration

Force the highest possible KV demand under any driving condition.

HOWOn ACCELERATION, at W.O.T., before itRPM increase, timing is still near TDC. worksThis, plus high volumetric efficiency & a lean mixture, create an extremely high KV demand.

Why?

Cross-Fire

Secondary Leakage

To reveal

any possible:

Restricted Injector


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Objective of deceleration

2

Force the lowest possible KV demand in the combustion chamber.

HOWOn DECELERATION, at closed throttle ITand high vacuum, before RPM drops, a WORKSmaximum timing advance, plus rich fuel mixture, create the lowest possible KV demand.

Why?

Excessive gap

To detect

any possible:

Open circuit

Valve seating problems


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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.


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RESTRICTED INJECTOR

Snap-test result

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.


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Practical Application

Exploring

a Misfire


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?

IS THE COMPUTER

CONTROLLING

AIR/FUEL RATIO?


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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


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Practical Application

Exploring

turbulence

etc.


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What causes turbulence

Escaping gasses passing the flame front.


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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!!


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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.


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SCORE BOARD

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


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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%. (100 RPM @ 2000)


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What have

we learned?

Follow a procedure

1. Accumulate data

2. Analyze observations

3. Diagnose problem

4. Verify diagnosis


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We learned to:

1. Accumulate data

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


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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


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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


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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.


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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.


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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.


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You have just watched a sample

of scope pattern interpretation.

What keeps you from ordering

the 90 minute video?

Available in:

DVD

VHS

Includes a 125 page

notebook.

Visit our web site: www.datec.us


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