Hit the arrow key to start! EXPLORING COMBUSTION BEHAVIOR THROUGH THE EYES OF A SCOPE SECOND EDITION

Hit the arrow key to start!

EXPLORING COMBUSTION BEHAVIOR

THROUGH THE EYES OF A SCOPE

SECOND EDITION

SECOND EDITION

We know thatTHE OBJECTIVES OF THE

COMPUTER AND SENSORSare aimed at... .

MAXIMUM

COMBUSTION

EFFICIENCY...

…and it happens right here!

GAPGAP

PRESSUREPRESSURE

HCHC

Internal K.V demand =

ONLY PRESSURE

& FUELWILL VARYWITH RPM.Therefore

KV demandvaries

accordingly.Constant

Variables

GAPGAP

PRESSUREPRESSURE

HCHC

If we must compare… If the scan-tool looks at O2 to measure fuel efficiency, it

does so after combustion is

completed.

The scope looks at fuel efficiency

before combustion,during combustion

and after combustion

Plus… it does so per cylinder!

Fuel delivery equal for all cylinders.

Perfect conductivity from point of ionization to

the end of the firing time.

Hydro-carbons are all consumed when

the plug stops firing.

SUPER-IMPOSED SCOPE PATTERN

Is this is a lean fuel mixture?

1. Obviously a single cylinder problem.

2.Computer control problem ruled out.

At the ionization of the pressurized gasses, the

AIR-FUEL-RATIO was not lean.

For the first25% of thefiring time,the A.F.R.

is still normal.

The coil energy is prematurely absorbed,

due to lack of conductivity.

This is not a leanmixture, but rather an absence of sufficient

hydrocarbon.

1. Road Test? (Customer complaint- Missing at Hi RPM.)

2. Look at paraded pattern?

3. Scope O2 sensor?

4. Current ramp injector?

5. Scope injector pattern? -

6. Cylinder balance test? -

Are we ready to diagnose?WORN CAM LOBE

CLUESCLUES

Correct A.F.R. at start.

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

Lower KV demand Why…?

Not enough HC to maintain firing...

1. Road Test? (Customer complaint- Missing at Hi RPM.)

2. Look at paraded pattern? DONE

3. Scope O2 sensor?

4. Current ramp injector?

5. Scope injector pattern? -

6. Cylinder balance test? -

DONE

1. Road Test? (Customer complaint- Missing at Hi RPM.)

2. Look at paraded pattern?

3. Scope O2 sensor?

4. Current ramp injector?

5. Scope injector pattern? -

6. Cylinder balance test? -

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

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

RULED OUT:Lean fuel mixtureLow compression

CONFIRMEDLower fuel volume

What is the What is the

SNAP-TEST?SNAP-TEST?

A sudden acceleration & A sudden acceleration & deceleration.deceleration.

Ideal objective:

When 2000 RPM is reached simultaneously with less than

4 inches vacuum.

Ideal objective:

When 2000 RPM is reached simultaneously with less than

4 inches vacuum.

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.

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.

@ idle

@ 2000 RPM

8 KV

6 KV

The objective of the snap-test is to fool the computer.

Before the snap-testthere was no

apparent problem at low or high speed.

NEXT CASE

SNAP ACCELERATIONis too fast for the fuel trim to respond and the lean

injector is exposed.Note the high KV demandand the short firing time.

Snap-test result

At any steady speed, the computer is back

in control and coveringup for the lean injector.

@ 2000 RPMVerify

All cylinders aredriven lean except

# 3 IN F.0.

None are lean atthe start of the

spark line.

Lower KV supportsricher fuel mixture.

CONCLUSION!!!

@ 2000RPM

Escaping gasses passing the flame front.

Conclusion… RESTRICTED EXHAUST!!

…And the scopeshows reducedHydrocarbon…

We must conclude

there is alsoreduced Oxygen.

If the evidence clearly indicatesTHIS IS NOT A LEAN FUEL MIXTURE…

On all

Cylinders

Without dropping the exhaust.

Without drilling holes.

Without removing O2 sensor.

Without a test drive.

Allow a evaluation for each positive confirmation.

Vacuum gaugeresponse sluggish.

More turbulence onscope at high RPM.

Cylinder balance test worse at high RPM.

Inhibiting EGR valveimproves performance.

30 %

Minimal effect onO2 sensor.

30 %

30 %

20 %

20 %

130 % CONFIRMATION

Inhibiting EGR valveimproves performance.

What do weexpect 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)

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.

KV DEMAND - Higher - Lower - Equal.

FIRING TIME - Shorter - Longer - Turbulence -More slope down left - More slope up right -

Good conductivity - Poor conductivity.

REASON IT OUT!Put all the information together and

pinpoint the problem based onlogical deduction.

PROVE YOUR POINT!Disable injector, EGR valve or O2 sensor, etc.Perform snap-test. Compare low & high RPM.

Enrich fuel mixture, etc.

Dissecting and accumulating

information.

Conclusionbased on analysis.

Experimenting at various speeds & loads.

Disconnecting or disablingto observe reaction.

Experimenting at various speeds & loads.

Disconnecting or disablingto observe reaction.

Verify and qualify to pinpoint malfunction

or component.

Verify and qualify to pinpoint malfunction

or component.

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 problemand the O2 sensor verifies computer control,

all requirements of ignitionand combustion efficiency are met.

Includes a 125 page

notebook.

You have just watched a sample of scope pattern interpretation.