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

Hit the arrow key
to start!
EXPLORING
COMBUSTION
BEHAVIOR
THROUGH THE
EYES OF A SCOPE
We know that
THE OBJECTIVES OF THE
COMPUTER AND SENSORS
are aimed at...
.
…and it happens right here!
Internal K.V demand =
HC
Variables
PRESSURE
GAP
Constant
ONLY
PRESSURE
& FUEL
WILL VARY
WITH RPM.
Therefore
KV demand
varies
accordingly.
If we must compare…
HC
PRESSURE
GAP
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!
SUPER-IMPOSED SCOPE PATTERN
Perfect conductivity from
point of ionization to
the end of the firing time.
Hydro-carbons are all
consumed when
the plug stops firing.
Fuel delivery equal
for all cylinders.
Is this is a lean
fuel mixture?
1. Obviously a single cylinder problem.
2.Computer control problem ruled out.
For the first
25% of the
firing time,
the A.F.R.
is still normal.
This is not a lean
mixture, but rather an
absence of sufficient
hydrocarbon.
At the ionization of the
pressurized gasses, the
AIR-FUEL-RATIO
was not lean.
The coil energy is
prematurely absorbed,
due to lack of conductivity.
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 weCAM
readyLOBE
to diagnose?
WORN
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.
1. Road Test? (Customer complaint- Missing at Hi RPM.)
2. Look at paraded pattern? DONE
DONE
3. Scope O2 sensor?
4. Current ramp injector?
5. Scope injector pattern? 6. Cylinder balance test? -
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.
RULED OUT:
Lean fuel mixture
Low compression
CONFIRMED
Lower fuel volume
Verify: Power performance test - low vs. high speed.
What is the
SNAP-TEST?
A sudden acceleration &
deceleration.
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
it
works
On ACCELERATION, at W.O.T., before
RPM increase, timing is still near TDC.
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
IT
WORKS
On DECELERATION, at closed throttle
and high vacuum, before RPM drops, a
maximum timing advance, plus rich fuel
mixture, create the lowest possible
KV demand.
@ idle
@ 2000 RPM
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.
Snap-test result
NEXT CASE
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.
Verify @ 2000 RPM
At any steady speed,
the computer is back
in control and covering
up for the lean injector.
All cylinders are
driven lean except
# 3 IN F.0.
@ 2000RPM
None are lean at
the start of the
spark line.
Lower KV supports
richer fuel mixture.
CONCLUSION!!!
Escaping gasses
passing the flame front.
…And the scope
shows reduced
Hydrocarbon…
If the evidence clearly indicates
THIS IS NOT A LEAN FUEL MIXTURE…
We must
conclude
there is also
reduced
Oxygen.
Conclusion… RESTRICTED EXHAUST!!
Without dropping
the exhaust.
Without drilling
holes.
Without removing
O2 sensor.
Without a test
drive.
Allow a
evaluation for each positive confirmation.
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 %
CONFIRMATION
130 %
Inhibiting EGR valve What do we
improves performance. 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)
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 on
logical 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.
Experimenting
at various speeds & loads.
Disconnecting or disabling
to observe reaction.
Conclusion
based on
analysis.
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 problem
and the O2 sensor verifies computer control,
all requirements of ignition
and combustion efficiency are met.
You have just watched a sample
of scope pattern interpretation.