# Hit the arrow key to start!

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Hit the arrow key to start!

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

…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!

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

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!

Practical Application
The effect of HC FUEL MIXTURE & FUEL VOLUME

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...

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.

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.

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? -

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.

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

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? -

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

WORN CAMLOBE CONFIRMED!
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.

Objective of acceleration
1 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

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

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.

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.

Practical Application
Exploring a Misfire

? IS THE COMPUTER CONTROLLING AIR/FUEL RATIO?

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

Practical Application
Exploring turbulence etc.

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

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!!

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.

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

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%. ( )

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

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

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

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

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.

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.

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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