4…and it happens right here! We know that THE OBJECTIVES OF THE COMPUTER AND SENSORS are aimed atMAXIMUM COMBUSTION EFFICIENCY...…and it happens right here!
5Internal K.V demand = ONLY PRESSURE HC & FUEL WILL VARY WITH RPM. ThereforeKV demandvariesaccordingly.HCVariablesPRESSUREGAPConstant
6The 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…HCThe scope looks at fuel efficiencybefore combustion,during combustion andafter combustionPRESSUREGAPPlus… it does so per cylinder!
7Practical Application The effect ofHCFUEL MIXTURE&FUEL VOLUME
8SUPER-IMPOSED SCOPE PATTERN THE IDEAL CONDITION...SUPER-IMPOSED SCOPE PATTERNPerfect conductivity frompoint of ionization tothe end of the firing time.1Hydro-carbons are allconsumed whenthe plug stops firing.2Fuel delivery equalfor all cylinders.3Let us use this asan ideal scope pattern...
9The not so ideal conditions... Is this is a leanfuel mixture?Logical Analysisis a process1. Obviously a single cylinder problem.2.Computer control problem ruled out.
10What 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 thepressurized gasses, theAIR-FUEL-RATIOwas not lean.123This is not a leanmixture, but rather anabsence of sufficienthydrocarbon.4The coil energy isprematurely absorbed,due to lack of conductivity.
11What 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? -
12Are we ready to diagnose? WORN CAM LOBECLUESLower KV demand Why…?Not enough HC to maintain firing...Correct A.F.R. at start.Verify: Power performance test - low vs. high speed.
13What is next? Road Test? (Customer complaint- Missing at Hi RPM.) Look at paraded pattern? DONEScope O2 sensor?Current ramp injector?Scope injector pattern? -6. Cylinder balance test? -DONE
14What 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? -
15WORN CAMLOBE CONFIRMED! Verify: Power performance test - low vs. high speed.
16WORN CAMLOBE CONFIRMED! RULED OUT:Lean fuel mixtureLow compressionCONFIRMEDLower fuel volumeVerify: Power performance test - low vs. high speed.
17What is the SNAP-TEST? A sudden acceleration & deceleration. Ideal objective:When 2000 RPM is reached simultaneously with less than 4 inches vacuum.
18Objective of acceleration 1Objective of accelerationForce 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-FireTo revealany possible:Secondary LeakageRestricted Injector
19Objective 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 gapTo detectany possible:Open circuitValve seating problems
20Exploring the effect of @ idlea Snap-Test8 KV@ 2000 RPM6 KVBefore the snap-testthere was no apparent problemat low or high speed.The objective of the snap-test is to fool the computer.
21RESTRICTED INJECTOR NEXT CASE Snap-test result Verify @ 2000 RPM SNAP ACCELERATIONis too fast for the fuel trimto respond and the leaninjector is exposed.Note the high KV demandand the short firing time.NEXT CASEVerify@ 2000 RPMAt any steady speed,the computer is backin control and coveringup for the lean injector.
26Escaping gasses passing the flame front. What causes turbulenceEscaping gasses passing the flame front.
27If the evidence clearly indicates THIS IS NOT A LEAN FUEL MIXTURE… What is pure logic telling us?21…And the scopeshows reducedHydrocarbon…We mustconcludethere is alsoreducedOxygen.If the evidence clearly indicatesTHIS IS NOT A LEAN FUEL MIXTURE…On allCylindersConclusion… RESTRICTED EXHAUST!!
28Allow a evaluation for each positive confirmation. How many ways do we wantto verify a restricted exhaust?Without droppingthe exhaust.Without drillingholes.Without removingO2 sensor.Without a testdrive.%Allow a evaluation for each positive confirmation.
30Explain ... 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%. ( )
32We 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 observations3. Diagnose problem4. Verify diagnosis
33We 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 problem4. Verify diagnosis
34Put all the information together and pinpoint the problem based on We learned to:1. Accumulate data2. Analyze observations3. Diagnose problemREASON IT OUT!Put all the information together andpinpoint the problem based onlogical deduction.4. Verify diagnosis
35We learned to: 1. Accumulate data 2. Analyze observations 3. Diagnose problem4. Verify diagnosisPROVE YOUR POINT!Disable injector, EGR valve or O2 sensor, etc.Perform snap-test. Compare low & high RPM.Enrich fuel mixture, etc.
36at various speeds & loads. Disconnecting or disabling Dissecting andaccumulatinginformation.AnalysisExperimentingat various speeds & loads.Disconnecting or disablingto observe reaction.Conclusionbased onanalysis.DiagnosisVerify and qualify topinpoint malfunctionor component.
37Q.C. THE Q.C ANSWERS... If this is a representation of all cylinders superimposed, thereis 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.
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