essential scope techniques - macsw.org

PeterF.Meiertechnicaleditor,MotorAgeMagazine

08Fall

EssentialScopeTechniques

[ C o m p a n y A d d r e s s ]

EngineMechanical:RelativeCompressionUsingStarterDraw

Performingatraditionalcompressiontestcanbetimeconsuming,andcostlytothecustomer.Usingtechniqueslikethisonecan,ataminimum,identifyweakperformingcylindersandjustifytheneedformorelaborintensivetesting.Besuretodisablethefuelsystemtopreventfuelfromwashingdownthecylinderwalls.Patternnotes:

• Lookforpeaksthatarelowerthantheothers.Mostmodernscopescandetectaslittleasa10%lossbetweencylinders.

• Triggeringoffofanignitionsource(primaryorsecondary)allowsyoutodotwothings.One,youcanusefiringordertodeterminewhichcylinderanylowpeaksareassociatewithandtwo,youcanchecktimingbylookingforthefiringlinetopassnearthecenterofitsassociatedpeak.

• Ifvalvetimingisoff,thepatternwilllooknormalbuttheamplitudeoftheindividualpeakswillbeless.Valvetiminglowerscompressionequallyacrossallcylindersthatsharetheoutoftimecam.Keepthatinmindwhendealingwithmultiplecamengines!

EngineMechanical:Relativecompression(knownbad)

Additionalnotes

EngineMechanical:Relativecompressionatexhaust

Rememberthe“dollarbill”trickfortestinganenginewithasuspectexhaustvalve?Thedollarbillwouldbesuckedintothetailpipeeverytimethatcylinderhititsexhauststroke.TheFirstLookpressuresensorallowstheuserto“see”thosepressurepulsesastheyhappen.Patternnotes:

• Thenumberofcylindersandexhaustlayoutwillaffecttheactualshapeofthispattern.Don’tfocusontheminorvariations.Insteadlookforthe“oddmanout”.Focusontheforest,notthetrees!

• Identificationoftheweakcylindercanstillbedonewiththeignitiontrigger,butyouhavetoadjustforthetiming.Remember,you’relookingattheexhauststroke,notthecompressionstroke,onthiswaveform.

Additionalnotes:

CheckingcrankcasepressuretoisolatecompressionlossOnegreatadvantageofusingapressuresensorinsteadoftraditionaltestingisthespeedatwhichyoucanquicklyisolatethecauseoftheproblem.Ifyourstartercurrenttestortailpipetestindicatesaweakcylinder,movethesensortotheoildipsticktubeandrunthetestagain.Patternnotes:

• Thistestmeasurescrankcasepressurefluctuation.Asthepistonsmoveupanddown,theycreatechangesinpressure.Ifapiston’sringsarenotsealing,itwillshowuphere.Astablepatternindicatesthelossofcompressionhastobecomingfromthetopend!

Enginemechanical:Intakemanifoldvacuumwithapressuretransducer

Bothpressuresensorsandpressuretransducerscanbeusedtotestintakemanifoldvacuum.Transducersmeasuretheactualpressurerelativetozero,whilesensorsreacttopressurechangeonly.Lookatthefluctuationsbycylinderandrememberwhatstrokeyou’reon!Thisone,usinganinjectorasareference,canmakedeterminingthecylinderyou’relookingforalittlemorechallenging.Next,imaginewhatatraditionalmanifoldvacuumgaugewouldbedoingasthesepressurechangeswereoccurring.(I’veincludedareferenceforyouruseinthishandout).Isthisagoodpattern?Whyorwhynot?Whatdoesthepressurereadingequateto?Why?

Whichiscorrect?(Triggeron#2injector,firingorder1-5-3-6-2-4)

Additionalnotes:

Enginemechanical:In-cylindercrankingcompression

Theuseofanin-cylinderpressuretransducerhaslotsofuses.Ittakesjustasmuchtimeastheuseofatraditional,mechanicalcompressiongaugebutitallowsyoutoseesomuchmore.Insteadofsimplyreadingapeakpressure,youcanobservethepressurechangesintheengineovertheentire720̊ofthefour-strokecycle.Patternnotes:

• Crankingcompressionpressureslessthan90psiisinsufficienttosupportcombustion.

• Formostengines,alinedrawnthroughthepeakwillsplitthepatternintosymmetricalhalves.Ifnot,andthepatternisaccompaniedbyadeeperthannormalexhaustpocket,thereisaleak.

Therearesoftwareapplicationsthatcanmakerotationaldegreehighlightingquickandeasy.Ifyoudon’thaveone,youcanuseWindow’s“Paint”programtomarkthemoffyourself.Simplypastethescreencaptureinto“Paint”andplaceyourmarkingcursoratthetopofonepeak,andthentheother.Atthebottomofthe“Paint”window,you’llseeapixelcoordinatelike100,210.Thefirstnumberisthehorizontalelementandthesecondistheverticalelement.Notethefirstnumber,andthenmoveyourcursortothesecondpeak.Subtractthefirstfromthesecondandyou’llgetatotalpixelspreadforyourcapture.Dividebyfourtodividethespaceinto180̊segments,byeightfor90̊,andsoon.

UsingWindows“Paint”notes:Knownbadexample

Additionalnotes:

EngineMechanical:In-cylinderrunningpressuretest

Therunningin-cylinderpressuretestisavaluablediagnostictool.Notonlycanyouidentifycylindersealingissuesandcauses,youcanusethismethodtotesttheoperationofvariablevalvetiming,verifycamandignitiontiming,andcatchintermittentlysealingvalvesintheact.Patternnotes:(Usethissectiontowritedownwhatcaughtyourattentionaboutthisdynamictestingmethod)Tolearnmore,readtheseriesonIn-CylinderPressureTestingauthoredbythemanwhodevelopedthetechnique,BernieThompson.YoucanaccessallofBernie'sarticlesonMotorAgeat:https://www.searchautoparts.com/motorage/author/bernie-thompson

In-cylinderrunningpressurepatternelements

A:TDCofthecompressionstroke TDClinetypicallysplitspeakintosymmetricalhalves.B:BDCofthepowerstroke ExhaustvalveopensjustbeforeBDC.LookforBDCtointersectrampinareamarkedby“G”.C:TDCoftheexhauststroke Theplateaubetween“B”and“C”ispressureintheexhaustmanifold.H:Theintakevalveopenswhiletheexhaustisstillopen(overlap).Pressuredropisresultofexhaustclosingandcylinderexposedtointakemanifoldabsolutepressure.Lookforramptointersectinareamarkedby“H”.D:BDCoftheintakestroke. Thispressureshouldbenearidenticaltothatintheexhaustpocket.Noteline“F”.E:BacktobeginningofpatternatTDCcompression.

Additionalnotesonin-cylinderrunningpressurepattern:

Additionalnotes:

Enginemechanical:Cam/cranksensors

Comparingknowngoodsynchrelationshipstotheonescapturedonaproblemcarisanotherwaytocheckcamtiming.Findingtheknowngoodpatternsiseasierthanever,withresourcesavailablefromsiteslikeiATN,Wavehook.com,Autonerdz,andothers.Butthatisn’ttheonlyvalueinthesecaptures.Tieininjectorand/orignitioneventstoseeifthereareanyproblemswithECMcontroloftiming.Usethezoomfeaturestocheckthecircuitsforvoltagedropjustasyouwoulduseyourvoltmeter.Patternnotes:

Knownbad

Created

Fuelsystemtesting

Manypressuretransducersallowyoutomonitorfluidpressuresaswellasairpressure.Thisopensupallnewdoorsfortroubleshootingsystemslikefueldelivery.Theuseoffuelpumpcurrentpatternsasatroubleshootingtoolisanexampleofhowinventivetechscreatediagnosticstrategiesandthensharethemwithothers.Nowitisconsideredastandarddrivabilitytroubleshootingtechnique.Let’smakesureyoucantakefulladvantageofthemboth.Patternnotes:

• Currentpatternscantellatechalotabouttheelectricalandmechanicalhealthofthefuelpump.Eachpeakisthecurrentreadingofonesetofcommutators,onewindinginthepumpmotor,asitpassesthroughthebrushes.Low,deformedpeaksindicatebrushandcommutatorwear.

• Currentcanalsotellusthespeedofthepump.Thisknowledge,whenbackedbycurrentdraw,canpointatechinthedirectionofrestrictedfuelflow(cloggedfilters)orevenemptygastanks!

• Pressuresensorscanallowatechtoperformaninjectordroptestinminutes,withouttheneedforascantool,manualinjectordriver,ortraditionalfuelpressuregauge.

• Pressuretransducerscandothesame,butwiththeaddedadvantageofprovidinganaccuratepressuremeasurementandmonitoringofthatpressureoveranytimebaseourscopeiscapableof.

Fuelsystemtesting:Fuelpumpcurrent

Fuelpumpcurrentpatterncantellyouabouttheelectricalandmechanicalhealthofthefuelpump,andtheabilityoffueltomovethroughthesystem.Highpumpspeedandlowcurrentdrawcanindicate:Lowpumpspeedandhighcurrentdrawcanindicate:Normalpumpspeedandlowcurrentdrawcanindicate:

Additionalnotes:

Fuelsystemtesting:Fuelpressurewithtransducer

Usingapressuretransducerinplaceofatraditionalpressuregaugewillnotonlyallowyoutomeasurepressure,butseethepressuredropacrosstheinjectors.

Fuelsystemtesting:Fuelpressureusingapressuresensor

TheFirstLooksensorusedhereisjustlikeitstailpipecousin.Itreactstopressurechange,butdoesnotmeasureactualpressureinthesystem.

Additionalnotes:

Fuelsystemtesting:Fuelinjectorvoltageandcurrent

Injectorpatternscanhelplocatestickinginjectors,ornaildownintermittentissues.CAUTION:Besuretoknowtheinputvoltagelimitsofyourscope.Injectorkickbackcanexceedthecapacityofmostscopes,requiringsomeformofattenuation.Markwheretheinjectorpintleopensinthiscapture.Markwheretheinjectorpintleclosesinthiscapture.Wherewouldyoumeasurecommandedontime?Actualopentime?

Whatiswrongwiththiscapture?

Whataboutthisone?

Howcouldyoucatchanintermittentproblemusinginjectorcurrent?

Isthecalculationofresistanceaccurate?Whatothersystem(s)doyouthinkyoucanapplythisto?

Ignitionsystem:Secondaryignitionpatterns

Isthisanormalpattern?Firingvoltageisaffectedby:Sparkvoltageisaffectedby:Whydoesthesecondcurrentrampnotstartat“0”amps?

Sparkdurationisaffectedby:HighsparkkVwithanupwardslopingburnlinecanindicate:LowsparkkVwithadownwardslopingburnlinecanindicate:Aburnlinethatdisplayspeaksandvalleysmayindicate:MasterignitionwaveformanalysiswiththehelpofJimMorton'svideo!https://youtu.be/yCchGNQEMdE

Additionalnotes:

Ignitionsystem:Primaryignitionpattern

Modernignitionsystemscanmakecapturingasecondaryignitioneventdifficult.Theprimaryignitionpatternmaybethealternativeyouneedtocapturethewaveform.CAUTION:Primaryvoltagecanexceedthemaximuminputvoltagecapabilityofmostscopes.Capturingthispatternmayrequiretheuseofsomeformofattenuation.Whatisthesameaboutthispatternwhencomparedtothesecondary?Whatisdifferent?Canthispatternbecapturedonallvehicles?

Currentcutoff

Samplerateexample

78,130samplespersecond(oneevery12.8microseconds)allowyoutozoominwithdetail.Verticalresolutionmakescurrentslopesmoreaccurate.

Battery-starting-chargingsystemtesting

Howwouldyouliketobeabletoperformacompletesystemtestinlessthan5minutes?Knownbad

Battery-starting-chargingsystem:Batteryvoltage

Opencircuitvoltageis:In-rushvoltageis:Loadedvoltageis:Chargingvoltageis:

Battery-starting-chargingsystem:Startercurrent

Howisthistriggerset?Whatisthepeakvoltage?Whyisitsohigh?Canyouidentifyonthepatternwheretheenginestartedrunningonitsown?Whatdothetwopeaksthatoccuraftertheinitialspikemean?Whatisconsideredanacceptablecurrentreadingafterthevehiclehasbeenrunningfor3-5minutes?Whatdoesahigherthannormalreadingindicate?

Additionalnotes:

Backtothebadpattern

Thisiscausedby:Knowngood:

Resources:AES http://www.AESWave.comAutomotiveTestSolutions http://www.AutomotiveTestSolutions.comAutonerdz http://www.Autonerdz.comInternationalAutomotiveTechniciansNetwork(iATN) http://www.iATN.netPico(UK) http://www.PicoAuto.comDiagnosticNetwork http://www.diag.net/