6/30/2015 Point of No Return: Returnless Fuel Injection Systems

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PointofNoReturn:ReturnlessFuelInjectionSystems

Ifyouvetriedtofindthefuelpressureregulatoronmanylatemodelenginesbylookingintheenginecompartment,youwontfindittherebecausetheregulatorhasbeenrelocatedtothefueltank.Engineswithreturnlesselectronicfuelinjection(EFI)systemshavetheregulatorinsidethefueltank.Theregulatorispartofthefuelpumpassemblyandisusuallylocateddownstreamoftheintankfuelfilter.

Whyhavethevehiclemanufacturersgonetothistypeofsetup?Toreduceevaporative(EVAP)emissionsfromthefuelsystem.In2004,federalemissionregulationsrequiredlowerEVAPemissions.This,inturn,requiredachangetoreturnlessfuelinjectionsystemsonmanyvehicles.

Onaconventionalportfuelinjectionsystem,fuelisroutedtoafuelrailontheenginetosupplytheinjectors.Fuelpressureiscontrolledbyavacuumoperatedmechanicalregulatormountedonthefuelrail.Intakevacuumisroutedtotheregulatorthroughavacuumhoseandpullsagainstaspringloadeddiaphragmtomaintainapresetpressuredifferentialinthefuelsystem.Whenintakemanifoldvacuumishigh,excessfuelpressureisventedthroughtheregulatorbypassvalveandroutedbacktothefueltankviaafuelreturnline.Unfortunately,thiscarriesalotofengineheatbacktothefueltankandincreasesevaporativefuelvaporemissions.

Relocatingtheregulatortothefueltankeliminatesthecirculationoffuelbetweentheengineandtanksothefuelstayscooler.Italsosimplifiesthefuelsystemplumbingbyeliminatingthereturnline.Anotheradvantageisthatputtingtheregulatorinthefueltankkeepsitawayfromengineheatandextendsitslife.TheonlydownsidewiththereturnlessEFIsetupisservicingtheregulator.Iftheregulatorneedstobereplacedforanyreason,youhavetodropthefueltanktoextracttheintankfuelpumpmodule.Thesamegoesforthefuelfilter,whichisalsolocatedinsidethefueltankwiththepumpmoduleonmostapplications.

WhereYoullFindReturnlessEFIReturnlesssystemsarenowusedonmanylatemodelcarsandtrucks.Thefirstonesappearedbackin1993oncertainChryslerV6andV8truckengines.By1998,allChryslercarsandlighttruckshadthem.In1996,Toyotaintroduceditsfirstreturnlesssystem,andHondawentreturnlessin2001.GeneralMotorsandFordstarteddownthereturnlessroutein1999,andin2004,GMwentreturnlessonmostofitsfullsizepickuptrucksandSUVswiththeVortec6000(LQ4andLQ9)engines,includingtheCadillacEscaladeChevySilverado,SuburbanandTahoetheGMCSierraandYukonandHummerH2.

Actually,therearetwodifferenttypesofreturnlessEFIsystemsinuse:mechanicalandelectronic.Inthemechanicalsystems,amechanicalregulatorismountedonthefuelpumpmoduletoprovideamoreorlessconstantfuelpressuretotheengine.ThistypeofsetupworkswellwithaspeeddensityEFIsystemthatusesthrottleposition,intakemanifoldpressureandenginerpmtodetermineengineloadratherthananairflowsensor.

On1996ChryslerandDodgeminivanswithreturnlessEFI,theregulatorcanbeservicedbyremovingthefuelpumpmodulefromthefueltank,thenpryingbackthelockingtabsthatholdtheregulatorinitshousing.Theregulatorcanthenbepriedoutandreplacedwithanewone.TherearealsotwoO

6/30/2015 Point of No Return: Returnless Fuel Injection Systems

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ringsinsidethehousingthatalsoshouldbereplaced.Forgetthese,andthesystemmaynotholdnormalpressure.

ElectronicreturnlessEFIsystemsalsomaybereferredtoasOnDemandreturnlessEFIsystemsbecausetheyuseafueltankpressuresensortomonitorfuelpressure.ThePCMvariesthespeedofthefuelpumptoincreaseordecreasefuelflowusingpulsewidthmodulation(PWM)ofthepumpssupplyvoltage.ThePCMdetermineshowmuchfuelisrequiredbasedonengineloadandinputsfromitsothersensors.Thistypeofsystemistypicallyusedonanenginethathasanairflowsensortomonitorengineload.

2005ChevySilveradoOna2005ChevySilverado,forexample,theondemandreturnlessEFIsystemhasaturbinestylefuelpumpinsidethefueltankthatroutesfuelthroughanintankfiltertotheintankregulator.Theregulatormaintainsapresetpressuretothefuelinjectionsystem,whichis55to62psi(or48to54psionengineVINcodeZ).Afuelpressuresensorismountedontopofthefuelpumpmodulesopressureandflowcanbemodifiedasneeded.Thesystemhasanumberofdifferentoperatingmodes:

StartingMode:Whentheignitionisfirstturnedon,thePCMenergizesthefuelpumprelayfortwoseconds.Thisallowsthefuelpumptobuildpressureinthefuelsystem.ThePCMcalculatestheair/fuelratiobasedoninputsfromtheenginecoolanttemperature(ECT),massairflow(MAF),manifoldabsolutepressure(MAP)andthrottleposition(TPS)sensors.Thesystemstaysinstartingmodeuntiltheenginespeedreachesapredeterminedrpm.

ClearFloodMode:Iftheenginefloods,theenginecanbeclearedbypressingtheacceleratorpedaldowntothefloorandthencrankingtheengine.Whenthethrottlepositionsensorisatwideopenthrottle,thePCMreducesthefuelinjectorpulsewidthinordertoincreasetheair/fuelratio.ThePCMmaintainsthisinjectorrateaslongasthethrottlestayswideopenandenginespeedisbelowapredeterminedrpm.Ifthethrottleisnotheldwideopen,thePCMreturnstothenormalstartingmode.

RunMode:ThisincludesOpenLoopandClosedLoop.Whenacoldengineisfirststartedandisidling,thesystembeginsOpenLoopoperation.ThePCMignoresthesignalfromtheoxygensensorsandcalculatestheair/fuelratiobasedoninputsfromtheECT,MAF,MAPandTPSsensors.ThesystemstaysinOpenLoopfuelcontroluntilbothfrontoxygensensorsarehotandproducingavaryingvoltagesignal,enginecoolanttemperatureisaboveaspecified

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temperature,andacertainamountoftimehaselapsedafterstartingtheengine.

SpecificcalibrationvaluesfortheseconditionsarestoredinthePCMselectricallyerasableprogrammablereadonlymemory(EEPROM).Oncetheconditionsaremet,thesystemgoesintoClosedLoopandthePCMstartstocalculatetheair/fuelratioandmodifytheinjectorontimeusinginputsfromtheoxygensensorsandothersensors.

AccelerationMode:Whenthedriverpushesontheacceleratorpedal,theenginesucksinalotofair.Tokeeptheenginefromhesitating,thePCMincreasesthepulsewidthtotheinjectorstoprovideextrafuelenrichment.

DecelerationMode:Whenthedriverreleasestheacceleratorpedal,airflowintotheengineisreduced.ThePCMmonitorsthecorrespondingchangesintheTPS,MAPandMAFsensors.ThePCMshutsofffuelcompletelywhendeceleratingrapidly,andwhenthevehicleiscoastingdownwiththethrottleclosed.Thissavesfuelandpreventsdamagetothecatalyticconverters.

BatteryVoltageCorrectionMode:Ifbatteryvoltageislow,thePCMcompensatesfortheweaksparkdeliveredbytheignitionsystembyincreasingfueldelivery(enrichingtheair/fuelmixture),increasingengineidlespeedandignitiondwelltime.

FuelCutoffMode:ThePCMcutsofffuelfromthefuelinjectorswhenthefollowingconditionsaremetinordertoprotectthepowertrainfromdamageandimprovedriveability:Itdoesthiswhentheignitionisoff(preventsenginerunonwhentheengineishot)whentheignitionisonbutthereisnoignitionreferencesignal(preventsfloodingorbackfiring)whentheenginespeedistoohigh(revlimiter)whenthevehiclespeedistoohigh(speedlimiter)andduringanextended,highspeed,closedthrottlecoastdown(reducesdecelemissionsandincreasesenginebraking).

DiagnosisReturnlessEFIsystemsaresubjecttothesameproblemsasanyothertypeoffuelinjectionsystem:pumpandrelayproblems,pluggedfuelfilters,dirtyinjectors,evenbadgas.Consequently,diagnosis

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issimilar.

ReturnlessEFIsystemstypicallyoperateatahigherpressurethanreturntypesystems.Thisisnecessarytoreducetheriskoffuelboilingandvaporlockintheinjectorsupplyrailduringhotweather(sincethereisnorecirculationoffuelfromtheenginebacktothetanktokeepthefuelsupplyrailcool).Becauseofthis,areturnlessEFIsystemmaynotperformwelliffuelpressureorflowislessthanspecifications.

Fuelpressurechecksonreturnlesssystemscanbedoneintheusualwaybyattachingagaugetotheservicevalvefittingonthefuelsupplyrail,oryoucanhookupascantoolandlookatthefuelpressurePIDtomeasurefuelpressure.Youcanalsouseafuelpressuregaugetocrosschecktheaccuracyofthescantoolfuelpressurereading(whichwilltellyouifthefuelpressuresensorisoutofcalibration).

Onreturnlesssystemsthatusepulsewidthmodulationtovarythespeedofthefuelpump,youshouldbeabletoreadthevalueofthecontrolsignalonyourscantool.Lookforachangeinthenumberwhenenginespeed/loadchanges.Nochangewouldtellyoutheresaproblemwiththefuelpressuresensor,orpossiblythefuelpumpdrivercircuitinthePCM.

Fuelvolumeshouldalsobemeasuredifyoususpectaweakpumpisstarvingtheengineforfuelathigherspeedsandloads.Aweakpumpcanoftengenerateenoughpressureatidletomeetspecifications,butrunsshortwhenthedemandforfuelgoesup.Asarule,agoodpumpwilldeliveratleast750ml(3/4quart)offuelin30seconds.

ServiceLowfuelpressureand/orflowcanalsobecausedbyapluggedfilter,byrestrictionsinthefuelline,orlowvoltagetothepumpitself.ThefiltersonmostreturnlessEFIapplicationsarelifetimefilterswithnoscheduledreplacementinterval.Undernormalconditions,mostshouldlastupwardsof100,000miles,buttheywontlastthatlongifthevehiclehasrustordirtinthegastank.Replacingthefilterrequiresdroppingthetank,removingthemoduleand,inmostcases,replacingtheentirefuelpumpmodulebecausethefiltercannotbereplacedseparately.Imaginetellingyourcustomerheneedsanewfuelfilteranditwillcost$600tochangeit!

Ifanintankfilterhasbecomeclogged,orthefuelpumphasquit,besuretoinspecttheinsideofthefueltankafteryoupulloutthefuelpumpmodule.Dirtandsedimentcanberemovedbysteamcleaningthetank.Butifametaltankisrusty,replacethetanktopreventarepeatfailureofthenewpumpmodule.

SomethingelsetowatchoutforonreturnlessEFIsystemsiscontaminantsinthefuelrailontheengine.Therailisadeadendasfarasfuelcirculationisconcerned.Fuelflowsonewayintotherailanddoesnotreturntothetank,soanyjunkthatgetspastthefuelfilterwillendupintherailorinjectors.Theinjector(s)attheendofthefuelrail(s)furthestfromtheinletaretheonesmostlikelytobecomecloggedwithgunk.

Injectorscanbecleanedwithfueltankadditivesoroncarflushingequipment.Buttherailshouldberemovedandcleanedseparatelyifoneormoreinjectorsarefoundtobeclogged,ortheinjectorsarebeingcleanedoffcarorarebeingreplaced.

Gasolinethatdoesnotcontainadequatelevelsofdetergentcanallowfuelvarnishdepositstobuildupintheinjectors,restrictingfueldeliveryandcausingleanmisfireproblems.Depositscanalsoformontheintakevalves,pistontopsandcombustionchamberthatadverselyaffectperformanceandcompression.MostvehiclemanufacturersnowrecommendusingTopTiergasolinesthatcontainhigherlevelsoffuelsystemcleaningadditivestokeeptheinjectorscleanandtopreventengine

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depositbuildup.Thealternativeistousesometypeoffuelsystemcleaneradditiveinthefueltankperiodically(sayevery3,000to5,000miles),ortorecommendaperiodicfuelinjectorandenginecleaning.ThelattercanoftenrestorenormalperformanceandmakeanoticeableimprovementinfueleconomywhetheranenginehasreturnlessEFIsystemornot.

DidYouKnowIntheolderreturntypesystems,thefuelpumpdeliversmorefueltotheenginethanitactuallyneeds.Theexcessfuelisthenroutedbacktothefueltankthroughapressureregulatorandreturnline.Butinareturnlesssystem,thereisnopressureregulatoronthefuelsupplyrailandnoreturnlinebacktothetank.Theregulatorismountedinthefueltankandisusuallypartofthefuelpumpmodule.