Da pneumatic/hydraulic modulator is used torelease fuel back to the tank. The regulator’sreturn flow corresponds inversely to pressurein the intake manifold. As manifold pressureincreases (increased load), the regulator returnsless fuel back to the tank. As manifold pressuredecreases (reduced load), the regulator returnsmore. On most cars, the electric fuel pumpworks at 100 percent capacity the entire timethe engine is running, but the engine rarely ornever uses all the fuel pumped.

At low coolant temperature, wide-open throttle,high load and high rpm, the engine burnsalmost all the gasoline the pump delivers. At high coolant temperature, idle and no load,the regulator returns most of the fuel back to the tank. This way the difference between thepressure of the fuel in the rail and the pressureof the air in the intake manifold remains constant.With a constant pressure difference, the onlyvariable determining the quantity of fuelinjected is the pulsewidth. This is the timethe computer turns the injector on.

As fuel re-enters the tank, it produces substantialvapor. With tighter emissions standards, laterinjection systems have no pressure regulator or return line and run at a constant fuelpressure. It turned out easier to control fuelmixture at a constant fuel pressure (regardlessof manifold vacuum/pressure) rather than toexpand and complicate the charcoal canistervapor purge system. Fuel injectors on these‘returnless’ fuel injection systems work thesame as on the previous systems, but withshorter pulsewidths at low manifold pressure.When there is a greater difference between thefuel and the intake air pressure – at idle anddeceleration – injector pulsewidth is extremelybrief, or even non-existent.

FUEL RAMPING, CURRENT RAMPINGFuel volume corresponds closely to the injectors’pulsewidth, but not in a linear correspondence.Understanding the electricity and fuel hydraulics

For many years, almost every new car and truckin the United States has delivered its fuelthrough fuel injectors, usually one to a cylinder.The description fuel injector is misleading:Just as shock absorbers don’t absorb shocks(the springs do), fuel injectors don’t inject fuel(the fuel pump does). Most of the time, injectorssimply block the flow of fuel. Only when thecomputer activates them by completing theirelectrical circuit, do they open and let fuelspray. Fuel injectors are fast-acting, preciseelectromechanical nozzles, metering thepressurized fuel into a finely atomized sprayfor the next power stroke.

SPOOLS AND NOZZLESIn the hundred and fifteen years since the firstfunctional automobile [Patentwagen 1886,Karl Benz Entwickler, Untertuerkheim – JW],there have been many types of fuel injectors,but the majority now work when anelectromagnetic coil lifts a ferrous pintle or

needle off its seat so fuel can squeezethrough the nozzle’s aperture and into the intake air channel. Becausegasoline has such low viscosity, even

minuscule pintle movement is enough torelease the amount of fuel the engine needs

WHAT’S INSIDE: Fuel Injectors…Page 1& 3 / FINE TUNING…Page 2 / QUALITY POINTS: Wells Adds State-of-the-Art Component Placement Systems…Page 2 HOT OFF THE WIRE: Wells 2001 Catalog & Parts Guide Now Available, Publisher’s Information…Page 4

CounterCounter PointT H E E L E C T R O N I C, D I A G N O S T I C A N D D R I V E A B I L I T Y R E S O U R C E.

Volume 5 Issue 1, January 2001

continued on page 3

Fuel Injectors…To Begin With

next. The Powertrain Control Module (PCM)operates the fuel injectors, varying their deliveryvolume by the time it actuates their coils, theon-time or pulsewidth is measured in milliseconds.The computer calculates this time based oninformation from its sensors.

These include the throttle position sensor, theengine coolant temperature sensor, the intakemanifold pressure sensor, the cam- or crankshaftposition sensor and various other inputsdepending on the vehicle’s fuel/ignition system.

Most fuel injection systems determine fuelpressure at the injectors by the interworkingof the fuel pump and the fuel pressure regulator,

eliver exactly the

right amount

of fuel for one

cylinder – that’s the task for

each fuel injector. Here’s how

it does the job, and how to

tell when it doesn’t.

ElectricalConnector

Coil Windings

Pintle

Nozzle

Q: “I recently replaced the distributor cap,rotor, and spark plug wires in my 1993Jeep Grand Cherokee, 6-cylinder, with Wellsproducts. Since that time, my garage dooropener will only work about 50% of thetime when the vehicle is running. If I turnoff the ignition, the opener works 100% ofthe time. I tried a newer door transmitterfrom the manufacturer, but it has the sameresult. Have you ever had this problembefore? Do you have any suggestions?”

Mark Hull, Wausau, WI

The problem you are experiencing can be avery difficult one to pin down. It is caused byradio frequency interference (RFI). RFI occurswhen electricity bridges a gap. Check the sparkplug connections, you will feel a “snap” whenthey are correctly installed. Make sure you arenot running the ignition wires completelyparallel to each other. The spark plugs needto be the resistor type. Because of the differencein the porcelain from various manufacturersbe sure to use the die-electric grease providedwith the wire set.Results: installing the die-electric greasesolved the problem.

Q: “I have a 1991 Ford Explorer with 100,000miles on it. I have owned it since it wasnew. Recently I have been experiencing apinging noise when I am driving down thehighway at cruising speed. If I accelerate,the ping goes away. I talked to my localgarage and the technician there says Ishould disconnect the Octane clip. Does

this sound correct to you or can you giveme another idea?”

Wayne Smits, Depere, WI

In the technical services department we havereceived several calls pertaining to the problemyou are experiencing. We have found that themass airflow (MAF) sensor is usually at fault.On your vehicle the MAF sensor functions bykeeping a coiled wire at a constant temperature.The current flow necessary to keep the wiretemperature constant determines the amountof mass air entering the air intake. This coiledwire will become contaminated over time. Withthis contamination on the wire the PCMcalculates less air than what is actually enteringthe intake. In turn the PCM will lean the fuelmixture. With a lean mixture a ping is created.I would suggest a close inspection of the MAFwires. If one is contaminated with grit the MAFneeds to be replaced or cleaned.Results: after the MAF was replaced, theproblem was resolved.

I have a ’96 Mercury Grand Marquis with a4.6L engine. The Malfunction IndicatorLamp(MIL) has been coming on. Ichecked the codes and a P0121 was stored in the PCM. This code means thecalculation between the MAF and TPSare not within specs. I have replaced both theTPS and MAF sensors and the light still comeson. What could be wrong?

The first reader to respond with the most accurateanswer via e-mail or fax, and the first reader torespond with the most accurate answer viasnail-mail, will each receive a Wells golf shirt.The answer, and the winners’ names, willappear in the next issue.

Here is the answer to last issue’s questionregarding the 1997 Ford Taurus 3.0L withthe random misfire codes:

At first it may seem like everythingimaginable has been checked, reprogrammedor replaced to repair the intermittentmiss fire on this 1997 Ford Taurus. Theinjector’s feed wires have been thoroughlytested. However, the ground side is what reallycontrols the function of the injector. If thePCM has an intermittent driver(s) to the injector(s)it would cause this problem. Another reasonfor this problem would be Electromagneticpulses (EMP’s). For example if the ignition wiresare routed too close to the primary wires theycould induce random false signals to the PCM.

The first correct answer we received was fromTony Greco from Comack, NY.

volumes or placement rates. Wells upgraded theircurrent DIS assembly line with the latest technologyavailable in pick and place equipment. It has theflexibility to pick components not only frommagazine feeders but also from multi-stick feedersas well. The placement heads alternately pick upcomponents from the stationary componentfeeder and place components on the substrate,which is motionless. This allows for extremelyaccurate placement.

With current demands and increasing additions of new sensor assemblies, Wells also upgraded

the current sensor assembly line surface mountequipment with a high-speed flexible machinerated at 18,000 components per hour. Eightplacement heads simultaneously pick componentsfrom any mix of feeders and scan on the flyacross a vision camera ensuring accurateplacement of all components.

At Wells, our investment in new technologyis driven by our commitment to you. Wewant to ensure that no matter what productwe supply you; it is manufactured to thehighest quality standards and delivered on a timely basis.

2

Quality

FineFine Tuning

Quality PointsWells continues to grow and add new products.In order to meet those growing needs in aneffective and efficient manner, we continuallyinvest in new equipment and upgrades.Recently, we upgraded our Surface MountTechnology (SMT) equipment to allow foradditional placement capacity.

SMT component placement systems are rapidlyevolving with particular focus on two distinctsystem features. The first relates to the capability of handling the next generation of surface mountcomponents and second is to handle increased

Wells Adds State-of-the-Art Component Placement Systems

Diagnose The Problem Win A ShirtDiagnose The Problem Win A ShirtFine Tuning questions are answered byMark Hicks, Technical Services Manager. Please send your questions to: Mark Hicksc⁄ o Wells Manufacturing Corp.,P.O. Box 70, Fond du Lac, WI 54936-0070 or e-mail him attechnical@wellsmfgcorp.com. We’ll send you a Wells shirt if yourquestion is published. So please includeyour shirt size with your question.

Contaminated MAF Sensor

involved accounts for how an injectorcan deliver a wide range of volumeover a relatively small range of injectoron-time. If you watch fuel spray from

an injector, it seems to blast on instantly atfull force and then to snap off. This is a trickof the eye. We cannot see different eventsseparated by less than approximately a twentiethof a second from one another. The fuel flowactually ‘ramps’ gradually up and graduallydown, though over a very short, millisecondof time. The flow rate at any instant is theproduct of the exact position of the pintle.We’ll see shortly how this allows the wide rangeof delivery volume and, even more important,what this means when there are mechanical orelectrical problems with an injector.

It’s not only fuel flow that ‘ramps’ upand down at the beginning and end of

an injector pulse. The electric current throughthe injector’s coil behaves similarly because ofthe coil’s reluctance. Reluctance is a form ofelectrical resistance unique to coils. As electriccurrent flows through the coil’s windings, itbuilds a magnetic field pulling the pintle offits seat and releasing the fuel. But as that fieldgrows, its lines of magnetic force pass throughthe same windings, causing a reversed-polarityvoltage resisting the applied current. Finally,the reluctance disappears just as the coilreaches full magnetic saturation, the lines ofmagnetic force become stationary and theapplied current reaches its maximum potential.When the PCM cuts the injector coil circuit,the magnetic field collapses. But as it collapsesthose same magnetic lines of force pass throughthe coil windings in the opposite direction,thus extending the duration of the magneticfield and the opening of the nozzle.

This answers a puzzle. You know the vehicle’ssystem voltage, and you can measure the coil’s

room-temperature resistance. UsingOhm’s Law, it ought to be possible to calculate the current through aninjector coil. Of course, the injector

is not constantly activated, so you’d multiplyyour calculated product by the duty-cycle (the percentage of time-on to time-off ). But

3

continued from page 1

Fuel Injectors...To Begin Withyou get an amp number substantially higherthan you’ll measure with an ammeter. Why?Because of the reluctance, the current flowingthrough the coil functions as an electromagneticbrake on itself until the coil is saturated. If youmonitor this current with an oscilloscope, theshape and slope of this current ramp reveal a great deal about the condition of the injector,as we’ll discuss in subsequent articles. Forpresent purposes, though, the current is whatmatters: Electromagnetism, the force thatmoves the pintle, is directly proportional tocurrent. This verifies the pintle movement is also gradual.

Since the PCM controls the injector’s on- andoff-time, it can achieve very small but veryprecise pintle movement and correspondinglysmall but precise doses of fuel with a very shortinjector pulsewidth, hardly lifting the pintleoff the seat. When conditions call for it, thePCM can achieve a large-volume delivery byextending the injector’s pulsewidth, maximizingthe time the injector flows as much fuel as itcan. The difference in fuel per power stroke anengine requires varies by more than 100 to 1from cold maximum power to warm idle, butthe available pulsewidth of the injectors variesby much less. High volume injection is simpleto achieve with maximum pump capacity andenough injector flow-through. It’s at low volumethat injector problems become most apparent.Only by using the fuel flow delay resulting fromcoil inductance, pintle and fuel inertia can thePCM deliver the smallest fuel quantities requiredwith the accuracy to meet emissions standards.

PLUGS AND SHORTSInjector problems fall into two groups: mechanicaland electrical. Bad fuel and water in the fuelhave damaged many injector nozzles and/orpintle tips. You can identify mechanical problemsby a visual inspection of the fuel spray pattern.Listening for an injector’s click (or its absence)can point to the first injector to observe. If gritor contaminated fuel get past the main filter,they’ll quickly plug the small mesh filter in thetop of the injector. Deposits formed from fueldroplets that evaporate after an engine shutsoff can form gums and tars that clog an injectoror skew its spray pattern, preventing the fuelfrom vaporizing completely. Sometimes suchdeposits prevent the pintle from seatingcompletely, so the injector dribbles fuel. Whilefuel cushions the injector pintle’s closing againstthe seat, it’s still a mechanical part and willeventually show wear and begin to leak. Eventhe slowest unmetered leak can often transmitmore fuel than we want at unloaded warmidle, as we saw above.

Most failed electrical circuits first become ashort circuit and then quickly burn open, butwith fuel injectors, you often notice driveability

problems before the injector shorts completely.An injector that loses electrical resistance canhave an interesting and puzzling effect. Theusual way a coil changes resistance is by meltingthe thin insulation between adjacent windingsof the wire. The failure does not occur all of a sudden. If the coil has 100 loops of wire, ashort across the insulation between two loopscan reduce the coil’s resistance by no morethan one percent, even if all the current wentthrough the partial short circuit. Such a shortmay not noticeably affect the injector. It couldbe very hard to detect with even the bestohmmeter since new injector’s resistance varymore than that and temperature changesaccount for even more. As the resistance goesdown, the current goes up, as current goes upso does the heat. The heat increase will meltthe next most vulnerable insulation barrieruntil it also forms a short.

Before long, that partially shorted injector pullsnoticeably more current than the others. It israre for an injector to burn all the way shortedor open. On most vehicles the PCM will shutthe injector off to protect the driver transistorswhen the current exceeds or falls below a certainthreshold. Some cars shut off all the injectorsif any are shorted or open.

But before that happens, you may find thefollowing: Often two injectors or even entirebanks of cylinders fire together, particularly on earlier fuel injection systems and on engineswith waste-spark ignition. The injector withlower resistance draws more current becauseelectricity always follows the path of leastresistance. Increased current to the partiallyshorted injector may ‘starve’ the paired injectorof current so it can’t lift its pintle and its cylindergets little or no fuel. We then have the oddcircumstance that the good injector does notspray enough for combustion but the defectiveone keeps working – not for long, but longenough to leave a diagnostician puzzled.

Usually fuel injectors operate and spray oncefor each complete engine cycle. Some vehiclesuse additional squirts for cold starting, accelerationenrichment or for other special conditions.Some vehicles have more than one set of injectors(and more than one set of intake runners) foreach cylinder, employing the second set onlyunder conditions of very high power demandand high engine speed. But the way individualinjectors work in these systems is the same asin everyday vehicles.

In the next Counterpoint, we’ll look at particulartypes of injectors and their characteristic problemsand the tests for those problems.

Fuel volume will intensify as the injector’sCurrent flow increases.

Wells Manufacturing Corp.has published its extensive2001 Engine ManagementSystems Catalog and 2001Illustrated Parts Guide,which incorporate more than3,000 new part numberscovering through model year2001 vehicle applications.

The 2,291-page catalog hasbeen divided into two volumesfor easier storage and use. Volume 1 coversAcura through Ford passenger cars, whileVolume 2 covers Ford trucks through Yugo.Both volumes also feature Professional GoldProgram listings.

The fully-illustrated parts guide contains1,014 pages of detailed information andseveral new categories, including:

WELLS MANUFACTURING CORP.P.O. Box 70Fond du Lac, WI 54936-0070

Hot off theHot off the WireWells 2001 Catalog & Parts Guide Now Available

INSIDE:Fuel Injectors

• Four Wheel Drive Indicator Switches

• Four Wheel Drive Selector Switches

• Power Seat Heater Switches• Rear Window Release Switches

In addition to these features, an alpha locator program hasbeen implemented. The locatorprogram indicates the size of eachproduct box with an alpha code.

This allows for improved utilization of shelfspace, which maximizes return on investmentthrough better inventory management. The program enables all like-size boxes to be plan-o-grammed together.

For information on obtaining copies of thepublications, contact your nearest Wellsdistributor or representative.

Publisher’s Information

Wells’ President ..............William AllenVice President of Sales ....Gavin SpenceTechnical Services Manager .. Mark HicksNewsletter Editor .........Danny SciortinoCounter Point is a quarterly publication of WellsManufacturing Corp., P.O. Box 70, Fond du Lac, WI54936-0070. Letters and comments should bedirected to: Counter Point Editor, c/o Wells Manufacturing Corp., P.O. Box 70,Fond du Lac, WI 54936-0070.© COPYRIGHT 2001 WELLS MANUFACTURING CORP.All rights reserved. No reproduction in whole or part is permittedwithout the written consent of Wells Manufacturing Corp.