Counterounter Point

1 WHAT S INSIDE:WHAT S INSIDE: making Sense of Oxygen 1 / Counter Point Celebrates Its First 1 / FINE 2 /QUALITY points : WELLS Premium Spark Plug Wire 3 / HOT OFF THE WIRE: Isolation Diagnostic 4 / Publisher s 4 making Sense OfOxygen SensorsCounterCounterPointTHE ELECTRONIC, DIAGNOSTIC AND DRIVEABILITY 2 Issue 3, September 1998 Volume 2 Issue 3, September 1998 Today s computerized engine control systems rely on input from a variety of sensors to regulate engine performance, emissions and other important O2 sensor failure or a problem in the sensor swiring circuit will prevent the system from going intoclosed loop causing a rich-fuel condition, increasedemissions (particularly carbon monoxide) and fuelconsumption. Keep in mind that a bad coolanttemperature sensor can also prevent the system fromgoing into closed THE O2 SENSOR WORKSThe O2 sensor used in most vehicles is a voltagegenerating sensor.

2 The tip of the sensor has azirconium ceramic bulb coated on the inside andoutside with porous platinum, which serve as theelectrodes. Inside the bulb are two platinumelectrodes. The inside of the bulb is vented throughthe sensor housing to the outside the bulb is exposed to hot exhaust, thedifference in oxygen levels across the bulb creates avoltage. The sensor will generate up to about voltswhen the fuel mixture is rich. When the mixture islean, the sensor s output voltage can drop as low as volts. When the air/fuel mixture isbalanced (about :1), the sensor will generatearound sensors must provide accurate informationotherwise driveability problems, increased fuelconsumption and emission failures can of the key sensors in this system is the oxygen(O2) sensor.

3 The O2 sensor is mounted in theexhaust manifold to monitor unburned oxygen inthe exhaust. The O2 sensor tells the computer if thefuel mixture is burning rich (less oxygen) or lean(more oxygen). The computer then uses the sensor svoltage signal to alter the fuel mixture, creating afeedback loop that constantly rebalances the the engine is first started, the computer is in open loop and does not use the signal from the O2sensor. The fuel mixture is set to run rich and staysthat way until the system goes into closed loop andstarts using the O2 sensor signal to vary the fuel mixture. Most late-model O2 sensors are heated so they will warm up and reachoperating temperature sooner to reduce O2 sensors typically have three or four wires. Older single-wire O2 sensors do not have PointCommemoratesIts First Year!

4 With this issue, WELLS Counter Pointnewslettermarks the conclusion of its well-received first yearof publication, a year in which more than 20,000subscription requests were received. The favorable response from technicians andothers involved in automotive repair has been evenmore than we expected, said Gavin Spence, VicePresident of Sales for WELLS Manufacturing Corp. Our goal from the start has been to make Counter Pointa valuable automotive diagnosticresource, presented in a straightforward, easy-to-read style. We re pleased that so many technicianshave told us we achieved that. We ll work to makeCounter Point even more useful in the future. Despite the tremendous response already,we will continue to honor subscription mail them to WELLS, Box 70, Fond du Lac,WI 54936-0070.

5 We also welcome your commentsand technical quick note: we ve changed the publicationdate for this issue from August to September, toput us on a calendar-year quarterly of many requests, we ll also three-holedrill Counter Pointso you can save the issues in a again, thank you for your support. We at WELLS look forward to being a valuablediagnostic and driveability resource to you formany years to on page 2continued on page 222Q: We have a 1988 Pontiac LeMans that is hard to start during rainy, damp weather. Replaced the spark plugs and plug wires which help somewhat, but problem still occurs. What s up? Charley Meyers, Ft. Wayne, INHard starting can be caused by condensation on theinner and outer surfaces of the distributor cap. Moisture drains off the ignition voltage and weakens the spark making the engine difficult or impossible tostart.

6 The buildup of moisture on the cap on this car can be made worse by the plastic-bag style splash shieldthat covers the cap on vehicles built before VINJB372711. Discard the splash shield, then remove thecap, wipe it dry and carefully inspect it for wear,burning, cracks or carbon tracks. Replace the cap and rotor if any defects are : A 1987 Ford Thunderbird with a engine idles rough and sometimes stalls. Checked intake vacuum, spark plugs, ignition timing, fuel pressure and compression. All are okay. Jose Raffiel, San Diego, CAAn erratic idle, rough running and stalling on this carmay be caused by chafing of the MAP sensor wires. The wires may rub against the engine-ground strap,creating a short, which may also set a code 22. Loosenthe engine ground-strap attaching screw and rotate theeyelet to a downward position so the strap does notmake contact with the MAP sensor wires.

7 Tighten theground-strap screw and repair the insulation on theMAP sensor : A 1991 Chevy Caprice with HEI ignition dies and won t restart (no spark). Replaced ignition module. Engine ran fine for several days, then died (again, no spark). Jeff Steiner, Columbus, OHDon t be too quick to blame the module. The problemmay be a faulty pick-up coil connector. The pick-up coilproduces a small current that the module uses to switchthe ignition coil on and off. If a poor connection existsin the pick-up coil circuit, the module may lose thetrigger signal causing the engine to die because of nospark. Repositioning the pick-up terminal leads whenthe module is replaced may temporarily restore theFine Tuningquestions are answered by Jim Bates, Technical Services Director. Please send your questions to: Jim Bates c oWELLS Manufacturing Corp.

8 , Box 70, Fond du Lac, WI 54936-0070 or e-mail him We ll send you a WELLS shirt if your question is published. So please include your shirt size with your question. FineFineTuningconnection. But if the female connectors on the ends ofthe pick-up coil wires are loose or corroded, the problemwill soon the green and white pick-up coil wires fromthe HEI module in the distributor. Check the continuityof the pick-up coil windings by connecting anohmmeter across the two terminals. A good windingwith tightly crimped terminals will produce a readingbetween 500 and 1500 the connectors on the wires and/or solderingthe connectors to the wires will help assure good , make sure the pick-up coil-wire female connectorsfit the spades on the HEI module tightly. Applydielectric grease to the terminal connections to : A 1995 Honda Civic misfires badly whenaccelerating.

9 One spark plug was found to be wet. Replaced spark plugs. Condition improved but still misfires occasionally under load. Wade Jackson, Lubbock, TXCheck the spark plug wires. Excessive resistance in theplug wires can increase the firing voltage requirements tothe Point where the spark may not be able to jump theelectrode gap when the engine is under load. Loose-fitting spark plug boots or damaged insulation onthe plug wires may also provide paths where the sparkcan escape to ground. Good plug wires should generallyhave less than 8,000 ohms per foot resistance. Ifresistance exceeds specifications, or the plug wires arefound to be damaged, replace the from page 1 making Sense Of Oxygen Sensorscontinued from page 3 When the engine is running in closed loop, a goodO2 sensor will produce a voltage signal that isconstantly changing back and forth from rich to transition rate is slowest on engines withfeedback carburetors, typically one per second at2500 rpm.

10 Engines with throttle-body injection are somewhat faster (two or three times per second at2500rpm), while engines with multiport injection arethe fastest (five to seven times per second at 2500 rpm).OBD II = MORE O2 SENSORSOn late model vehicles equipped with OBD II, thenumber of oxygen sensors used has doubled. Asecond oxygen sensor mounted behind the catalyticconverter is used to monitor converter operatingefficiency. The OBD II system does this bycomparing the fore and aft O2 sensor readings. Littleor no change in oxygen readings between both sidesof the converter can mean the converter isn t doinganything. This may cause the Malfunction IndicatorLamp (MIL) to come SENSOR DIAGNOSISO2 sensor performance diminishes with age ascontaminants accumulate on the sensor tip andgradually reduce its ability to produce voltage.