2 WEL151 CounterPoint12 - Wells Vehicle Electronics

1 Damaged Spark PlugThese hot spots ignite the air-fuel mixturebefore the spark plug fires. The result is twoflame fronts, one from the hot spot and onefrom the spark plug, occurring at the sametime. The fronts slam into each other violentlyas the burning gases rapidly also occurs if spark timing isadvanced too far. In this type of situation,there is only one flame front, but it happenswhile the piston is too far before TDC. Instead of a collision between flame fronts,there is a collision between the rapidlyexpanding gases from combustion and the topof the piston as it moves up the cylinder an OBD-II system with electronic sparktiming, the PCM continually reads a numberof input signals, including base timing,throttle position, intake manifold pressure,transmission gear and Vehicle speed.

2 SomePCMs will even read a rapid change in throttleposition, indicating the driver wants toaccelerate quickly. Based on its programming,the PCM advances spark to a preset level fordifferent conditions. The preset spark advanceis typically close to the knock point becausethe system relies on the knock sensor as awarning knock sensors send a base or noknocking reference signal to the PCM. If knocking occurs, the sensor detects theincreased vibration and increases its signal to the PCM. The PCM then slightly retardstiming until the sensor signal returns to thereference level.

3 If a temporary condition caused the knock,the PCM will set spark timing to theprogrammed advance. If the knock returns,the PCM will cycle spark timing, advancingtiming until knock is encountered and thenretarding timing until the knock is conditions would have the spark occurwhen the piston reaches top dead center(TDC). The flame front would travel acrossthe combustion chamber for a complete burnof the air-fuel mixture just as the pistonreturns down the cylinder. Realistically, theair-fuel mixture takes longer to burn.

4 Thedifference is a fraction of a second and mustbe compensated for. As a result, advancedtiming is required. The design of thechamber and advanced timing generateoptimal performance in terms of power, fueleconomy, and reduced LIKE MARBLESUp to a point, more power can be producedin an engine by increasing spark advance. Buttoo much advance causes engine knock starts, performance decreasesand there is a risk of serious engine gets its name because it causesvibrations and banging in the knock causes a pinging noisethat sounds like marbles or small ballbearings bouncing on a piece of metal.

5 WHAT S INSIDE:Knock 1& 3 / FINE 2 / QUALITY POINTS: Wells Introduces New Product Lines Using Lead-Free 2 / HOT OFF THE WIRE: Wells Wins Its Ninth National Catalog Manager s Association Award, Publisher s 4 CounterCounterPointTHE ELECTRONIC, DIAGNOSTIC AND DRIVEABILITY 4 Issue 4, October 2000continued on page 3 Knock Sensors Do Two JobsSevere knock sounds like someone banging ona door. Mild knock reduces power, wastes fueland increases emissions. Severe knock candestroy internal engine parts including thepistons, connecting rods, exhaust valves, headgaskets and spark plugs.

6 Knock occurs when the air-fuel mixturedoesn t burn smoothly or is ignited too can be caused by hot spots in thecylinder, such as carbon deposits or sparkplugs that are too hot for the engine, or highcombustion chamber temperatures. Knock sensors play a dual role on OBD-II engines. Like other sensors, knocksensors monitor engineoperation to optimize addition, knock sensors protect theengine against power-robbing, andpotentially destructive, engine : On a 1997 Taurus L, DIS, automatic,with 40,000 miles, the engine starts andruns OK, but it will set codes P0303(misfire #3) and P0304 (misfire #4) after afew minutes of driving.

7 The scope shows noproblem with secondary ignition. Cylinders3 and 4 share a coil, which was replaced,but the problem continues. What now?South Hampton Shell, South Hampton, NJRecheck the scope readings and spark plugwire routing. When replacing a coil pack, youmay also want to check the spark plug secondary resistance can cause high RFIlevels, which can affect the vehicles wiringand trigger false misfire : We have a 1997 Chevrolet Malibu thatseems to have a carbon-tracking problem in the ignition coil housing. We replaced the housing and spark plugs some timeback, but not the coils.

8 The car is in for ahard starting/poor performance complaintand needs new coils. When we removedthem, we noticed that the carbon trackingwas back. The plugs look OK and so doesthe rest of the housing. The weird thing is, you can wipe off some of the carbontracking with a rag. What causes this?Will s Autoworks, Trenton, NJMany ignition coil housings from the Quad4 and Twin Cam engines can develop acharacteristic marking that is often mistakenfor carbon tracking. These marks are acharacteristic of the high voltage distributionthrough the coil housing that can develop over a period of time.

9 Vehicle operation andclimate are also a factor. These false carbontracks, which can be wiped off with a dampcloth, can be often seen on the bottom of thehousing between the secondary ignitionterminals. Real carbon tracking from a highvoltage arc is characterized by damage to thecoil housing with black residue or carbonimbedded in the housing material. This typeof damage can not be wiped away very well,and can often be felt as well as : We have a 1996 Ford Aerostar, Lengine and automatic, that keeps setting aDTC P1443 (Evaporative Emission).

10 The firsttime, we ran the diagnostic procedure, wereplaced the evaporative canister purgesolenoid, and cleared the code. But P1443returns after the van has been driven for about an hour or so. Repeating thediagnostic procedure doesn t turn up anyother problem. What do you think?Phil s Mobil Service, Denver, COBe sure to check the fuel tank filler cap sealcarefully. The P1443 DTC can also be set byproblems with the purge flow sensor. If thecode keeps coming back, but the diagnosticroutine doesn t uncover a problem, be sure to check the purge flow sensor as 1997 Ford Taurus L keeps settingmisfire codes.