Counterounter Point - Wells Vehicle Electronics

1 These programs use dynamometers to checkvehicle emissions under simulated drivingconditions. So knowing how to diagnose theEGR system when a NOX failure occurs shouldreduce the unnecessary replacement of EGR , a little background: the basic concept of EGR hasn t changed since it was introducedback in 1973 to meet federal emissionregulations. An EGR valve is used to open asmall passageway that connects the intake andexhaust manifolds. Intake vacuum then siphonssome exhaust back into the engine to dilute theair/fuel mixture. This lowers combustiontemperatures to reduce the formation of also helps the engine resist detonationunder load. (A typical earlier-style vacuumEGR valve is shown in Figure A.)

2 When the EGR valve opens, it has much thesame effect on engine performance as avacuum leak (idle roughness, leanmisfire and hesitation). For this reason,the EGR valve should not open until theengine is warm and above idle speed. On earliervehicles with vacuum-operated egr valves , a ported vacuum switch prevents vacuum from reaching the EGR valve until the engine is the 1980 s, computer-controlled solenoidsbegan to replace vacuum switches in EGRsystems. By monitoring engine speed,temperature, load, throttle position and vehiclespeed, the computer varies the duty cycle (ontime) of the EGR solenoid to vary the amountWHAT S INSIDE:Diagnosing Digital EGR 1& 3 / FINE 2 / QUALITY POINTS: These CAPS Are Lightweight & Tough.

3 Page 2 & 3 / HOT OFF THE WIRE: Wells Catalog Judged The 4 / Publisher s 4 CounterCounterPointTHE ELECTRONIC, DIAGNOSTIC AND DRIVEABILITY 3 Issue 4, October 1999of EGR as well as when it occurs. Some EGRvalves (Ford mostly) from this generation have avalve position sensor that provides additionalfeedback to the computer about how much EGRthe engine is the 1990 s, electronic (digital) EGR valvesbegan to replace vacuum-actuated EGR valvesbecause they can respond much faster to changesin operating conditions and work independentof intake vacuum. Several different types are used: Single-stage(A single solenoid is used to openthe exhaust passageway valve). The computermonitors various sensor inputs to determinewhen EGR is needed, then cycles the EGR valvesolenoid on and off to control the amount ofexhaust gas recirculation.

4 Multi-stage(Used on various late-modelGeneral Motors applications, this type has twoor three solenoids that open separate exhaustpassageway valves . See Figure B.) With thissetup, the computer uses a step strategy toincrease EGR in stages. If only a little EGR isneeded, one solenoid is energized. As more EGRis needed, the second and third solenoids areenergized. On the three-solenoid applications,up to seven different combinations may be usedto control EGR flow. Linear(Uses a small stepper motor instead ofsolenoids or a vacuum diaphragm to open theexhaust passageway valve). A linear EGR valveworks much like an idle-speed control motor inthat it moves in small increments. This allowsthe recirculation of exhaust gas to be increasedor decreased with a higher degree of on page 3 FIGURE AFIGURE BSOLENOID &MOUNTINGPLATE ASSEMBLYEGR BASE PLATEEGR BASE GASKETINSULATORGASKETSCREWASSEMBLYARMATU REASSEMBLYEGR BASEE xhaust gas recirculation (EGR) is used on most engines to reduce the formation of oxides of nitrogen (NOX) in the exhaust.

5 NOX is a pollutant that is now monitored by a growing number of enhanced emissions testing DigitalEGR ValvesThese CAPS Are Lightweight & Tough2 Distributor caps and rotors may seem like a generic product to some. After all, mostreplacement caps and rotors look pretty much the same. But appearances can bedeceiving because the performance of thematerials from which these parts are made can vary a leading supplier of original equipmentignition components, Wells engineers havethe inside track on what works and what doesn caps and rotors must meet rigorous teststandards for performance and durability. That s why Wells uses a special lightweightthermoplastic polyester resin in its OEM andQualityaftermarket distributor caps and rotors thatoutperforms the heavy, mica-filled componentsof thermoplastic polyester resin that Wells uses has outstanding chemical resistance to oil,gasoline, underhood chemicals and otherautomotive fluids.

6 It also has excellentdimensional stability. The dimensions remainstable regardless of temperature, humidity or chemical attack, so the parts fit correctlywhen they re installed, and continue to fitperfectly for years to caps and rotors have very low moisture-absorption characteristics resulting in superiordielectric strength. This allows them to betterQ: We have a supercharged 1995 PontiacBonneville VIN 1 that has a surge atidle with codes P0131 and P0171. We havechecked the O2 sensor, fuel pressure,timing, and vacuum hoses and connectionsfor leaks. The ISC counts are low but seemto be okay at around 13 or 14. This cardoes this all the time and temperatureseems to have no effect. Stevens Shell, Elizabeth, NJWith your scan tool connected, if the ISC counts stayless than 15, and the long/short-term fuel trim remainsgreater than 140, you should expect an air leak.

7 Oneplace you didn t mention checking was the superchargeroutlet gasket. Check for leaks, especially around thepulley end, as this is a common area for leakage to : I have a 1996 Buick Skylark with SFI that has a problem with a roughidle, repetitive stalling and hard problem is very intermittent and onlyseems to happen after the car has beensitting for a while, like overnight, andseems worse in colder weather. Scan tooldata seems to check out OK, but sometimes there are misfire codes (P0300 throughP0304). Any suggestions? Bill Renton, Billings, MTIf you haven t checked the oil pressure, you should do so,as there have been reports of the type of problem you arehaving due to excessive oil pressure caused by a stickingrelief valve.

8 This would cause the lifters to raise the valvesoff of their seats, resulting in a loss of compression andengine misfire and/or stalling on initial start-up. Tocheck this, install an oil-pressure gauge that can read atleast 150 psi in an oil pressure port and check the oilpressure at 3000 rpm. The oil pressure should not exceed100 psi even in very cold operating conditions andshould not exceed 85 psi with the engine warmed up tooperating temperature. If the oil pressure exceeds theselimits, you will have to replace the oil pump cover thathas an improved pressure relief : I am working on a 1997 Chevy Astrowith the VIN W engine. This van has anintermittent stalling condition and lousyperformance and has a DTC cap, rotor, coil, plugs, plugwires, engine vacuum, compression, fuelpressure are all good.

9 Cam and crankposition sensor signals are consistent. The primary wiring and connectors have all been checked as well. The engine runsgood at idle and in gear most of the time,but when driven, performance is poor. Any ideas? Brian Williams, St. Louis, MOCheck the ignition coil wires where they attach to theprimary terminals. These wires can get brittle near theconnector and the wire strands can break inside of theinsulation and not be easily detected. This can causereduced primary current flow, resulting in engine misfire under load. Eventually, all of the strands canbreak resulting in a no-start : We are working on a 1995 ChryslerConcorde with a MFI. The problem we are trying to fix is an extremely richmixture.

10 You can smell the gas in theexhaust. No codes. Injection goes from ms right at start-up and doesn tchange with propane or induced vacuumleak. I used both a scanner and a scope toverify that injection was really what wasindicated. The scanner shows MAP output to be volts at idle, but I can t find anyinformation for voltage specs for Chryslerfrom idle to WOT that we can use forreference. Thanks for any help. George Mills, Atlanta, GAThe MAP sensor should read about volts with thekey on, engine off (KOEO) at sea level and about or so at about 20 of vacuum. Since the averagevacuum at idle is about 17 to 23 , a MAP output volts is too high. Besides a defective MAP sensor orcracked sensor housing, be sure to check for damagedgaskets, hoses, EGR, ignition or cam timing, enginemechanical damage, etc.