Vote Yes on Driveability

Vote Yes on Driveability
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  Vote YES onDriveability I noticed several conversations atthe Nashville EXPO concerningdriveability issues.We could debate the question howdriveability affects our relationshipwith general repair shops in the area.Do they handle only the driveability problems and refer all the transmissionwork to you? Some do, but apparentlynot all. Most general repair shops andchains sell their customers on fluidchanges. Some also repair leaks, adjust bands, perform electrical testing andrepair, etc. They could also R&R a unitand install a reman.  Now you can vote to keep your relationships with other shops the waythey are or not. So, without getting inany deeper in this debate, let’s say youwant to expand your income without alot of expense. How can you? Theanswer is… you guessed it: driveabili-ty.You already have the same testersand hand tools they do. All you need issome reference material and knowl-edge. If you’re concerned about whatthe general repair shops might say, justtell them that driveability affects thetransmission and these repairs are nec-essary to make the transmission work.I believe it’s easier to understandand diagnose engine problems thanautomatic transmissions. Here is areview of all the basic theory andunderstanding a driveability tech downthe street has to know.Simply put, an engine producestorque to turn the transmission by ignit-ing a combustible mixture in anenclosed chamber. Amodern gas/dieselengine must also supply usable torqueover a wide range of RPM, with verylow emissions and high efficiency.Why do vehicles need transmis-sions with 4, 5 and 6 speeds?Efficiency. As good as modern enginesare, they don’t produce a lot of torque atlow RPM. Plus, people expect the vehi-cle to accelerate, cruise, pull hills, creepthrough parking lots, idle in gear, etc.In the old days of gas engines (30years ago), a distributor-mountedswitch fired a coil, which sent a highvoltage spark to each cylinder at theright time to ignite a mixture of fuel andair. Acarburetor mounted on a commonintake created this mixture in a ratio of 14.7:1, more or less.The thing worked, but not effi-ciently. To improve emissions, per-formance and economy, engineers andtechnicians at the factory took a newapproach. By using a computer feed- back system, they could duplicate thesame performance they achieved in thelaboratory in every vehicle that uses thesame engine design. Let’s look at the brains of this per-formance system, the Electronic 4GEARS November 2003 WHATNOW by Dave Skora Vote YES onDriveability  rive bility  Extreme Ride  is a revolutionary new material from Raybestos Powertrain that measurably increases clutch pack performance and durability. X-32 ™ is just one way Raybestos is aggressively leading the industry inintroducing innovative technologies. 964 East Market St., Crawfordsville, IN47933 ã Toll Free: 800-729-7763 ã Fax: 765-364-4576 ã Email:  Control Unit, or ECU. The ECU is incontrol of electromechanical and elec-trohydraulic devices. Some ECUs con-trol several devices, such as engine,transmission and ABS brakes. Other ECUs only control the engine and aretypically networked through a data link (serial or CAN) to other modules on thevehicle.Internally, ECUs share many fea-tures of a typical home PC. An internalCentral Processing Unit (CPU) processes the data. The CPU alsoincludes a permanent memory(firmware) which instructs the internaldevices what to do. The CPU constant-ly monitors circuits and vehicle opera- 6GEARS November 2003 Vote YES on Driveability Typical MAFF Sensor Typical MAF Sensor Readings  GEARS November 20037 tion for faults. Any faults detected arestored in the CPU as trouble codes.Most of today’s ECUs include aflashable memory chip, which storesthe software program. Another deviceinside the ECU converts analog inputsignals to digital. Based on the internal program, the ECU then controls theoperation of the engine, transmission,etc. If you would like to learn moreabout ECUs, there are books, and web-sites like Motorola and ACDelco,which have a lot more detail on thesubject.For the ECU to control the engine,it needs several input signals to process. Two of the main ones are anengine RPM signal and a crank or camshaft position sensor. As a rule,these are usually PM-type AC genera-tors or Hall Effect-type sensors. Thesesensors inform the ECU how fast theengine is turning and when the engineis positioned to fire the number onecylinder.But the ECU isn’t quite ready totrigger a spark. It still needs to knowhow much air is being drawn into thecylinders. Most systems use a ThrottlePosition Sensor (TPS) or Accelerator Pedal Position (APP) sensor, plus aMass Airflow (MAF) or ManifoldAbsolute Pressure (MAP) sensor. TheTPS/APPsensors are simple poten-tiometers. These sensors are very goodat informing the ECU how far thethrottle plate is open, especially at idle,during WOTacceleration or at steadyopenings.AMAPor MAF sensor providesthe ECU with a load signal, based onconditions such as coasting, pulling ahill, or startup. AMAPsensor measuresthe intake manifold vacuum and workson the principle of air density. MAFsensors measure the volume of air drawn into the intake manifold. Theyare typically mounted in the ducting between the air cleaner and intakeopening.With a couple of temperature sen-sors to monitor the ambient and enginecoolant temperature, and a BARO sen-sor to indicate altitude, the ECU is nowready to operate the fuel injector(s) andfire the coil. Based on the installed pro-gram, the ECU can operate the engineefficiently. This is a lot better than inthe past with virtually no accurateadjustments for temperature, altitude,or constantly changing vehicle loads.To improve the performance andefficiency further, the ECU also moni-tors two important conditions: ignitionand air/fuel mixture. Typically the ECU Typical Tempature Sensor Typical AC Generator 


Jul 23, 2017


Jul 23, 2017
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