Auto Tap General Terminology
Work or energy that flows in response to any driving force other than a temperature difference, such as a force, a torque, or a voltage.1
Torque is the amount of work that can be accomplished.2
Horsepower is the amount of time that the amount of work can be done.2
Heat is energy that flows as a result of a temperature difference between a system and it's surroundings.1
Open Loop Operation determines the air/fuel ratio based on predetermined tables stored values. This happens when the low coolant temperature is low that the PCM will trigger fuel enrichment outputs to act like a choke for cold-start and warm-up situations.5
Closed Loop Operation determines the appropriate air/fuel ratio based on the amount of residual exhaust-gas oxygen measured by your oxygen sensors (02B1S1 & 02B2S1). Closed Loop Operation will be active when Open Loop Operation is not active.3
PCM stands for Power Control Module and makes decisions based on what information the sensors throughout the car report back.4
See Figure 1 below to see a general overview of how the PCM works. Notice that the picture says ECM, this also stands true for the PCM.
MAF or Mass Air Flow sensor measure's the amount of air that enters the engine. This gives the computer (PCM) more precise control over the air/fuel ratio.5 This is measured in pounds/minute (lb/min).
MAP or Manifold Absolute Pressure sensor reads the intake manifold atmospheric pressure. If this sensor is to fail the system will revert to a limp-home system.5
TPS or Throttle Position Sensor tells the computer (PCM) using a voltage signal how far the throttle-blade is open and the rate at which it is changing.5
WOT or Wide Open Throttle is when the gas pedal is floored. The TPS sensor should read 100% or over 4 volts for the value it reports to the PCM.
KR or Knock Retard is caused by vibrations in the engine block and detonation. In the event either of these are detected by a knock sensor and a signal is sent to the PCM and the PCM will reduce timing to protect the engine.
Detonation occurs when the air/fuel mixture is compressed and the temperature goes up. The more compression, the higher the temp. At some point, the fuel may spontaneously ignite prior to the spark plug firing. This is detonation and it is very bad for an engine because it often occurs just before the plug fires. You then end up with two flame fronts in the cylinder that crash into each other which can crack pistons and rings, etc.6
Octane is a measure of how much a given blend of fuel resists detonation.7
1. Felder, Richard M., and Ronald W. Rousseau. Elementary Principles of Chemical Processes. 2nd Edition. John Wiley & Sons, Inc.: New York, 1986. Pages 296-297.
2. Smith, Jeff. "Fuel Injection Basics, Part One." Fuel Injection Basics. Display until 12/6/99. Page 32.
3. Smith, Jeff. "Fuel Injection Basics, Part One." Fuel Injection Basics. Display until 12/6/99. Pages 16-17.
4. Smith, Jeff. "Fuel Injection Basics, Part One." Fuel Injection Basics. Display until 12/6/99. Page 6.
5. Smith, Jeff. "Fuel Injection Basics, Part One." Fuel Injection Basics. Display until 12/6/99. Page 8.
6. Schlorff, Brian. "Ocatne Explained." http://www.mit.edu/people/zimerman/Documents/tr6/octane.html
7. Vizard, David. How to Build Horsepower. Volume 2. Page 33.
Web Author: Eric Barger email@example.com
Copyright © 1999 - 2002 Eric Barger. All rights reserved.
Revised: June 07, 2007 .