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Ford Truck Club Forum > GARAGE TALK > Garage Talk: Shop Class 101



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  #1  
Old August 29th, 2012, 10:56 PM
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Booba5185 Booba5185 is offline
 

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Default EFI Sensors and Definitions

Ever wonder what all the sensors are called and what they do? Here's some abbreviations and defintions of common sensors:
IAT (Intake Air Temperature) Sensor: The Intake Air Temperature (IAT) sensor resistance changes in response to the intake air temperature. The sensor resistance decreases as the surrounding air temperature increases. This provides a signal to the PCM, indicating the temperature of the incoming air charge.
The following symptoms can be caused by a faulty IAT sensor due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit.
Related Symptoms
  • Extended crank time when the engine is cold
  • Poor fuel economy
  • Spark knock
ECT (Engine Coolant Temperature) Sensor: The engine coolant temperature sensor resistance changes in response to engine coolant temperature. The sensor resistance decreases as the surrounding temperature increases. This provides a reference signal to the PCM, which indicates engine coolant temperature.
The following symptoms can be caused by a faulty Engine Coolant Temperature Sensor or circuit loose connections.
Related Symptoms
  • Extended crank time when the engine is cold
  • Poor fuel economy
  • Spark knock
  • Lack of engine power
  • Erratic and/or high idle
  • Engine cooling fan stays running all the time
  • Engine cooling fan fails to turn on
  • Engine overheating
TPS (Throttle Position Sensor): The Throttle Position (TP) sensor is a potentiometer which provides a signal to the PCM that is directly proportional to the throttle plate position. The TP sensor is mounted on the side of the throttle body and is connected to the throttle plate shaft. The TP sensor monitors throttle plate movement and position, and transmits an appropriate electrical signal to the PCM. These signals are used by the PCM to adjust the air/fuel mixture, spark timing and EGR operation according to engine load at idle, part throttle, or full throttle. The TPS is not adjustable.
A faulty throttle position sensor or switch due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit can cause the following symptoms.
Related Symptoms
  • Bucking
  • Hesitation
  • Stumble
  • Chuggle
  • Stalling on Acceleration
Heated Oxygen Sensor (H02S): The oxygen sensors supply the computer with a signal that indicates a rich or lean condition during engine operation. This input information assists the computer in determining the proper air/fuel ratio. A low voltage signal from one or more sensors indicates too much oxygen in the exhaust (lean condition) and, conversely, a high voltage signal indicates too little oxygen in the exhaust (rich condition). The oxygen sensors are threaded into the exhaust manifold and/or exhaust pipes on all vehicles. Heated oxygen sensors are used on all models to allow the engine to reach the closed loop faster.
A faulty oxygen sensor due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit can cause the following symptoms.
Related Symptoms
  • Surging at idle
  • Unstable idle
  • Running rough off idle
  • Hesitation
  • Stumble
  • Chuggle
  • Poor fuel economy
  • Spark knock
  • Stalling on acceleration
KS (Knock Sensor): The knock sensor is used to detect engine detonation (spark knock). As a result, a voltage sent to the PCM will retard spark timing. The KS is a piezoelectric accelerometer with the sensor designed to resonate at approximately the same frequency as the engine knock frequency. The KS uses the resonant frequency to mechanically amplify the vibrations. This method allows relatively large signals to be achieved without electrical amplification and with small package size.
To prevent the replacement of good components, be aware that the following non-EEC areas may be at fault:
  • Fuel (quality)
  • Fuel (octane)
  • Basic engine
  • Spark timing
IAC (Idle Air Control) Valve: The Idle Air Control (IAC) valve controls the engine idle speed and dashpot functions. The valve is located on the side of the throttle body. This valve allows the necessary amount of air, as determined by the Powertrain Control Module (PCM) and controlled by a duty cycle signal, to bypass the throttle plate in order to maintain the proper idle speed.
Related Symptoms
  • Stalls after start when engine is cold
  • Stalls after start when engine is hot
  • Stalling on deceleration
  • Stalls at idle
  • Unstable idle
  • Diesels or runs on after the engine is shut off
  • High idle
  • Low idle
MAF (Mass-Air Flow) Sensor: The Mass Air Flow (MAF) sensor directly measures the amount of air flowing into the engine. The sensor is mounted between the air cleaner assembly and the air cleaner outlet tube.
The sensor utilizes a hot wire sensing element to measure the amount of air entering the engine. The sensor does this by sending a signal, which is generated by the sensor when the incoming air cools the hot wire, to the PCM. The signal is used by the PCM to calculate the injector pulse width, which controls the air/fuel ratio in the engine. The sensor and plastic housing are integral and must be replaced if found to be defective.
The sensing element (hot wire) is a thin platinum wire wound on a ceramic bobbin and coated with glass. This hot wire is maintained at 392°F (200°C) above the ambient temperature as measured by a constant "cold wire''.
A faulty MAF sensor due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit can cause the following symptoms.
Related Symptoms
  • A no start condition
  • Stalls at idle
  • Surging idle
  • Extended crank time when engine is cold
  • Hesitation
  • Stumble
  • Chuggle
  • Poor fuel economy
VSS (Vehicle Speed Sensor): The Vehicle Speed Sensor (VSS) is a magnetic pick-up that sends a signal to the Powertrain Control Module (PCM). The sensor measures the rotation of the transmission and the PCM determines the corresponding vehicle speed. A faulty speed sensor due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit can cause the following symptoms.
Related Symptoms
  • Overheated transmission
  • Increased emissions
  • Poor fuel economy
  • Stalling on deceleration
  • Improper shift points
  • Cruise control inoperative
MAP (Manifold Absolute Pressure) Sensor: The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU). The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel metering for optimum combustion.
Related Symptoms
  • A no start condition
  • Stalls at idle
  • Surging idle
  • Extended crank time when engine is cold
  • Hesitation
  • Stumble
  • Chuggle
  • Poor fuel economy

That's it for now, I'll be adding more as time goes on. Keep in mind that your vehicle doesn't necessarily have all of these sensors, but if your vehicle has one of these sensors, this should help you diagnose it.


89 F-150 5.0l AOD 2x4, 3.55 LS(+4), Converted to HO Roller, 3g Alt, GT40Ps, Y-pipe, Rerouted PCV, Dual Taurus E-fans, Explorer Injectors, Remote ICM, DIY Cold air, Rubber Vacuum System, Tranny cooler, Remote Tranny filter, Saginaw P\S swap, F350 Brakes, more.



Last edited by Booba5185; August 29th, 2012 at 11:02 PM.
The Following 3 Users Like This Post:
adoporto (November 27th, 2013), bikertrash3531 (August 31st, 2012), ONELOWF (August 31st, 2012)
  #2  
Old August 30th, 2012, 10:38 PM
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Booba5185 Booba5185 is offline
 

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If anyone needs another sensor explained, just ask. I'll do my best to explain it or look it up and provide some information on it.


89 F-150 5.0l AOD 2x4, 3.55 LS(+4), Converted to HO Roller, 3g Alt, GT40Ps, Y-pipe, Rerouted PCV, Dual Taurus E-fans, Explorer Injectors, Remote ICM, DIY Cold air, Rubber Vacuum System, Tranny cooler, Remote Tranny filter, Saginaw P\S swap, F350 Brakes, more.


  #3  
Old August 30th, 2012, 10:44 PM
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You care to explain Sesnors?
  #4  
Old August 30th, 2012, 10:53 PM
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You're too young to understand, I'll tell you when you're older.


89 F-150 5.0l AOD 2x4, 3.55 LS(+4), Converted to HO Roller, 3g Alt, GT40Ps, Y-pipe, Rerouted PCV, Dual Taurus E-fans, Explorer Injectors, Remote ICM, DIY Cold air, Rubber Vacuum System, Tranny cooler, Remote Tranny filter, Saginaw P\S swap, F350 Brakes, more.


  #5  
Old August 31st, 2012, 08:10 AM
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Nice write up, thanks.
The tps can be adjusted, although it is factory set. The two mounting holes can be slightly drilled out to give a bit of rotation. The target voltage is as close to 1v as possible and can be pin pointed to .98-.99v easily.

98" F150 XLT/STX
4.6 4R70W
Heads & Cams, etc, etc
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  #6  
Old August 31st, 2012, 09:14 AM
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0.97 volts is actually the best voltage to have it set at. The sensor is so sensitive that you most likely will not need to drill out the holes. 1.00 volt is the maximum you want it set up, 0.92 is the minimum.


89 F-150 5.0l AOD 2x4, 3.55 LS(+4), Converted to HO Roller, 3g Alt, GT40Ps, Y-pipe, Rerouted PCV, Dual Taurus E-fans, Explorer Injectors, Remote ICM, DIY Cold air, Rubber Vacuum System, Tranny cooler, Remote Tranny filter, Saginaw P\S swap, F350 Brakes, more.


  #7  
Old August 31st, 2012, 10:21 AM
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bikertrash3531 bikertrash3531 is offline
 

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Quote:
Originally Posted by Booba5185 View Post
You're too young to understand, I'll tell you when you're older.
OUCH!!!



1994 F150 XLT ExCab SB 306, 4R70w, 8.8 3.55 open, MSD StreetFire coil, Taylor Siro Pro wires, MSD cap and rotor, 1.72 Roller Rockers, 2º cam advance w/ Cloyes Street True Roller timing set, Flat top Hyperutectic pistons, Flowtech Long Tube headers, Xpipe, High flow Magnaflow converters, Spintech XL Sportsman DIDO muffler.

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Old February 21st, 2013, 10:41 PM
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i found this to be very informative.

i do have a question though ... you refer to the PCM and the ECU; i was under the impression that these were 2 terms for the same part (what many of us call "the computer"). if i am wrong, please tell me where these 2 parts are located.

thanks again for this very helpful info.
  #9  
Old February 21st, 2013, 10:52 PM
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They do accomplish the same things, but a PCM implies that the transmission is controlled as well. Example: I have an AOD transmission which is not electronically controlled, so I have an ECU(Engine Control Unit). If I have an electronically controlled tranmission such as an E40D or an 4r70W, then I would have a PCM (Powertrain Control Module).


89 F-150 5.0l AOD 2x4, 3.55 LS(+4), Converted to HO Roller, 3g Alt, GT40Ps, Y-pipe, Rerouted PCV, Dual Taurus E-fans, Explorer Injectors, Remote ICM, DIY Cold air, Rubber Vacuum System, Tranny cooler, Remote Tranny filter, Saginaw P\S swap, F350 Brakes, more.


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Old February 21st, 2013, 11:00 PM
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I abuse the terminology for those all the time. if this were any other site I'd get flammed for it! :lol:



1994 F150 XLT ExCab SB 306, 4R70w, 8.8 3.55 open, MSD StreetFire coil, Taylor Siro Pro wires, MSD cap and rotor, 1.72 Roller Rockers, 2º cam advance w/ Cloyes Street True Roller timing set, Flat top Hyperutectic pistons, Flowtech Long Tube headers, Xpipe, High flow Magnaflow converters, Spintech XL Sportsman DIDO muffler.



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