Author Topic: Dodge TBI Info (work in progress)  (Read 26813 times)

0 Members and 1 Guest are viewing this topic.

Offline s ǝoɾ

  • Global Moderator
  • RCC Addict
  • *****
  • Posts: 24881
  • Gender: Male
    • The Best Offers!
Dodge TBI Info (work in progress)
« on: January 1, 2010, 07:25:48 pm »
Next part in the series.

Dodge TBI sensors

First, a look at their general locations:





***Note***:
1. The ECT is not to be confused with gauge cluster temp sending unit. The ECT does NOT control gauge. Has 2 wires as opposed to only 1.
2. The MAP may be remote located on firewall.
3. The Hall Effect sensor is located inside of distributor. Distinguished with round 3 wire connector. NO vacuum advance.
4. The 02 sensor is located in left side exhaust manifold.
« Last Edit: May 18, 2010, 08:14:35 pm by s ǝoɾ »
Avoid replacing any part that you have not proven to be faulty through extensive testing.

Best Auto Insurance | Auto Protection Today | FREE Trade-In Quote

RamChargerCentral

  • Advertisement
  • ***

    Offline s ǝoɾ

    • Global Moderator
    • RCC Addict
    • *****
    • Posts: 24881
    • Gender: Male
      • The Best Offers!
    Re: Dodge TBI Info (work in progress)
    « Reply #1 on: January 1, 2010, 08:21:37 pm »
    GLOSSARY

    ASD Relay- auto shut down relay. This relay controls the 12v POS side of coil, fuel injectors, and fuel pump. Upon first turning key to "on", the relay is turned on for 2 seconds. If the engine is not immediately cranked, the relay is turned off, killing these devices. Hall effect is used to sense "cranking" or "running", and PCM commands the relay. Important to note that both fuel and spark are controlled by this relay.

    ECT- engine coolant temperature sensor. 2 wire NTC thermistor. Has a ground, while other wire serves as both 5 volt reference AND signal. Resistance AND voltage goes DOWN as temperature goes UP. Reports coolant temperature to PCM to alter fuel/spark as temperature varies. Does NOT report to gauge. The varying resistance produces a variable voltage depending on temperature. 0-5 volt range. -40*-248*F.

    Hall Effect
    - a type of crank position sensor. Measure engine rpm, and crank position. Also a 3 wire sensor, but running on 8 volts. This sensor is very unique in the fact it is "digital", and does NOT produce a variable voltage. It is much similar to the old "points" style ignition, in the fact it only produces a "on-off" switching effect for each plug firing event. The difference is, the lack of physical contact. Since the plugs are firing thousands of times per minute, this is very difficult to catch with multimeter.

    MAP- manifold absolute pressure sensor. A sort of electronic vacuum gauge. 3 wire sensor sensor. Ground, 5 volt reference, and signal. Measures the load placed on engine. Ranging from nearly 30"Hg-atmospheric pressure. Also used upon first start up to measure barometric pressure. Compensates for altitude and weather variations.

    O2 sensor
    - oxygen sensor. Just as the name states, this sensor ONLY senses oxygen. NOT absolute air/fuel ratio. It is a galvanic battery, producing it's own variable voltage 0-1volt. Higher voltage, less available oxygen in exhaust stream. Used to control fuel ratio in certain cruise/low load applications after exhaust is heated to 600*. 1 wire sensor, although many have additional 12v heater wires to expedite reaching the 600* area.

    PCM- powertrain control module. The PCM is the computer or brain responsible for translating various sensor feedback into actions, turning on/off various devices as need be. Located behind the battery. PCM also regulates battery voltage into lower level 5/8v supply lines for sensor usage, and provides a return ground path.

    SENSOR- These devices only measure parameters, and turn this into a readable electrical signal for use by the pcm. They do not move (on their own), nor do they directly control anything. They do not think, they are just an observer or messenger. They report to the PCM, and the PCM uses their input to make decisions to control actuator/outputs such as EGR solenoid, fuel injector, coil, alternator, transmission, relay, and/or cruise control.

    SIG- signal voltage. The voltage or wire used to deliver info FROM sensor back to PCM


    TBI TS
    - throttle body temperature sensor. Perhaps the most overlooked and least important sensor of all...until it fails. Nearly identical to the ECT in specifications. Function semi limited, mostly hot-start compensation, a form of vapor lock protection. May also be used by pcm to verify ECT function upon startup. Common sense will say the coolant and throttle body should read similar.

    TPS- throttle position sensor. Just as the name says, this 3 wire sensor measures throttle opening. As with most other 3 wire sensors, it also runs on ground, 5volt reference, and signal. Ranging from 0-5 volts.

    VREF- reference voltage. This is the voltage/wire supplied TO a sensor to be altered into an output. A constant voltage, usually 5 or 8v.

    VSS- vehicle speed sensor. This sensor is actually a small generator, producing electricity from motion against magnetism. A 2 wire sensor. Just like other generators, this sensor produces AC voltage that varies depending on speed. The faster it spins, the more voltage is produced.
    « Last Edit: January 1, 2010, 09:47:32 pm by joe s »
    Avoid replacing any part that you have not proven to be faulty through extensive testing.

    Best Auto Insurance | Auto Protection Today | FREE Trade-In Quote

    Offline s ǝoɾ

    • Global Moderator
    • RCC Addict
    • *****
    • Posts: 24881
    • Gender: Male
      • The Best Offers!
    Avoid replacing any part that you have not proven to be faulty through extensive testing.

    Best Auto Insurance | Auto Protection Today | FREE Trade-In Quote

    Offline s ǝoɾ

    • Global Moderator
    • RCC Addict
    • *****
    • Posts: 24881
    • Gender: Male
      • The Best Offers!
    Re: Dodge TBI Info (work in progress/PM for corrections)
    « Reply #3 on: January 1, 2010, 09:22:12 pm »
    Circuit Failure

    The troublecodes in no way shape or form automatically indicate sensor failure. As a matter of fact, more often than not, the sensor is fine.

    The PCM cannot know a sensor has failed, only that it did not receive expected signal.

    This is especially critical when a number of sensor trouble codes appear simultaneously. Did all sensors mysteriously fail at the same time? Perhaps. Looking at the supply or reference voltage, we notice that most sensors receive a 5 volt input. This 1 wire provides multiple sensors with the voltage they need. If it is damaged, it may take all sensors down at the same time, or atleast provide false outputs.

    Failures generally tend to be one of a few types. Open circuit, short to power, or short to ground.

    Open circuits or high resistance is where voltage is cut off from the rest of the system due to corrosion, loose connectors, or breaks in the inside of the wire. These may alter voltage readings either higher OR lower, depending on sensor type and which wire is damaged.

    Shorts. Simply put, electricity going where it is not supposed to. Since the reference voltages used are of minimal voltage, these are not usually the fusible link blowing, fire starting shorts you would commonly think of. They may happen in a number of different ways.
    • Nearby 12v wires bleeding into a reference or signal wire
    • Reference bleeding into signal wire, producing false high reading
    • Reference or signal wire shorting to ground, producing a false low reading and/or damaging components
    Avoid replacing any part that you have not proven to be faulty through extensive testing.

    Best Auto Insurance | Auto Protection Today | FREE Trade-In Quote

    Offline s ǝoɾ

    • Global Moderator
    • RCC Addict
    • *****
    • Posts: 24881
    • Gender: Male
      • The Best Offers!
    Re: Dodge TBI Info (work in progress/PM for corrections)
    « Reply #4 on: March 16, 2010, 01:54:31 am »
    Fuel System PartI

    The part of the system responsible for getting fuel from the tank to the intake manifold.

    Pump is of the 12volt electric type, in tank. In reality, the pump runs at similar voltages to the charging system, and each volt less than full charging voltage significantly decreases output. More voltage=more power for pump. Having 11 or 12 volts at the pump terminal may seem sufficient, but indicates up to 3 volt loss throughout the wiring circuit.

    The pump DOES NOT run at all times the ignition switch is in the on position. This could result in a fiery accident. Instead, it turns on for ONLY 2 seconds to help prime the system, and then remains off until the engine is running. This is VERY important to keep in mind. The system used to control pump function is known as ASD relay.

    ASD relay uses PCM monitoring of the hall effect sensor. It recognizes the engine is turning and powers on the pump. In case of an accident where a fuel line is severed, if the pump ran at all times, it would continue to spray fuel all over potentially hot catalytic converters. With the ASD system, the engine will quickly stall from lack of fuel, and the pump will shut off due to the stalling condition.

    This system runs 14.5psi +/- 1psi. 13.5-15.5 in other words. The pump is a positive displacement type which produces excess volumes of fuel. Pressures would quickly rise well over the limit if something was not in place to limit the pressure. If the pump was sized correctly for idle, it would not provide sufficient fuel for wide open throttle or various other partial-loads. Hence the pressure regulator comes into play.
    « Last Edit: March 16, 2010, 01:56:12 am by joe s »
    Avoid replacing any part that you have not proven to be faulty through extensive testing.

    Best Auto Insurance | Auto Protection Today | FREE Trade-In Quote

    Offline s ǝoɾ

    • Global Moderator
    • RCC Addict
    • *****
    • Posts: 24881
    • Gender: Male
      • The Best Offers!
    Re: Dodge TBI Info (work in progress/PM for corrections)
    « Reply #5 on: March 16, 2010, 01:57:12 am »
    Fuel System PartII

    The regulator has what appears to be a vacuum line. This is NOT a vacuum line, nor should it be hooked to a vacuum source. It simply collects vapors from a failing regulator for emission purposes. It could fail in a number of ways. The rubber diaphragm inside can rupture, thus causing a fuel leak. That vapor hose will then be filled with fuel. If the hose ever has ANY drops of fuel, the regulator is automatically condemned. The regulator may stick closed, thus resulting in excess pressure. This will cause an excessively rich idle that may slowly clear with increased load/WOT. The regulator may also stick partially open. This will result in low fuel pressure and no residual pressure. This can cause a no-start condition and/or engine that operates increasing worse with rpm/load, resulting in stalling or limited power.

    The fuel filter is a very simple device that is often overlooked. It does nothing fancy. It filters fuel. If clogged, it limits the amount of fuel reaching the engine. No need to test it. They are simple and cheap, replace it. The intank fuel sock could be considered a filter, restriction may cause obvious delivery concerns.

    The fuel lines can be a very pesky part of troubleshooting. Depending on which side of the fuel pressure regulator they are on (feed or return), they may simulate regulator failure. A pinched feed line restricts pressure. A pinched return line increases [back] pressure. The hardest of all, is a 8" piece of corrugated clear tubing inside of the tank, between the pump and top of sending unit. If this piece develops a leak, it will only leak back into the tank, NOT on the ground. This may also cause no start issues or low pressure concerns.

    While very rare, it is possible that the throttle body casting itself has flaws or cracks, allowing an internal leak or bypass.

    Finally, there is the fuel injector. An actuator that crosses the mechanical and electrical bridge. From the mechanical side, they may leak, seize/stick, or become clogged. Electrically speaking, they have a switched hot that runs from the same circuit as the fuel pump (ASD relay). They pcm controls the ground, which is rapidly pulsed to produce a fine mist in a conical pattern. The internal windings may burn out (open), gain resistance (impending failure), or short circuit.
    Avoid replacing any part that you have not proven to be faulty through extensive testing.

    Best Auto Insurance | Auto Protection Today | FREE Trade-In Quote

    Offline s ǝoɾ

    • Global Moderator
    • RCC Addict
    • *****
    • Posts: 24881
    • Gender: Male
      • The Best Offers!
    Re: Dodge TBI Info (work in progress/PM for corrections)
    « Reply #6 on: March 16, 2010, 02:14:11 am »
    Fuel System PartIII

    Previously, the term "residual pressure" was used. Residual pressure used to be called "prime"...as in priming the system, or losing prime. This is the system's ability to hold fuel pressure even after the engine is shut off. Just like a kitchen faucet. Even after you shut it off, it remains under pressure, instantly ready for full use at your next convenience. Those who have a well, know the pump does not run 24/7, or else you would have a huge electric bill.

    This is important for starting, especially since the pump only runs for 2 seconds BEFORE the engine is running. In a system that holds pressure, 2 seconds is plenty enough time. In a system that leaks down, 2 seconds may not be long enough to build sufficient pressure. Knowing that each key cycle delivers a 2 second on time, you may cycle the key multiple times before enough pressure is built up. This often results in hard starting/no starting in the morning, which does not occur, or gets better through out the day. This can be incorrectly associated with temperature, when in fact it is really related to how long the vehicle sits unused.

    With a pressure gauge hooked up, the system should maintain the pressure for a minimum of 5 minutes w/o dropping, after the engine has shut off. Ideally, it should not drop at all, but due to dirt and wear, the check valves do not provide 100% sealing.

    Any kind of leak may cause this loss of prime or residual fuel pressure. This could be an injector that does not completely close. A folded paper towel might be placed under the injector WITH ENGINE OFF to observe any leakage. A regulator may leak through the diaphragm or bleed through the return line. Various lines may leak internal or externally, so can the throttle body casting. An external leak is of the obvious type, the kind you can see leaving a puddle and gasoline odor.

    The pump itself also has a check valve to hold pressure. Essentially it is possible to have a pump that works to spec, moves fuel just fine, but is still defective due to in-op check valve. This is non serviceable, and the pump or sending unit module must still be replaced.
    « Last Edit: March 16, 2010, 02:18:12 am by joe s »
    Avoid replacing any part that you have not proven to be faulty through extensive testing.

    Best Auto Insurance | Auto Protection Today | FREE Trade-In Quote

     

    email