Anyone know what the "Charge Temperature Switch" does on an '87 3.9LDak?

Discussion in 'General Motoring' started by Jack, Dec 28, 2008.

  1. Jack

    Jack Guest

    From the 87 Dakota shop manual:

    Charge Temperature Switch (CTS)
    (Used only on 3.9L engine)

    "The Charge Temperature Switch (CTS) is located on the intake manifold
    to the right rear of the carburetor. This switch monitors the intake
    charge (air fuel mixture) and feeds this information to the SCC (spark
    control computer) to prevent the EGR valve from opening when the intake
    charge temperature is below approximately 15°C (60°F)."

    The switch is there all right. The only problem with this is that the
    EGR valve on this truck is controlled only by a "Coolant Vacuum Switch
    Cold Closed". This is a sensor that opens and closes an air passage
    based on coolant temperature. There is absolutely no electricity involved.

    There is another coolant temperature sensor that feeds temp info to the
    computer to control the spark advance based on engine temperature.
     
    Jack, Dec 28, 2008
    #1
  2. Jack,
    The purpose of the switch is to alter the advance curve of the ignition, not
    operate the egr valve. The advance curve is also influenced by the engine
    coolant temperature as well. Some engines use detonation sensors in place of
    a CTS for the same purpose.
    Steve

    From the 87 Dakota shop manual:

    Charge Temperature Switch (CTS)
    (Used only on 3.9L engine)

    "The Charge Temperature Switch (CTS) is located on the intake manifold
    to the right rear of the carburetor. This switch monitors the intake
    charge (air fuel mixture) and feeds this information to the SCC (spark
    control computer) to prevent the EGR valve from opening when the intake
    charge temperature is below approximately 15°C (60°F)."

    The switch is there all right. The only problem with this is that the
    EGR valve on this truck is controlled only by a "Coolant Vacuum Switch
    Cold Closed". This is a sensor that opens and closes an air passage
    based on coolant temperature. There is absolutely no electricity involved.

    There is another coolant temperature sensor that feeds temp info to the
    computer to control the spark advance based on engine temperature.
     
    Steve Lusardi, Dec 28, 2008
    #2
  3. From the 87 Dakota shop manual:

    Charge Temperature Switch (CTS)
    (Used only on 3.9L engine)

    "The Charge Temperature Switch (CTS) is located on the intake manifold
    to the right rear of the carburetor. This switch monitors the intake
    charge (air fuel mixture) and feeds this information to the SCC (spark
    control computer) to prevent the EGR valve from opening when the intake
    charge temperature is below approximately 15°C (60°F)."

    The switch is there all right. The only problem with this is that the
    EGR valve on this truck is controlled only by a "Coolant Vacuum Switch
    Cold Closed". This is a sensor that opens and closes an air passage
    based on coolant temperature. There is absolutely no electricity involved.

    There is another coolant temperature sensor that feeds temp info to the
    computer to control the spark advance based on engine temperature.


    Reply: There should be a solenoid on the passenger side valve cover that
    supplies vacuum to the EGR valve, the computer controls this solenoid (using
    that charge temp sensor as an input) to prevent EGR from working on a cold
    intake (to prevent EGR from causing a stumble).
    There may be other solenoids on the passenger valve cover, one of them is
    for the air pump switching valve (if equipped).

    Tom from NY
     
    THOMAS SHOWERS, Dec 28, 2008
    #3
  4. Jack

    Jack Guest

    The part that alters the spark advance is called the "Coolant
    Temperature Sensor" and is located in the front left of the carb. It
    measures the temp of the coolant.

    The part I am inquiring about is referred to in the Ignition System
    section of the shop manual as the "Charge Temperature Switch" and is
    located in the intake manifold in the right rear of the carb. It
    measures the temp of the air/fuel mixture in the intake manifold.

    After posting the question, I found another reference to the Charge
    Temperature Switch in the Emissions section of the shop manual in which
    it is described as sending temp info to the computer to 1) allow pumped
    air to be switched from the exhaust manifold to the catcon and 2) allow
    purging of the purge canister.
     
    Jack, Dec 28, 2008
    #4
  5. Jack

    Jack Guest

    Tom, the EGR valve on this engine is controlled solely by vaccuum and is
    located on driver's side of the intake manifold. The EGR vacuum is
    supplied by a port on the carb and is routed through a "Coolant Vacuum
    Switch Cold Closed" that is closed when cold and open when warm. Refer
    to first answer on this thread for more info.

    Bottom line is the shop manual got it wrong in the ignition system
    section and got it right in the emissions section.
     
    Jack, Dec 28, 2008
    #5
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.