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

From : steve lusardi

Q: 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 15c 60f. 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. .

Replies:

From : thomas showers

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 15c 60f. 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 .