by Joe (Rigdonj) » 08 Jul 2002 22:05
Q: My Challenger did not come with an idle solenoid and I am having some trouble understanding how this thing is supposed to work.
A: It's simple. When the ignition is on then power is applied to the solenoid and extends it's plunger upwards. The fast curb idle speed adjustement screw on the arm on the curburator sits against the top of the plunger and you adjust the idle speed (900 RPM) with it. But when you turn off the ignition, the plunger retracts and the carburator closes even further to a position BELOW the normal idle speed position. This helps cut off the air and fuel flow into the engine and helps stop "run on" or dieseling.
1. Is this solenoid necessary?
No, not really. In IIRC this was only used on a few 1970 cars. It was required in California but not on the other 49 state cars. Starting in 1971 it was used on all cars.
2. What is its' actual function?
Above.
3. Where on the harness should I look for the connector?
The only schematic that I have that shows it is for a 340 4 bbl engine. On that one it's a dark blue wire and it comes from the I (field) terminal of the altenator.
4. Should the solenoid plunger activate with the key off or key on?
It extends (activates) with the ignition on. It retracts by spring pressure when the ignition is off.
NOTE: Some (all?) solenoids have two terminals, one at the top of the plunger and another at the bottom of the solenoid. Use the one at the bottom. The top one is is for an ignition timing retard system. This one shorts to ground via the carburator arm when the trottle is closed so make darn sure that you don't connect the blue wire there. Or you'll let the magic smoke out of your wiring harness!