bwizeman

I have read the posts that talk about the idle solenoid on the early 70's cars. My understanding is that in '72 the idle solenoid was used to boost the idle rpm for AC cars under load of the compressor. Apparently in later years the solenoid was used for anti-dieseling.

Anyway, the wire runs along the intake manifold / valve cover edge and leads to the idle solenoid has 12V on it all the time... even when the ignition is off. My last idle solenoid melted. After I discovered it and disconnected it the battery stopped draining which was nice

I suspect that the ignition switch is bad based on a review of some recommended wiring diagrams, but am looking for confirmation that I am on the right track before I head off into the weeds.

Thanks,
Bill

Shark Racer

I don't know why the idle solenoid would be used "all the time". At that point you should just up the curb idle.

Mooser

Definitely shouldn't have power "all" the time, regardless of it's function on your engine.
My 72, BB w/o air it gets power with the key on only.
Mooser

bwizeman

I am totally with you guys... should not have power on that wire at all the times. Trying to figure out what could be the issue that is creating that condition.

bwizeman

BTW, I don't even have the idle stop solenoid on the car right now. Runs fine, don't really need it, but I'd like it to be "right".

71406

While the idle stop solenoid can be used for anti-diesel or to boost the idle speed when the compressor is on, when I installed a solenoid on my 71 its only purpose was to hook up the power to the AC compressor (I think the dark green wire). So when the compressor is energized the solenoid is energized and idle bumps up just enough to ensure idle stays the same weather or no the AC is on.

73, Dark Blue 454

The solenoid was needed to prevent dieseling. Without the solenoid, running an A/C compressor will mean the primary throttle blades are much more open to achieve correct curb idle which can cause dieseling (transition slots are uncovered alllowing fuel to be sucked into a hot chamber). The solenoid's plunger releases when the ignition is shut down allowing the PTB's to fully close and prevent dieseling.

Adjust the curb idle with the plunger and make sure the curb idle setting on the carb is out of play (you can remove the carb's adjustment screw entirely), and you'll never have to worry about dieseling.

Peterbuilt

What circuit is the idle solenoid protected by?
Can any one post a schematic or describe the circuit.
Thanks.

Mooser

Looking at the schematic for the 72 from the Haynes manual
The tan wire from the solenoid goes back/over and connects to a tcs connector which adds a dbl wire from the temp sensor. a separate blue wire comes up from the transmission
The Tan and dbl go into the firewall bulkhead and the tan, dbl and blue wires all go over to a TCS Delay Relay. RPO LS5 has a shorting bar instead of the relay.
From the relay, a single 20g yellow wire up to a connector, taps into a pair of Pink wires, one to the fuse panel, the other to the backup light switch. a 14 ppl goes up into the column, I suspect to the ignition.

The tcs relay is the one on the firewall between the brake and the wiper motor (pretty sure).

If your getting power constantly to the solenoid, check that relay and see if it's not the problem, looks like it might be stuck on all the time instead of only when the ignition is on.

HIH
Mooser

Peterbuilt

Mooser: Great explanation of a very complicated system. Found this while trying to figure it out.
http://www.73spot.com/index_stats_fi...ission/tcs.htm

Bwiseman: Could be a bad relay or as you suspect a problem with the ignition switch, you'll have to test each component and the wiring.
Temporarily if you want to use the idle stop solenoid you can run a new wire from it to a "Switched" terminal in the fuse box.

bwizeman

Thanks guys... this helps. I have some work to do! Will keep you posted.