1971 CEC problem

[Gerard Q.]

My 71 350 small block will not come off it's secondary high idle. I've replaced the reversing relay GM 3990842 and the delay relay GM 3990843. In each case the CEC solenoid (GM 1114444) remains energized. If I unplug the green wire connector from the reversing relay the solenoid de-energizes. I believe I might have a bad thermal switch which is mounted in the RH cylinder head. Does anyone have the original or replacement part number or if anyone has some additional insight as to what might be causing this I would appreciate any advice.

BTW, the CEC system has worked perfectly for the past 10 years.

Thanks in advance,

Jerry Quinn

[Edward J.]

Re: 1971 CEC problem

Gerard, is your car a 4 speed? if so have you looked at the switch in the trans. I believe it energizes the CEC system when 4 gear is selected, maybe the switch is stuck on???

[Gerard Q.]

Re: 1971 CEC problem

Nope its a TH400 auto trans which like the 4 sp energizes the solenoid when in high gear. I guess it could be the culprit however I'm leaning toward the thermal switch which has 3 positions, 1-engine is cold, 2- engine is normal operation temp and 3-engine is overheating. In any case I need the part numbers and if anyone is reproducing them.

[Edward J.]

Re: 1971 CEC problem

Gerard, I have a 72 slightly different that 71 but believe the THM400 works the same, there is a orange/ black wire connector on the side of trans. the black wire is grounded by a pressure switch in the transmission, so if you just unplug the connector on the outside of transmission this should open the ground circuit and if this the cures the problem with the high idle, you'll want to drop pan and nose around inside, the switch is mounted to valve body, if the wire is not grounded any where I would replace the switch.

[Kevin G.]

Re: 1971 CEC problem

Jerry,

I'm wondering if it's simply the solenoid itself? I wouldn't think the temp switch is the problem as it's only function is below 83* or above 230* IIRC. Being certain the parts you have replaced are good the last, item would be the solenoid.
I'll take a look at my GM troubling shooting booklet, and get back unless someone else jumps in sooner.

[Edward J.]

Re: 1971 CEC problem

Kevin, that would be a easy test, by just unplugging the solenoid wire connector, and if the idle is still high, then the solenoid would be stuck on and then problem solved .

[Gerard Q.]

Re: 1971 CEC problem

Thanks Kevin...I was using the tbl shooting guide Jack Humphrey published in a chapter newsletter. It passes the tests for inoperative solenoid.
It states the solenoid should not energize with the ignition off and it does not. Once the ignition is turned on it does energize which is correct. If I had a color coded diagram that would be helpful in determining where the green wire connected to the reversing relay goes. Once I disconnect it the solenoid de-energizes. My hunch is it is the thermal switch lead which does energize the solenoid when the engine is cold or over heating.

[Gerard Q.]

Re: 1971 CEC problem

So I just went out and started the car (cold) with the green wire unplugged. Ignition off solenoid not energized. Ignition turned on (not start) the solenoid was energized, plunger extended. Started car and it went up to fast idle. After a number of minutes went to secondary idle and then to normal idle solenoid now not energized. So this green wire is what's keeping the solenoid operated......thermal or trans switch? I should also note the solenoid does not energize for 15 sec when starting a warm engine with the green wire disconnected which is the job of the delay relay which gets it's signal from the thermal switch..... one of the reasons I'm leaning toward that switch.

[Edward J.]

Re: 1971 CEC problem

Gerard, I seem to remember there was a restorer a while back with a dia. and testing for the 70/72 TCS/CEC systems. It was good reading as I had issues with my 72. before I went for flight judging with my 72. also the service manual was very helpful. Keep in mind that the solenoid is powered with key on and everything that activates it is a ground path to the solenoid,( temp switch cyl. head, trans. pressure switch)I think by unplugging the cyl. head temp switch or the transmission plug your taking each out of the equation. this could lead you to the problem if one of these are bad.

[Gerard Q.]

Re: 1971 CEC problem

Ed I agree....I'm hoping someone has the part numbers so when I do isolate the defective part I can to locate it.

[Jim M.]

Re: 1971 CEC problem

Jerry:

I believe the GM part number for the two blade thermal switch in the passenger-side cylinder head is 6489785. Good luck troubleshooting.

[Gerard Q.]

Re: 1971 CEC problem

Thanks Jim, I appreciate the help.