CraigH

I think I may have the possible logic now after discussing it with my electrical Guru.

Limiting his options to 40 year old electrics was the first step.

The brown/white wire has some form of resistance etc to lower its voltage from 12 to @6-7 volts and that feeds the heat coil around the bi-metal strip in the time delay relay.

The heating coil has a specific resistance to earth/ground.

The pigtail harness that connects to the temp sensor also possibly has a specific resistance that is LOWER than the heater coils resistance.

So when the temp sensor grounds on low or high temperature the least resistant path to ground wins and the heater coil looses voltage, the bi-metal strip cools down and re establishes the contact causing the cec solenoid to fire.

This could explain why the CEC temp sensor pigtail was not part of the full engine harness and why it is a specific length and thickness. Way longer than needed to connect to the harness.




It would dissipate heat while it is providing a path to ground just like the heater coil in the time delay relay would, when it provides the path.

So now I need to get one of the pigtails and finish the job, hopefully understanding how it works.

...Roger...

Craig,are you getting ready for a PV test ?
I have a 70 in the shop that's going for it's PV test in Sept.

...Roger...

Since were on this subject , is the 70 supposed to react like the 71 in that when the engine is under 82 degrees the dist gets vacuum thus kicking up the idle ?

On the thermo switch is a green paint dot , is this supposed to mark the 230 degree spade and the unmarked spade is 82 degrees ?
TIA.

CraigH

Not sure what a PV test is but am assuming it relates to checking your Pollution gear on the car.

In Australia they dont really test any of this stuff for a car of its age.

For me it was more about understanding how it worked than needing to get it working if that makes sense.

Alan 71

Hi Craig,
I always wondered why the pigtails (both original and reproduction) were so long. You see all sorts of schemes used to run the wire around 'things' to take up it's length. I can't imagine that the pieces of tape lasted very long in the engine compartment's enviornment.
Thanks very much for the info!
Regards,
Alan

CraigH

Hi Roger

71 is unique in its overall operation from what I have read, however the thermo switch could be the same between a number of years and used to trigger similar operations to aid warm up or reduce emissions during certain temp ranges and driving conditions.

One of the issues I had were that the 71 AIM diagrams show 70 CEC/TCS items - THE 71 CEC must have been a very late change.

From the NCRS doc mentioned earlier it stated that only after some GM bulletin updates were diagrams corrected for 71.

As for the green dot , I have not seen a dot on mine but it could still be a bit dirty.

Whatever one is grounded when cold should be the under 82 spade I imagine if the switch is operating properly.

...Roger...

I hope I have the "PV" right. The test is the NCRS Performance Verification test. The one I'm working on is going for this test in Sept. and lots of things need to work correctly. I have the NCRS PV book and the 70 , 71 and 72 differences have me wondering a bit.
I'm wondering if the 70 should have the 82 degree idle RPM increase.
The switches could be the same but the jumpers could be different eliminating the 82 increase ( and this car has a new jumper).
Well I don't want to hyjack , did you get all your questions answered ?
If not ,and because I have this car here and partially apart, if I can help let me know.

edit-One little thought for those of you with a working TCS system, if your temp starts to increase while sitting in traffic , push the clutch in and put the shifter in 3rd or 4th. The advance should help cool the motor down.

CraigH

Hi Roger

I feel that I have the model understood now for 71.... or at least i have a very plausible/likely model.

Mine works 100% as I expect but I am missing the pigtail lead. Having it would not change the operation just the specific resistance of that path to ground (My harness wire may have been heating up during the testing more than designed without the pigtail :-)

Sounds like you will need to do a similar exercise to be 100%.

You are correct that If 70 did not have the delay timer there could have been other differences as well.

CraigH

Final Diagram for 71

Alan 71

Hi Craig and Roger,
Thanks very much for continuing your investigations. It's a difficult system for me to understand.
Regards,
Alan

bobbarry

Sorry to bring this back from the dead, but this is the best post on the CEC system I've seen yet

The link to the NCRS Rocky Mountain newsletter with the article is dead; so here is an alternate link:

https://manualzz.com/doc/6300991/pdf...crs---ncrs-rmc

ThumpingLotus7

Here is an update to that article -- a bit simpler and easier to follow.

https://docs.wixstatic.com/ugd/6daab...7c.pdf#page=26

firstgenaddict

71 is different than the 70 or 72.
I recently went through ops with CEC.
With 4 speed it does not operate in REV, only 3rd and 4th, with auto it works in rev and high gear.
With MY LT1, IF you push in the clutch with the shifter in 3rd or 4th the idle is kicked up to about 1200-.1300. move to first, second, or reverse the idle drops to 900.

71's use the temp switch in pass head if the coolant is above temp it kicks the engine idle up for better cooling.

Since KIRKCONNEL rebuilt my fan clutch my temp never gets much above 180 even sitting idling for 20 minutes in 90 degree weather.