1971 CEC Question -- Help me to decode this testing procedure

[Billy S.]

Thanks in advance --


I am trying to fix my CEC solenoid which is always staying in the energized state.


The diagnosis flow chart in the yellow covered manual is pictured here:


Here are my reversing and delay relays:


Two questions:
1. Which is the purple wire it refers to in Step 2B Part 3? I know the revering relay is 842 (in the front), but I have no purple wire.
2. Which is the purple wire it refers to in Step 2C Part 3? I know the delay relay is 843 (in the back), but I have no purple wire.

[Mike E.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

In the Spring 2009 Corvette Restorer Jack Humphrey has an entire article devoted to this system, noting that faulty Chevrolet documentation and the fact that the May 1971 Chevrolet Service News has what is correct. If you need either of those, contact me, send me your email address, and I can scan those and get them to you.

[Billy S.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

Mike -- PM sent -- Thanks!

I have learned something new in my experimenting tonight... if I unplug the single unit plug from the delay relay (843, the relay in the back) the solenoid finally retracts. Of course it will not fire in this configuration though.... BUT if I ground the connector with the green wire (which fomes directly from 842) and the blue wire (I think this goes to the solenoid) it will fire -- and I can control the solenoid. I have a spare delay relay (843 littlefuse) and I tried it but it doesn't help. Does this give enough of a clue to someone whose a better electrical engineer than I??

[Terry M.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

Mike -- PM sent -- Thanks!

I have learned something new in my experimenting tonight... if I unplug the single unit plug from the delay relay (843, the relay in the back) the solenoid finally retracts. Of course it will not fire in this configuration though.... BUT if I ground the connector with the green wire (which fomes directly from 842) and the blue wire (I think this goes to the solenoid) it will fire -- and I can control the solenoid. I have a spare delay relay (843 littlefuse) and I tried it but it doesn't help. Does this give enough of a clue to someone whose a better electrical engineer than I??

Get the article Mike E refers to. The author, Jack H, IS an Electrical Engineer with a list of credentials that would knock your sox off. Have patience and follow what Jack says.

[Dave S.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

Get the article Mike E refers to. The author, Jack H, IS an Electrical Engineer with a list of credentials that would knock your sox off. Have patience and follow what Jack says.

Bill,
I have the Chevrolet Emission Control Systems Book for 1961-1972. I can scan or send the applicable pages to you. I also have Jack Humphrey's CD and write up also. Just need to find it. Let me know how I can assist.

[Billy S.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

Bill,
I have the Chevrolet Emission Control Systems Book for 1961-1972. I can scan or send the applicable pages to you. I also have Jack Humphrey's CD and write up also. Just need to find it. Let me know how I can assist.

I have the yellow cover book with the guy in the lab coat pointing. That is the one with the confusing diagnostic. What I need is Jack Humphrey's article. If you or Mike could e-mail that to me it would be great!

[Mike E.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

Attached is the correct wiring diagram. Bill, will send you the article next.
Mike

[Mike E.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

email won't send this for some reason--so here it is:

[Billy S.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

Thanks Mike & Dave!

[Billy S.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

Thank you all for your help and the articles. I figured it out!

Both my 842 and 843 were bad, as well as two spare 843's I had (although 1 of the spare 843s came from a box labeled broken, so I can't really blame that one!)

Now when I shift into 3rd and 4th the idle comes up, same for the first 15 seconds, and when the engine is cold. Boy what a thing!

[Mike E.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

Glad to hear it! Good job of persevering.

[Billy S.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

Hello -- Resurrecting my old thread to post an article I wrote which covers the full diagnosis and testing of this system. A "CEC" for dummies article if you will.

https://docs.wixstatic.com/ugd/6daab0_3288b3f124814924a99c509117a1df7c.pdf#page=26

[Mike E.]

Re: 1971 CEC Question -- Help me to decode this testing procedure

Great article!! Anyone trying to get a 71 right will benefit from this. Thanks for posting it!