CEC system 71 LS-5

[Rick Garrett]

I am trying to reconstruct my cec system which had been removed for an aftermarket intake/carb setup.

am I correct in that 1.a vacuum line goes directly from carb to solenoid 2.solenoid vacuum line runs to vac advance on distributor

the wires or plug that went to the solenoid are gone, what harness did they come out of?

How is the wiring for the temp switch in the right hand head incorporated into this system. Is it part of the solenoid harness?

[Jack H.]

Re: CEC system 71 LS-5

#1 Vacuum line routing -- you are correct. Distributor vac advance runs to inside nipple on CEC solenoid. Outside nipple of CEC solenoid connects to carb vac source.

#2 CEC solenoid wires ran in a separate branch of engine harness routed along inside of LH valve cover. This branch contained two wires, was wide tape wrapped like other engine harness paths, and originated at the 'Y' on the firewall at/near/below the wiper motor.

#3 "How is wiring for temp switch in RH head incorporated?" Separate 1-wire harness to 2-terminal connector. Exits main firewall harness on RH side right behind RH cyl head and routes to temp switch in RH rear of cylinder head.

Troubleshooting a CEC system that's been 'cobbled up' is a neat task! This was a '71 Corvette only 'feature' and while the theory of operation is provided in the '71 CSM, there's narry a word on troubleshooting. You have to get the '72 CSM and follow the low performance Chevy V-8 cars where it appears GM 'dumped' their inventory of the short lived CEC.

Next, there are two control relays mounted on the RH side of the firewall. Littlefuse was the prime vendor. One is GM discontinued (time delay relay) while the other is still available from GM. But, what you get differs from original production in that the GM P/N is NOT on the can AND the original Littlefuse relays were date coded.....

These look to the novice like simple electro-mechanical relays. They are NOT! If you cut one open you'll find a Rube Goldberg hodgepodge of resistors, diodes, capacitors, and transistors hand soldered to various in-elegant mounting locations. Welcome to the archane world of DTL (diode, transistor logic). If you 'experiment' with these parts using simple battery/ground techniques to see how they open/close, you'll fry 'em into oblivion!!! Know what you're doing before you 'smoke' a correct dated vintage part....

since the '71 Chevy Chassis Service Manual provides a very nice description of each/every component of the CEC system in their chapter on

[Jack H.]

Re: CEC system 71 LS-5

#1 Vacuum line routing -- you are correct. Distributor vac advance runs to inside nipple on CEC solenoid. Outside nipple of CEC solenoid connects to carb vac source.

#2 CEC solenoid wires ran in a separate branch of engine harness routed along inside of LH valve cover. This branch contained two wires, was wide tape wrapped like other engine harness paths, and originated at the 'Y' on the firewall at/near/below the wiper motor.

#3 "How is wiring for temp switch in RH head incorporated?" Separate 1-wire harness to 2-terminal connector. Exits main firewall harness on RH side right behind RH cyl head and routes to temp switch in RH rear of cylinder head.

Troubleshooting a CEC system that's been 'cobbled up' is a neat task! This was a '71 Corvette only 'feature' and while the theory of operation is provided in the '71 CSM, there's narry a word on troubleshooting. You have to get the '72 CSM and follow the low performance Chevy V-8 cars where it appears GM 'dumped' their inventory of the short lived CEC.

Next, there are two control relays mounted on the RH side of the firewall. Littlefuse was the prime vendor. One is GM discontinued (time delay relay) while the other is still available from GM. But, what you get differs from original production in that the GM P/N is NOT on the can AND the original Littlefuse relays were date coded.....

These look to the novice like simple electro-mechanical relays. They are NOT! If you cut one open you'll find a Rube Goldberg hodgepodge of resistors, diodes, capacitors, and transistors hand soldered to various in-elegant mounting locations. Welcome to the archane world of DTL (diode, transistor logic). If you 'experiment' with these parts using simple battery/ground techniques to see how they open/close, you'll fry 'em into oblivion!!! Know what you're doing before you 'smoke' a correct dated vintage part....

since the '71 Chevy Chassis Service Manual provides a very nice description of each/every component of the CEC system in their chapter on

[Jerry Wallace]

Re: CEC system 71 LS-5

Hi Rick I sent an attachment directly to you that will show a wiring diagram for the 71 Corvette. This is off of an original Chevy Service News dated May of 1971. Hope this helps. -Jerry

[Jerry Wallace]

Re: CEC system 71 LS-5

Hi Rick I sent an attachment directly to you that will show a wiring diagram for the 71 Corvette. This is off of an original Chevy Service News dated May of 1971. Hope this helps. -Jerry

[Patrick H.]

Re: CEC system 71 LS-5

Rick,

The control solenoids that Jack was describing from Littlefuse are on the LEFT hand side of the firewall, not right (assuming you are in the car facing forward). They are mounted just inboard of the large mounting pad for the master cylinder/brake booster, and just outboard of the wiper motor.

Hope this helps.

Patrick Hulst

[Patrick H.]

Re: CEC system 71 LS-5

Rick,

The control solenoids that Jack was describing from Littlefuse are on the LEFT hand side of the firewall, not right (assuming you are in the car facing forward). They are mounted just inboard of the large mounting pad for the master cylinder/brake booster, and just outboard of the wiper motor.

Hope this helps.

Patrick Hulst