1971 CEC Problem
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Safety Car
Joined: Sep 1999
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From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
1971 CEC Problem
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.
BTW, the CEC system has worked perfectly for the past 10 years.
Thanks in advance.
Last edited by gq82; Apr 24, 2015 at 01:37 PM.
Team Owner
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From: Crossville TN
The CEC temp switch in the R.H. cylinder head actually has 2 switches in it. One switch is to detect an operating temp TOO LOW; the other is to detect an operating temp TOO HIGH. In either instance, both switches are to turn OFF the ported vacuum feed to the distributor and return it to manifold vacuum. The two terminals on that switch body are actually wired together so that if EITHER of them are 'made', the CEC vacuum choice is bypassed to manifold vacuum.
The CEC system attempts to run the engine hotter at idle by retarding the ignition timing using 'ported' (or timed) vacuum (close to 0" Hg at idle) rather than manifold vacuum (around 16-20" Hg at idle). Hotter cylinder head temps means that more of the hydrocarbons are burned off. But, the engine can overheat if left at idle too long with the CEC system working. When it gets too hot, the "HOT" part of that switch trips and manifold vacuum is then fed to the distributor advance can, allowing the engine to cool off.
The CEC system attempts to run the engine hotter at idle by retarding the ignition timing using 'ported' (or timed) vacuum (close to 0" Hg at idle) rather than manifold vacuum (around 16-20" Hg at idle). Hotter cylinder head temps means that more of the hydrocarbons are burned off. But, the engine can overheat if left at idle too long with the CEC system working. When it gets too hot, the "HOT" part of that switch trips and manifold vacuum is then fed to the distributor advance can, allowing the engine to cool off.
Melting Slicks
Joined: Apr 2010
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From: Canberra Australia
2025 C3 of the Year Finalist - Modified
This may help.
I was not happy with ncrs article, did not answer all questions so we went further and My electrical engineer friend helped and we pulled all relays etc apart to check how they may really work in the circuit.
Possibly explains why the green pigtail is so long as well.
Covered here and in linked cf thread.
https://www.corvetteforum.com/forums...journey-2.html
I was not happy with ncrs article, did not answer all questions so we went further and My electrical engineer friend helped and we pulled all relays etc apart to check how they may really work in the circuit.
Possibly explains why the green pigtail is so long as well.
Covered here and in linked cf thread.
https://www.corvetteforum.com/forums...journey-2.html
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2018 Corvette of Year Finalist
2017 C3 of Year
The CEC solenoid attached to the carburetor is energized by either the engine temperature switch (cold override), time delay relay or a combination of the reversing relay and transmission switch.
So, you might be heading in the right direction with the temp switch.
Since you have already replaced the other items there is only the temp switch and the dreaded transmission switch which in your case is inside the tranny....On the manual trans switch there is a small PVC or plastic ball that wears and doesn't allow the switch to engage, not sure how the automatic switch works....
One other thing could be the wiring? I know you keep your car covered inside but is there a chance a mouse critter might have found a home?
I do recall there was an issue with the repo temp switches available, but can't remember the exactly problem? Perhaps the single prong vs. two prong switch???
You can test this by using another temp switch, by cooling and heating it while not installed in the head.
WB
So, you might be heading in the right direction with the temp switch.
Since you have already replaced the other items there is only the temp switch and the dreaded transmission switch which in your case is inside the tranny....On the manual trans switch there is a small PVC or plastic ball that wears and doesn't allow the switch to engage, not sure how the automatic switch works....One other thing could be the wiring? I know you keep your car covered inside but is there a chance a mouse critter might have found a home?
I do recall there was an issue with the repo temp switches available, but can't remember the exactly problem? Perhaps the single prong vs. two prong switch???
You can test this by using another temp switch, by cooling and heating it while not installed in the head.
WB
Thread Starter
Safety Car
Joined: Sep 1999
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From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Thanks guys for the added information.
Craig I did a search and came upon your diagram and your investigation into the infamous CEC system all of which was very helpful.
71vette & WB thanks for confirming how I thought the system works...again very helpful.
I was able to source a new thermal switch which hopefully will do the trick. I'm hoping it's not the trans switch
Once I get it on the lift I will be able to check the wiring....hadn't really thought about critters as I've never had an issue with them but anything is possible.
Anyway thanks again for the help, it's much appreciated.
Craig I did a search and came upon your diagram and your investigation into the infamous CEC system all of which was very helpful.
71vette & WB thanks for confirming how I thought the system works...again very helpful.
I was able to source a new thermal switch which hopefully will do the trick. I'm hoping it's not the trans switch
Once I get it on the lift I will be able to check the wiring....hadn't really thought about critters as I've never had an issue with them but anything is possible.
Anyway thanks again for the help, it's much appreciated.
Team Owner
Joined: Jan 2006
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From: Crossville TN
FWIW, I have left my CEC system pieces on the vehicle, but I normally swap vacuum lines so that the distributor gets manifold vacuum all of the time. At shows (if I choose to do it), I can simply move them over to 'stock' position and display the CEC system as it was from the factory.
The advantage of running with slightly less pollutants does not outweigh the potential wear/damage to the engine from running hotter at idle, IMO.
The advantage of running with slightly less pollutants does not outweigh the potential wear/damage to the engine from running hotter at idle, IMO.
Thread Starter
Safety Car
Joined: Sep 1999
Posts: 4,930
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From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
FWIW, I have left my CEC system pieces on the vehicle, but I normally swap vacuum lines so that the distributor gets manifold vacuum all of the time. At shows (if I choose to do it), I can simply move them over to 'stock' position and display the CEC system as it was from the factory.
The advantage of running with slightly less pollutants does not outweigh the potential wear/damage to the engine from running hotter at idle, IMO.
The advantage of running with slightly less pollutants does not outweigh the potential wear/damage to the engine from running hotter at idle, IMO.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Since my CEC system is not powered, I have a 'longer than needed' vacuum line from the distribrutor advance can to the end of the metal tube running from the carb solenoid switch. When driving it, I just pull that hose off the metal tube, remove the cap from the manifold vacuum fitting on the right side of the carb, and connect that hose to the fitting. The cap then goes over the end of the metal tube.
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Thread Starter
Safety Car
Joined: Sep 1999
Posts: 4,930
Likes: 11
From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Since my CEC system is not powered, I have a 'longer than needed' vacuum line from the distribrutor advance can to the end of the metal tube running from the carb solenoid switch. When driving it, I just pull that hose off the metal tube, remove the cap from the manifold vacuum fitting on the right side of the carb, and connect that hose to the fitting. The cap then goes over the end of the metal tube.
Team Owner
Joined: Jan 2006
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From: Crossville TN
Thread Starter
Safety Car
Joined: Sep 1999
Posts: 4,930
Likes: 11
From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Thread Starter
Safety Car
Joined: Sep 1999
Posts: 4,930
Likes: 11
From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Anyway I'm going to try to get the system to work the way it was designed...you know that NCRS thing but thanks for all the help, I appreciate it.
Last edited by gq82; Apr 30, 2015 at 08:54 PM.
Melting Slicks
Joined: Apr 2010
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From: Canberra Australia
2025 C3 of the Year Finalist - Modified
My 71 is an auto but when i got it it had its Quadrajet replaced at some stage with one from a chevy C10
7041211 CHEV 71 350 SERIES 10 TRUCK
It had the vacuum outlet as described through the choke
After I sourced a correct serial # carb for the auto it did not have the vacuum outlet.
7041212 CHEV 71 Vette 350 A/T
The manual should have .
7044210 CHEV 74 Vette 350 Hi Perf. A/T
All a little different :-)
7041211 CHEV 71 350 SERIES 10 TRUCK
It had the vacuum outlet as described through the choke
After I sourced a correct serial # carb for the auto it did not have the vacuum outlet.
7041212 CHEV 71 Vette 350 A/T
The manual should have .
7044210 CHEV 74 Vette 350 Hi Perf. A/T
All a little different :-)
Thread Starter
Safety Car
Joined: Sep 1999
Posts: 4,930
Likes: 11
From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
My 71 is an auto but when i got it it had its Quadrajet replaced at some stage with one from a chevy C10
7041211 CHEV 71 350 SERIES 10 TRUCK
It had the vacuum outlet as described through the choke
After I sourced a correct serial # carb for the auto it did not have the vacuum outlet.
7041212 CHEV 71 Vette 350 A/T
The manual should have .
7044210 CHEV 74 Vette 350 Hi Perf. A/T
All a little different :-)
7041211 CHEV 71 350 SERIES 10 TRUCK
It had the vacuum outlet as described through the choke
After I sourced a correct serial # carb for the auto it did not have the vacuum outlet.
7041212 CHEV 71 Vette 350 A/T
The manual should have .
7044210 CHEV 74 Vette 350 Hi Perf. A/T
All a little different :-)
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
An alternate source [for manifold vacuum] would be to put a "T" connector in the rubber line from the fitting on the intake manifold (behind the carb). Run the advance can hose to that "T" fitting for normal driving and cap off the hard line going to the CEC solenoid/switch. Move the dist hose over to the hard line and cap that 'extra' fitting on the manifold outlet for car shows.
Thread Starter
Safety Car
Joined: Sep 1999
Posts: 4,930
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From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
An alternate source [for manifold vacuum] would be to put a "T" connector in the rubber line from the fitting on the intake manifold (behind the carb). Run the advance can hose to that "T" fitting for normal driving and cap off the hard line going to the CEC solenoid/switch. Move the dist hose over to the hard line and cap that 'extra' fitting on the manifold outlet for car shows.
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2017 C3 of Year
Were you able to locate a correct temp switch? Another way to test the temp switch is to simply bypass it by looping the connector. Also, I have seen brand new defective time delay and reverse relays, right out of the box. Might want to test each part separately before throwing more parts and $$$ at it?
A properly functioning CEC system will not rob HP, but will help reduce harmful emissions. These early emission systems aren't all that difficult, I find them very interesting. Keep it original and working, my opinion!
Team Owner
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From: Westminster Maryland
Hi,
I agree with WB.
On a car as nice as GQ's I'd be disappointed if the CEC wasn't functioning.
I think the CEC system is sort of like the hidden wipers…. sweet mysteries when they don't work, but sorta cool when they do.
I can't tell you how many times I've shifted into 3rd and 4th while idling just to see if the rpm increases! Each time I think, "please, and then YES"!!!
Regards,
Alan
It's like a Thermos bottle… it keeps hot drinks hot and cold drinks cold…. but how does it know which to do?
I agree with WB.
On a car as nice as GQ's I'd be disappointed if the CEC wasn't functioning.
I think the CEC system is sort of like the hidden wipers…. sweet mysteries when they don't work, but sorta cool when they do.
I can't tell you how many times I've shifted into 3rd and 4th while idling just to see if the rpm increases! Each time I think, "please, and then YES"!!!
Regards,
Alan
It's like a Thermos bottle… it keeps hot drinks hot and cold drinks cold…. but how does it know which to do?
Thread Starter
Safety Car
Joined: Sep 1999
Posts: 4,930
Likes: 11
From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Update?
Were you able to locate a correct temp switch? Another way to test the temp switch is to simply bypass it by looping the connector. Also, I have seen brand new defective time delay and reverse relays, right out of the box. Might want to test each part separately before throwing more parts and $$$ at it?
A properly functioning CEC system will not rob HP, but will help reduce harmful emissions. These early emission systems aren't all that difficult, I find them very interesting. Keep it original and working, my opinion!
Were you able to locate a correct temp switch? Another way to test the temp switch is to simply bypass it by looping the connector. Also, I have seen brand new defective time delay and reverse relays, right out of the box. Might want to test each part separately before throwing more parts and $$$ at it?
A properly functioning CEC system will not rob HP, but will help reduce harmful emissions. These early emission systems aren't all that difficult, I find them very interesting. Keep it original and working, my opinion!
