roger3

1971 LS-5 454 has a temperature sensor on each head. Should both be connected? There aren't any wires for the one on the passenger side of the engine compartment.

...Roger...

The one on the pass side is the TCS sensor. Not needed unless you want the TCS to work.
Transmission Controlled Spark

roger3

What does the transmission controlled spark system do? Is it worth having?

CCrane65

It's an emission control system. It blocks vacuum advance except in certain cases such as third and fourth gear, the first thirty seconds after startup, temperature under 82 degrees or over 232 degrees and lastly WOT.

cc

roger3

my car has an automatic transmission so I guess it shouldn't have came with TCS? Is that right?

70Donnybrooke

The automatics had it too. My 70 does.

roger3

I just bought this car 2 weeks ago and don't know much about it's history. I bought it from a used car dealer who got it on a trade in.

When I drive it in traffic the temperature slowly climbs above 220F. Would this TCS system do enough to keep it from overheating?

When I bought the car it was running very rough (sputtering and backfiring through the carb during acceleration). I checked the timing and points dwell a couple of days ago and found both of them way out of adjustment. I haven't driven the car in any traffic yet so mabye it will not run hot anymore.

CCrane65

The idea behind the TCS system is to raise the combustion chamber temperature enough to burn off more hydrocarbons so yes, it does raise the temperature of the engine. But, it doesn't sound like yours is connected completely if you don't have a wire on the passenger side temperature switch.

There should be a green jumper wire that connects to a harness connector against the firewall behind the right head. On my '72, the wire from the harness is blue. The switch tells the TCS system when the engine temp is over 82 and under 232. Most of the parts vendors sell the jumper wire.

The TCS has no part in keeping the engine from overheating but I would make sure the cooling system is in good working order.

cc

BTW, I would make a decision to either connect the TCS system properly or bypass it completely. To bypass it disconnect the hose from the vacuum advance can on the distributor and run a new hose from there to a manifold vacuum port on the carburetor. Then disconnect the hose that runs from the carburetor to the CEC solenoid and cap the carburetor port.

Do not disconnect the electrical connector on the CEC solenoid as it has nothing to do with the TCS. It powers the idle stop (anti-dieseling) part of the CEC.

roger3

Right now my car doesn't have the TSC solenoid nor idle solenoid. It has an aftermarket edelbrock carb so the air cleaner doesn't fit well. I am going to put the original quadrajet back on it and am trying to determine what else I should or might want to install. I am not going to enter it into any car shows or anything but I do like to keep things original.

Should my car have both a TSC solenoid and idle solenoid? I have wires laying on top of the intake manifold on the drivers side with an end connector shaped like an "L". There ar no wires connected to the temperature sensor on the passenger side of car.

CCrane65

The CEC is a combined TCS and idle stop solenoid. It has a bracket that attaches to the front corner of the Q-jet. Your wire laying on the intake will connect to the end of it. It also has vacuum ports on it, one pointing straight up and one pointing straight out. The one on top has a hose that goes to the vacuum advance can. The other port goes to a ported vacuum source on the upper right front corner of the carburetor.

LS5 engines, as with most big blocks, run very hot and are prone to dieseling so I would definitely use the idle stop part. Maybe just run the hoses and leave them laying loose for the TCS. That way it looks stock but runs cooler and better because vacuum advance is available at all times.

If you have a Chevrolet Chassis Service Manual for your car, it has the specific method for setting the minimum idle speed with the idle stop solenoid.

cc

thoyer

The solenoid does not perform an anti-dieseling function. It is there to increase the idle speed under certain conditions to make the engine burn cleaner. Once the ignition is turned off, so is the solenoid. Also, do not use the solenoid to set the idle, there is a procedure that involves disengaging the solenoid to set the curb idle (idle speed screw on carb), then engaging the solenoid to set the CEC system idle.

This article provides some very good information on the 1971 CEC operation.

http://ncrsrmc.org/Downloads/Mar-2006-Newsletter.pdf

Tom

roger3

All of the wiring is in my car so I'm going to hook it up and see how it goes.

I need to buy the solenoid and bracket. Dr. Rebuild has these parts brand new, original Delco items.

My distributor still has points. I plan on replacing them with an electronic ignition conversion kit (same distributor). Will this be a problem with the CEC/TSC?

CCrane65

Tom, I don't know what the 1971 Chevrolet Chassis Service Manual says about setting the minimum and curb idle speeds but in the '72 manual it says to disconnect the idle stop solenoid then, using the minimum idle screw, set the minimum idle speed to 400 rpm or the lowest speed the engine will continue to run at.

Then it says to re-connect the solenoid and use the plunger to set the curb idle speed to 750 rpm (for a manual transmission).

And yes, it does stop dieseling by ensuring the throttle plates are completely closed when the engine is shut off.

The author of the NCRS article does not explain the "idle solenoid" completely because it is in fact an anti-dieseling device. He does however say that the '71 and '72 systems work essentially the same.

Well, I'm here to tell you on the '72 the idle stop solenoid energizes once when the key is turned to the run position and de-energizes when the key is turned off and it never cycles between on and off while you are driving under different conditions.

Yes, the idle speed does modulate as described in the NCRS article but it is because of the TCS solenoid cycling between blocking and passing of vacuum advance.

cc

CCrane65

Not as long as it retains vacuum advance. HEI is just a different method, albeit a much more accurate method, of delivering the spark to the plug wire.

cc

roger3

Thanks everyone for the information. The level of detail you guys provide is incredible and very much appreciated. I will order the parts tomorrow and put them on the car in the next couple of weeks and let you know how it works out.

Thanks again!

Roger

thoyer

Agreed. I went back and read some info last night to refresh what is left of my memory.

The only part missing from my system was the solenoid. I was able to find an original one in very good shape this summer and planned on putting it on and getting the system working. I figured that since the rest of my car is bone stock, I should have a working CEC system. Well, to be honest, I bought a C6 back in June and promptly lost the motivation to work on the CEC system on the 71. I'll make it a spring project...............

Tom