wheatpj

What is Transmission/Temperature Controlled Spark (TCS)? I see it noted on the 1971 wire diagram and there are connectors on my new engine harness, but some of the plugs aren’t connected on my old wire harness. Other than a connector on the 4-speed, I don’t any TCS hardware on the engine. Would a LS5 have TCS?

7T1vette

I believe that the TCS system was only on the 'base' engines which did not get an A.I.R. pump. But, I could be mistaken on that. The TCS system was there ONLY for EPA emissions purpose. It did NOTHING for the engine, for economy, or for performance.

Basically, it retarded timing when the transmission (either manual or auto) was in lower ranges, but dropped out if the engine was either too hot or too cold and/or if WOT was employed. A retarded engine will run hotter in the combustion chamber and burn off more of the residual hydrocarbons.

Unless you just want to put your engine back into "factory-new condition" for shows or judging, save your time and money and leave it off the engine.

Alan 71

Hi wpj,
Yes, your LS-5 would have the system.
TCS was an emissions system used on 1970 and 1972 cars, while in 1971 the system used was named CEC.
The purpose of the system was to reduce emissions in the low forward gears
The reason you see the TCS note in 71 is because the electrical drawing in the 71 AIM wasn't updated for the new system. Instead separate information was sent to the dealers' service departments.
TCS stands for Transmission Controlled Spark while CEC stands for Combined Emissions Control.
The 1971 CEC system combined the throttle position and vacuum advance controls into one solenoid mounted on the right front of the carburetor.
In addition to the solenoid the system hardware consisted of:
a temperature controlled switch in the right side head,
a transmission gear sensor in the transmission,
a delay timer relay and a reversing relay, both mounted on the left side of the firewall,
and associated wiring in the engine harness.
The connectors you're seeing on your new harness are for these 5 components.
Regards,
Alan

wheatpj

Thanks 7T1Vette and Alan 71.

I guess what I find a little puzzling is how the retarding of the timing was accomplished. The breaker-point distributor on my LS5 is pretty simple. Was it done by dumping vacuum that would actuate the advance canister? At this moment, I can’t see how the circuit is plumbed in to accomplish a reduction in timing advance. It looks like the solenoid and the right side temperature control switch are AWOL. From a performance standpoint, it sounds like TCS or CEC is something I can do without. If I go without, are there any provisions that need to made.

Thanks again, Pat

Peterbuilt

http://www.73spot.com/index_stats_fi...ission/tcs.htm

Alan 71

Hi Pat,
The link from Peterbuilt is for the 70 and 72 TCS system.
The 71 CEC used a combined electrical/vacuum solenoid mounted on the front of the carb.
The sensor/switch in the right side head and sensor/switch in the transmission determined the operating conditions of the engine (temperature) and transmission (gear) and sent a signal to the solenoid to control idle rpm and vacuum advance based on those conditions
The reversing relay sends a signal to the solenoid to release the plunger in the solenoid to allow the idle to decrease, while the timing relay controlled the idle speed on restart of a warm engine.
Regards,
Alan

The CEC solenoid.


The hard and rubber vacuum line running back to the advance can on the distributor. (this is the source of the distributor's vacuum advance)



The reversing relay (forward) and the delay timer (rear).


Temperature sensor/switch.


Transmission sensor/switch. (Left side forward)

Peterbuilt

TCS is different from CEC.

7T1vette

These systems provided retarded timing by closing off the vacuum supply to the distributor advance can. No vacuum to can...no advance FROM that can. You then would only have mechanical advance for timing changes.

At idle, this could retard the spark several degrees. That makes an idling engine run hotter combustion chamber temps and burn more "rich" hydrocarbons from the charge.

When running in lower gears, same thing...no vacuum advance, only mechanical.

This system provided some benefit to emissions control; but NO benefit to mileage, engine life, or idle quality. The double-temp switch in the right cylinder bank was there to turn that system OFF if the engine was cold and warming up..AND turn it OFF if the engine was running TOO HOT (which it did if idling for very long). This was a cheap, quick add-on emission 'assisting' system that kept GM from having to re-engineer the engines for better emissions control or from adding more costly equipment to do the same thing, e.g. A.I.R. pump.

wheatpj

Alan, thanks for the photos and explanation of the CEC system. I have not seen detailed photos up till now. Photo # 2 really illustrates the system.

Your engine and engine bay is a thing beauty. I always enjoy seeing the photos and the information you post.

Thanks again

Pat

wheatpj

Thanks, that's good to hear. Since my system is AWOL, that is how I will continue.

7T1vette

Your engine and your wallet will thank you....