I will leave that disconnected. Definitely can't good et's at the strip with that. 
Automatic transmission spark control?????
Thread Starter
Instructor
Joined: Feb 2009
Posts: 141
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From: Greer SC
Automatic transmission spark control?????
http://www.ecklers.com/corvette-tran...1970-1974.html
Can someone please tell me the purpose of this???!!!
If I have this plugged up when I drive at the dragstrip my engine seems to stall out before ever reaching a good shifting RPM.(Cuts out about 3500-4000) Once I unplugged this I could shift all the way to 5500 RPM
Is this coincidental or is that what it's function is? If it's a freak thing at the time I unplugged it I also moved two plug wires that were somewhat close to my headers. They were touching to burn through just close.
Can someone please tell me the purpose of this???!!!
If I have this plugged up when I drive at the dragstrip my engine seems to stall out before ever reaching a good shifting RPM.(Cuts out about 3500-4000) Once I unplugged this I could shift all the way to 5500 RPM
Is this coincidental or is that what it's function is? If it's a freak thing at the time I unplugged it I also moved two plug wires that were somewhat close to my headers. They were touching to burn through just close.
Melting Slicks
Joined: Mar 2008
Posts: 2,023
Likes: 6
From: Austin Tx
The TCS system is an emmisions system. It's purpose was to retard timing by denying vacuum to the vacuum advance on the distributor.
The easiest way to bypass it, is to simply run the vacuum line from the vacuum advance directly to the carb. Most people with this system still installed do this, and when they are showing it, have the vacuum go thru the solenoid.
I think the purpose of the system, is to retard the timing to increase the engine heat to help with the burning off of emmisions. Intentionally retarding the timing, and increasing engine heat is not something we normally want, so on most cars it's been disabled/removed.
Other components of the system are, 1) the transmission switch (same as detent switch, so you want to keep that connected), 2) temp switch in passenger side head, 3) TCS vacuum solenoid, 4) a TCS relay behind the dash.
The easiest way to bypass it, is to simply run the vacuum line from the vacuum advance directly to the carb. Most people with this system still installed do this, and when they are showing it, have the vacuum go thru the solenoid.
I think the purpose of the system, is to retard the timing to increase the engine heat to help with the burning off of emmisions. Intentionally retarding the timing, and increasing engine heat is not something we normally want, so on most cars it's been disabled/removed.
Other components of the system are, 1) the transmission switch (same as detent switch, so you want to keep that connected), 2) temp switch in passenger side head, 3) TCS vacuum solenoid, 4) a TCS relay behind the dash.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
The trans switch is a pressure switch that only sees 3rd gear. That switch is also a good place for a major league trans leak..
And Mashman is correct- when it sees 3rd, the system cuts vacuum to the distributor and retards the timing- exactly why it falls on it's face at 3500 RPM.
And Mashman is correct- when it sees 3rd, the system cuts vacuum to the distributor and retards the timing- exactly why it falls on it's face at 3500 RPM.
Advanced
Joined: Jul 2011
Posts: 91
Likes: 6
Transmission control spark HELP
Hi all!
I just finished a full tune up on my '70 (timing, warm idle mixture and speed, points, condenser, plugs, etc) and the car was running GREAT except the fast idle was low. I decided to adjust the fast idle and in doing so something went drastically wrong.
I unplugged the lead to the transmission spark control, and then adjusted the idle screw (right side of carb). I put everything back together and now the motor will not advance past 3500 rpms with the secondaries open in third gear (I only tested it in third, it may or may not happen in other gears (rochester quadrajet). Based on this post it sounds like it is a problem with the transmission control spark. Am I missing something with the plug for the electrical lead to the TCS? Could unplugging and plugging it back in cause this malfunction? Or is this supposed to happen and was it just improperly plugged in before? Thanks,
Bob
I just finished a full tune up on my '70 (timing, warm idle mixture and speed, points, condenser, plugs, etc) and the car was running GREAT except the fast idle was low. I decided to adjust the fast idle and in doing so something went drastically wrong.
I unplugged the lead to the transmission spark control, and then adjusted the idle screw (right side of carb). I put everything back together and now the motor will not advance past 3500 rpms with the secondaries open in third gear (I only tested it in third, it may or may not happen in other gears (rochester quadrajet). Based on this post it sounds like it is a problem with the transmission control spark. Am I missing something with the plug for the electrical lead to the TCS? Could unplugging and plugging it back in cause this malfunction? Or is this supposed to happen and was it just improperly plugged in before? Thanks,
Bob
Advanced
Joined: Jul 2011
Posts: 91
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If not the TSC, do you have any thoughts on what could make it die at 3500 rpms in third gear (it revved to 4k in second gear, but wouldn't go past 3500 in third)?
Thank you very much!
Bob
Melting Slicks
Joined: Jul 2009
Posts: 3,264
Likes: 3
From: Vero Beach FL
Really? Maybe I'm way off then. What the heck did I disconnect? The service manual (for 69/70) does say that is has the TSC (this is a stick not an auto, not sure if that matters) and there is a mechanism in between the vacuum advance line on the distributor and the vacuum line to the carb.
If not the TSC, do you have any thoughts on what could make it die at 3500 rpms in third gear (it revved to 4k in second gear, but wouldn't go past 3500 in third)?
Thank you very much!
Bob
If not the TSC, do you have any thoughts on what could make it die at 3500 rpms in third gear (it revved to 4k in second gear, but wouldn't go past 3500 in third)?
Thank you very much!
Bob
I am sorry I am on the other side of the carburetor talking about the CEC solenoid. Some confusion on my part What I was talking about is listed on page 5 of the attached news letter.
http://ncrsrmc.org/Downloads/Mar-2006-Newsletter.pdf
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Drifting
Joined: Oct 2005
Posts: 1,615
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From: Forth Worth TX
A little confused on what you are doing/adjusting? Unless you know what you are doing and the symptoms for a bad TCS system (solenoid, switch, etc.) you are better off just removing the TCS system.
(In very broad general terms, when you are drag racing you would normally be at full throttle, so you won't have any vacuum advance anyway. You will be relying on your mechanical advance)
The TCS solenoid (on your manifold) only allows vacuum to the distributor in 3rd & 4th gear(based on engine temperature). By unplugging it electrically you won't have any vacuum going to the distributor vacuum advance can, ever.
You don't want to disconnect the TCS solenoid electrically and leave the vacuum lines in place. It's ok to leave the solenoid connected electrically, just remove(and plug) the TCS vacuum hoses and run a one piece vacuum hose straight from the carb to the distributor.
(In very broad general terms, when you are drag racing you would normally be at full throttle, so you won't have any vacuum advance anyway. You will be relying on your mechanical advance)
The TCS solenoid (on your manifold) only allows vacuum to the distributor in 3rd & 4th gear(based on engine temperature). By unplugging it electrically you won't have any vacuum going to the distributor vacuum advance can, ever.
You don't want to disconnect the TCS solenoid electrically and leave the vacuum lines in place. It's ok to leave the solenoid connected electrically, just remove(and plug) the TCS vacuum hoses and run a one piece vacuum hose straight from the carb to the distributor.
Last edited by Revi; Sep 23, 2013 at 01:07 PM.
Advanced
Joined: Jul 2011
Posts: 91
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Thanks Revi and Roco.
Revi let me give you some back ground and hopefully I can explain it better than before:
Long story short I tuned up the car, including timing. For a while it was out of time and would break up/back fire around 3500 rpm @ full throttle. This seemed fixed after timing it correctly. However, when I finished tuning the car the fast idle speed was incorrect - much too low. So I read up on adjusting the fast idle speed and the repair manual said that i had to disconnect the TCS lead to set the fast idle speed. I did so, and after adjusting the fast idle speed and reconnecting the TCS lead the car will not rev past 3500 rpm @ full throttle in third gear (secondaries open). Is there anyway the TCS malfunctioning can cause this or is it just coincidence that this happened after touching the TCS lead?
Thanks,
Bob
Revi let me give you some back ground and hopefully I can explain it better than before:
Long story short I tuned up the car, including timing. For a while it was out of time and would break up/back fire around 3500 rpm @ full throttle. This seemed fixed after timing it correctly. However, when I finished tuning the car the fast idle speed was incorrect - much too low. So I read up on adjusting the fast idle speed and the repair manual said that i had to disconnect the TCS lead to set the fast idle speed. I did so, and after adjusting the fast idle speed and reconnecting the TCS lead the car will not rev past 3500 rpm @ full throttle in third gear (secondaries open). Is there anyway the TCS malfunctioning can cause this or is it just coincidence that this happened after touching the TCS lead?
Thanks,
Bob
