TCS Trouble (Transmission Controlled Spark) - Pontiac GTO Forum
User Tag List

 
LinkBack Thread Tools Display Modes
post #1 of 4 (permalink) Old 05-05-2019, 03:36 PM Thread Starter
 
Herding Goats's Avatar
 
Join Date: Sep 2017
Location: CA
Posts: 20
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
TCS Trouble (Transmission Controlled Spark)

Hi All,
Working on my '70 4-speed car and having trouble getting the TCS system working. The system does seem well documented in the manual. The original M-21 was replaced with a '74 M-20 out of a Grand Prix. The '70 switch was bad so I purchased a replacement from an aftermarket parts supplier but it seems to operate backward of what it should. I have full vacuum advance in N,1st, 2nd, & 3rd and none in 4th. This, of course, causes the engine to race at idle. Is there a possibility that the interlock is different in '74? Does anyone know if the switch should be normally open or normally closed for a '70? My last question is if anyone that has eliminated this system would you recommend I do that. I really wanted to avoid modifying the original carburetor which does not have the appropriate vacuum provision, but given the trouble with the system perhaps now and in the future, it would be one less thing to break and potentially improve performance? Thanks in advance for any input.
Herding Goats is offline  
Sponsored Links
Advertisement
 
post #2 of 4 (permalink) Old 05-06-2019, 01:03 PM
64-67 Expert
 
geeteeohguy's Avatar
 
Join Date: Feb 2008
Location: Fresno, California
Posts: 8,457
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 98 Post(s)
The Transmission Controlled Spark was designed as a band aid to control NOx emissions at cruise. By retarding the timing at cruise. While this DID lower the NOx emissions, it also tended to lower fuel economy. I installed a ton of Echlin and STP kits 35-40 years ago when these cars were still in the CA smog program, and the kits eliminated ALL vacuum advance. They gave you a sticker to place on the dash not to exceed 55 mph. Those were the days. Reality today is you should have your car set-up as designed to be legal in CA on the streets. That said, nobody looking under the hood will know the difference. As a licensed Smog Check inspector/adjuster, I cannot recommend removing the part. I can tell you that the car will run better and get better fuel mileage with straight manifold vacuum advance and the switch bypassed. Your car, your choice. Glad mine are '65 and '67's and don't have any of this stuff on them!!!
geeteeohguy is offline  
post #3 of 4 (permalink) Old 05-07-2019, 12:24 PM Thread Starter
 
Herding Goats's Avatar
 
Join Date: Sep 2017
Location: CA
Posts: 20
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Hi Geeteeohguy, Thanks for the info and feedback. Regarding the elimination of the TCS system, for off-road use only, I believe I would need to find a different carb housing which would allow me to add a ported vacuum connection. Right now with the un-ported manifold vacuum at idle the engine races. I'll need to do some further research on this carb modification but would love to get the TCS system working properly until I can address that. For a system that is either on or off, this TCS sure has me baffled. My understanding of the early (1970) system is that the solenoid is default open and should be powered until the transmission is shifted into 4th gear, blocking all vacuum advance to the distributor from N-3rd. Then providing vac advance only in 4th gear (at cruise). I have verified that my solenoid, which I believe to be original, operates this way. For some reason, I am getting the opposite effect overall. Could the switch be defective? I have seen lots of problems with repro parts so that wouldn't surprise me. I can't imagine that the transmission (which has been changed) would have any internal changes that would cause the switch to operate in reverse? My original switch has failed and does not complete the circuit in any position so I cannot tell how it should work. Anything you see that I may be missing?
Herding Goats is offline  
 
post #4 of 4 (permalink) Old 05-07-2019, 04:43 PM
64-67 Expert
 
geeteeohguy's Avatar
 
Join Date: Feb 2008
Location: Fresno, California
Posts: 8,457
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 98 Post(s)
The switch could be reversed....any way to connect it differently? How many wires, etc.? As for the ported vacuum, most Pontiacs ran off of manifold vacuum. Some from the carb below the throttle plate, others from a hollow carburetor stud. You want to run manifold vacuum. And lower your idle speed to compensate. You will have a cooler running engine with better throttle response off idle. No need to change out the carb at all!!
geeteeohguy is offline  
Sponsored Links
Advertisement
 
Reply

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Pontiac GTO Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 2 (0 members and 2 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Vacuum Controlled Dashpot, Where to Buy One? Andrew69 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance 2 03-20-2018 06:38 AM
Remote controlled motorized hideaway license plate frame: $10 off plus free shipping! PFYC Exterior Discussions 0 02-08-2013 03:42 PM
Is clutch partially controlled by PCM? ISA2823 2004-2006 GTO General Discussion 3 05-31-2010 02:18 AM
05-06 remote controlled GOAT? GTO6 2004-2006 GTO General Discussion 3 08-18-2006 09:38 PM
Feeler: TCS Memory Module KPierson Interior Discussions 1 06-23-2006 04:05 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome