72 LT1 Spark Control Solenoid

[Joe S.]

A: Could someone tell me the function of this gizmo and how it works?
B: Could someone also tell me besides the vacuum advance, what else is connected to it. Looks like two connections on one end and one connection on the other. The AIM is not exactly clear where things are going.

When I bought the car a few years ago there was a replacement carb and distributor and no solenoid (although the originals were included with the car). I've rebuilt the originals and am putting them on along with a solenoid. Just need to connect the dots.

The electrical connector is still there so that's no problem.

Thanks

[Patrick H.]

Re: 72 LT1 Spark Control Solenoid

Joe,

See my 72 L-48 below.
Same idea. The connections will be the same. For the vacuum hose layout, see Dr. Rebuild's catalog. The front goes to the carb, the side goes to the distributor. I cut my own piece of foam for the back port from a generic piece obtained at AutoZone near the air filters, etc.

Patrick

[Gary Schisler]

Re: 72 LT1 Spark Control Solenoid

In addition to what Patrick says about the orientation of the hoses, the 72 GM Service Manual gives a good description of the function of the solenoid - when it opens and when it closes. The manual also gives a good description of troubleshooting.

Gary

[Patrick H.]

Re: 72 LT1 Spark Control Solenoid

...and thanks to Gary for previously teaching me how to troubleshoot the system and get old, crusty solenoids working again.

Patrick

[Lyle24961]

Re: 72 LT1 Spark Control Solenoid

I have noticed on some of the TCS solenoids they have a extra white plastic shield to hold the foam filter. This is usally found on LT-1s and big blocks and I have found no pattern for its use. If you have a 4 speed at warm idle put it in 4th gear and with a delay of up to 30 seconds your idle should increase showing this part of the system is working. I would like to know a test for automatics.

Lyle

[Terry M.]

Re: 72 LT1 Spark Control Solenoid

Lyle,
The TCS test for M40 is to place the transmission gear selector in reverse. The idle should try to increase. One can usually notice the rear of the car raise up as the increased engine RPMs are restrained by the brakes. It is a little less certain test than the one for 4-speeds, but is no problem to detect.

[Gary Schisler]

and if 30 seconds isn't enough

wait anothe 30 seconds. My 72 LT1 TCS system takes 45 seconds +/- to come on. I am relying on memory here, but isn't there a test for all of the functions of the TCS system (including the auto trans) in the 72 GM Service Manual? I thought the emissions section gave a complete breakdown of "how" and "when" plus a diagnostic. I will look this up later if someone needs it.

Gary

[Lyle24961]

Re: and if 30 seconds isn't enough

The how and when chart is fine for fixing the system. In ops or a PV a method that is short and sweet is better. The timer on your LT-1 must be set longer than most or has a contact problem.
Lyle

[Gary Schisler]

Re: and if 30 seconds isn't enough

Lyle, my car has been Top Flighted locally and regionally and the time for the TCS has not come up. I can't recall what the judging manual says but I am just going from a data base of one.

Gary

[Dick W.]

Re: and if 30 seconds isn't enough

Gary, just wait until you PV. Guaranteeeee that it will be checked. Should be done in ops also.

[Gary Schisler]

Re: and if 30 seconds isn't enough

Actually, I misspoke (mis-typed?). Yes the TCS was checked during the ops portion. Got a "Hmmm" when 30 seconds elapsed and a grin with a thumbs up when the TCS kicked on. Again, I am relying on memory from the Atlanta Regional four years ago. I picked up a spare TCS relay but its location tells me that this is for a really drastic failure mode before I even begin to worry about replacing it. I can live with a 45 second TCS mode.

Gary