mysterious vac line on firewall on jimmy...who can help

[01maroonz71]

it's on an 1984 jimmy w/ a 305/700r4/203. i've searched and some have said it's a TC lock up switch.....but the truck drives without it. it is broken clean off(nipple where vac line goes) so i plugged his vac hose with a golf tee for now and am trying to find a new switch.

it's on the pass side of the firewall and is almost right above the VC. it has wires running down out of it to somewhere, but i didn't have time to check where.

his (my fathers) truck is running like $hit and it bucks and tries to die once it hits like 40mph around 3rd gear. would this cause the converter to lock/unlock and cause these symptoms or am i chasing someting else?????

if so...does anyone know where i can get a new switch...gmpartsdirect.com and autozone don't have it.


oh yeah!!!! on the vac diagram by the radiator it says that's a :

TIP IN VAC SW....



thanks guys!!!
~Dave

 

[01maroonz71]

nobody knows eh?

 

[Blue85]

OK, on an '84 the "tip in" vacuum switch should be connected to the ESC unit to briefly retard timing for a quick drop in vacuum. This is to avoid knock. The wires from it should pass through the firewall to the ESC controller which is behind the glove box. I seriously think you can drive without it, assuming you plug the vacuum leak.

That being said, I do have a good one sitting here if you want to pay shipping + a few bucks...

The TC lockup switch is on the other side of the firewall, above the brake booster.

 

[01maroonz71]

cool man. ill tell my dad tomm when i see him. maybe this isn't related to it running badly. one thing my dad did notice was that under the hood smelled like gas like crazy, so i told him with these symptoms and such he should rebuild his quadrajet. hopefully that will fix it. thanks!

 

[dyeager535]

Is there another line to the switch?

Possible with one line connected, when the switch is "activated", a vacuum leak is created.

 

[broncoman6524]

if his truck is cutting out and sputtering at 40 mph this is either an electrical or fuel issue...if it was the tc not locking/unlocking properly it wouldnt really go any faster...the motor would run fien but the truck wouldnt move...if that was what yuo meant my bad, i took it as the motor would cut out...

check the fuel pressure...and wires etc.


oh and goodluck with that....i tried to find one a while back bc my dad though it was the kickdown switch for my th400... haha ah well. what yuo COULD do is get rid of the esc **** and get a standard 4pin module dist and be done. (with hei) then all you gotta do is hook up the vac advance, and the power into the dist and BAM like 5less wires. (thats what i did)

 

[Metrodps]

 

[nova]

I agree

 

[Blue85]

This is the switch I'm talking about. 1 vac line and a pair of terminals (Weather-pack 2-way).

When vacuum drops quickly, the contacts close.