Project84

'86 GXL w/auto tranny. I labeled all the lines when I pulled the engine, but this one got wet when I washed the engine bay out, and I can't read the label. Its a metal tube and it comes from under the car, running along side the driver side of the tranny. It goes up to the top of the bellhousing where it has a rubber vaccuum line on it where it hooked to the engine. I'm assuming it went somewhere on the back side of one of the intakes or the back of the throttle body. Anyone know what this goes too? I checked the FSM and Haynes manual but nothing I could find directly references this line. I don't have all the emissions control stuff any more so I can't hook everything up and use the process of elimination cause I already eliminated a lot of ****. This is the only line I'm not sure of.

Thanks

hypntyz7

ar ou talking about 1) the vacuum lead frm the auto trans itself which went to the rear of the middle intake mani, or 2) the metal line on the frame from the gastank that goes to the charcoal canister?

sorry for the fubar typing, damn near just cut off my index finger...

Project84

not the one from the fuel tank. comes from the tranny itself

What is the middle intake? Middle of the lower intake?

hypntyz7

u call it upper intake prolly. where the cruise control would draw vacuum from, is where that hose goes. back pass side of intake; rear runner.

Project84

cool, thanks. once again you are the man. Since your here, what the hell does the auto tranny need vaccum from the engine for?

hypntyz7

all at's need to sense load/throttle position to figure out what gear to use. how do u think it knows when to kick down to pass, or shift at 3000 when you r cruisin and 6500 when u r at wot? some cars have a cable off the tb that leads to a valve...ours have a vacuum modulator that senses this.

hypntyz7

oh and i hope u r enjoying this info cause doing the 1 finger keybaord peck sucks ***...

Project84

never knew the vaccuum modulator was connected to the engine. I thought all that stuff was self contained in the tranny. So let me ask you this. Do all the little nipples all over the intake manifolds all suck in air? Are they all vaccuum sources or do some blow out air? I noticed that some lines go from the lower intake to the upper intake or throttle body. Is there a big pressure difference between the two? If its too much to explain then don't worry about it. I know its late.

Project84

sorry 'bout the finger dude.

White_Seven

I'm just glad it wasn't my engine you cut your finger on!

hypntyz7

actually it was, of all things. my ****** tow dolly. i got tired of replacing light bulbs so i got some new led lights. tryin to take off the old one, i was chiseling at a rusted, rounded bolt. the light is on a vertical "L" bar, and when i hit it the wrong way, my finger got caught between the top rough edge of the L and the 5lb sledge. cut my fukin nail in half

ok, you have to understand about vacuum abd atmosphere. air around us is atmos. when you crank the engine, it pulls air IN rapidly, because of it's design. Any internal comb. eng. is just an air pump.

Now think about the throttle body sitting up top. At idle, the plates are almost all the way closed. So you hve the block pulling air in, and the throttle plates stopping it from being pulled in. Air in front of the plates is still basically atmospheric, while air between the plates and the block (technically all the way to the rotor face) is vacuum, which is the lack of air pressure vs. atmospheric.

So, you have a hole (nipple) into the intake manifold between the plates and block, and you have a vacuum source. all the nipples on the intake are vacuum. there are a few special ones on the dynamic chamber that pull air from in front of thr throttle plates. This air supplies the OMP injectors and injector bleed sockets. Since there is a pressure difference betwen these 2 airflows, it is said to help atomize fuel better with these sockets. The oil injectord need the differential because vac. is pulling oil into the engine from underneath, and if there were vacuum pulling up as well, not much would flow. upplying non-vacuum air (still metered by the afm though) to them allows rhe oil to be sucked/siphon fed into the engine.