Vacuum advance

Lollypop · Post by **Lollypop** » Mon Dec 18, 2006 11:37 pm

Somebody please answer a question for me.

On the vacuum advancer there are three ports. Two on the top (closest to the IIA) and one on the bottom (out on the end). what do all three do individualy? Which ones need to be hooked up for the advbance to work properly?

ever since I did that work awhile back my timing has been screwy, just not right but Im not sure what I have plugged wrong or not plugged etc. Ive lost my 4AC UMPPPP and I want it back.

=====Justin=====

Mac · Post by **Mac** » Tue Dec 19, 2006 2:58 am

you can download the FSM from the main page of tercel4wd (64MB .pdf file) and it will tell you.

i'll see if i can take some pictures of my terc's vacuum system, but i'm not sure when i'll be picking it up (had to leave it parked after a christmass party).

but which part are you curious about, i'm guessing your talking about the valve for controlling the EGR on the RH (pass) side of the engine?

Post by **ARCHINSTL** » Tue Dec 19, 2006 3:51 am

The tube on the bottom is connected directly to the EGR valve modulator and carburetor and indirectly to the EGR valve, the EGR valve modulator and the second port from the top of the TVSV.
The rear top tube is connected to the HAC valve.
The front top tube is connected to the valve on the intake manifold/vacuum source (which latter's other tube goes to the third from the top of the TVSV).

Check the color tubing diagram that AbusedJalopy posted in the Repair Guides section back in 2005 - very helpful.

I actually have the HAC tube blocked, as STL ain't too far above sea level, and neither are you.
Tom M.

2wagons · Post by **2wagons** » Tue Dec 19, 2006 12:48 pm

Check that all three ports will hold vacuum. If one leaks, your vacuum system will leak and your timing may be off.

Lollypop · Post by **Lollypop** » Tue Dec 19, 2006 10:08 pm

OK well the FSM didnt tell me much....I read it all and no answer. The colored pic of the vac routing did shed a little light though. Only thing is my motor has nothing but a weber carb. NO smog mess at all, NO EGR, NO vacuum except for the carb.

Best I can tell.....the bottom port goes to the EGR Vac Mod.....the top one on the drivers side goes to the little vac source on the manifold.....the top one on the passenger side goes to the HAC.

SOOOOOO....I have NO EGR---dont need the port on the distr. so plug it
I low altitude-----Dont need that port on the distr. so plug it

That leaves me with one port on the distr. for advance so theres my problem fixed and if I still have problems with timing then the advance in the distr. itself or the vac cannister is malfunctioning......

What-chall-think?

=====Justin=====

Lollypop · Post by **Lollypop** » Tue Dec 19, 2006 10:36 pm

OK after more indepth lookin and thinking (which is kinda hard sometimes) I have found myself to be wrong.

I studied the HAC page in the FSM and referenced back to the color photo and found out that the two ports on the dist. on top are both part of the HAC (which I dont need) and the bottom port is the vac advance WHICH AINT EVEN HOOKED UP ON MY CAR Soooo when I do pull a vacuum Im changing the timing to who-knows-what. Another thing is that I have the two top ports, one going to the carb and one going to the gas filter which is not a vac source as I had thought before it is allowing vacuum God-knows-when so I have had the whole thing screwy So theres the skinny ....anyone who has removed the smog crap just pipe the bottom port and away we go.

=====Justin=====

Post by **ARCHINSTL** » Wed Dec 20, 2006 12:42 am

Huh -
I thought the valve/thingie on the intake manifold was the source of vacuum for various items.
So it is a gas filter? It filters - what?
Tom M.

Lollypop · Post by **Lollypop** » Wed Dec 20, 2006 12:55 am

The FSM calls it a gas filter and explains in another spot how it works and the purpose. something along the lines of it opens at a certain telp...tomorrow when its not 1:54 in the A.M I will find it and "splain" it all....
night

=====Justin=====

Jts · Post by **Jts** » Wed Dec 20, 2006 11:53 am

The gas filter is a source of vacuum. It supplies vac to alot of the major components. I believe its purpose is to not allow gas into the vac lines, not that gas would really travel up the airstream. The gas filter should be connected to the vacuum advance canister. The most bottom nipple on the can is the secondary vacuum source. Thats the one you leave plugged in while timing. The middle nipple is the main advance source and is the hose you pull off and plug while checking timing. Pull this hose and feel if you have strong vacuum idle. It should suck pretty hard at idle. The 3rd nipple is the high altitude system, and is the one that has a restricted nipple. If you look closely, its like a jet. You might have to take the can off to see it.

Lollypop · Post by **Lollypop** » Thu Dec 21, 2006 9:02 pm

Well Jts....Maybe I'm reading the FSM wrong but what I read is.

As far as the gas valve goes one prt supplies runs over to the TVSV the other prt runns over to one of the top prts on the distributor which is part of the High Altitude Compensation system (p. EC-40).

As far as the distributor goes the other top port on the dist. runs over to the HAC valve which is still part of the High Altitude Comp. system therefore, the TWO top ports are part of the HAC so that only leaves one, the bottom one, which runs over to the carb. and teeing to the EGR vacuum Modulator.

Now from what I understand the vacuum advance is for low rpms then the centrifigal advance kicks in.

Whith all that said..... my research tells me that the bottom port is the vac advance and the best place to put it would be straight to the Weber or whatever carb ya have.

=====Justin=====

2wagons · Post by **2wagons** » Fri Dec 22, 2006 11:03 am

Lollypop,
I think you are right. As i recall the top two lines are to the HAC and work together to supplement vacuum advance depending on ambient air pressure (ambient air pressure is determined by the diaphragm in the HAC). I think ones pulls and the other will release timing to reach correct advance. IÃ¢â‚¬â„¢ll look at mine tonight and let you know how mine is connected.
My secondary advance is leaking and I have just plugged the lines (top two lines). After i plugged them, the idle settled down and the engine ran much better. The leaking secondary advance was apparently causing a leak in the vacuum system.

Jts · Post by **Jts** » Fri Dec 22, 2006 4:07 pm

The vac advance works on light load/high vacuum situations. It will advance the timing when you are lightly on the gas. Floor it and the vac advance retards back to its initial position. Thats the general workings of a vac advance

I believe the 2 hoses that go to the vac advance are a manifold vac line and a pre carb vac line. These 2 different sources of vacuum do not always correspond to the same level of suction. The distrubutor uses the 2 sources to determine how much advance to give.

Either way, the hose that goes to the middle portion of the vac can should cause the advance to go from 5 to 13 degrees like the FSM says. Does it do this for you?

Lollypop · Post by **Lollypop** » Fri Dec 22, 2006 5:50 pm

Well I'm not sure what degree it goes up to with the vac adv. I do stand by my previous post as to how it all works.

Even if, by some chance, I'm wrong there is one thing I do know for SURE. I woke up this morning strolled out to Myrtle and plugged both top vac ports on the dist.(HAC prts), plugged both ports on the gas filter, ran a vac hose from the bottom most port on the dist to the Weber carb sitting there looking all purdy, took it for a test run and BA BAMMMMM my 4AC came back to its former "ass haulin' " self. NO BOG AT ALL in any gear spin wheels all the way through 1st and part of 2nd then all the way up to 90 something (skeered to look down at the speedo at that point)

So even if my FSM research and conclusion are wrong.....I'm leavin it just the way it is.....hell if it got any better Myrtle would sprout wings and fly away.

=====Justin=====