Vac Advance to Pass Emissions

[Devin]

I have been trying to pass emssions here in Denver. It has failed several times due to high CO. I took the tercel to a free state run evaluation and it passed there (which doesn't count) but he said that it was running rich at high RPMs and the high altitude valve was stuck in one position. Well I noticed last night while checking the timing that the vac advance might not be working because it shows 5 BTDC with or without the hose pluged. (Is there a way to check for sure?) Will putting a new vac advance help lean out the mixture at high rpms? If I were to get one from a junk yard what do I need to replace? Just that canister below the distrubutor with three ports or is there more to it? Also, high altitude valve? What does that do? Swap it with a junk yard one?

Thanks guys! One day I swear, I will answer a question on here instead of asking all the time.

[Highlander]

Hey Devin,
The HAC (High Altitude Compensator), as its referred to, "adds air to the primary low and high-speed circuits and also advances the ignition timing to improve driveability at high altitude above 1198m" basically it allows additional air to flow into the carb leaning out the mixture (See page EC-40 in the FSM)
I have an extra sitting on the junker if you need it, it may be malfunctioning due to the broken diaphragm in the dizzy. You might check the filter on the bottom of it, if its clogged up, it won't bleed any air into the carb either. There is a check-out procedure on page EC-41.
Let me know if its faulty, and I can supply you with another HAC.
The vacuum advance can be removed just by itself from the dizzy. a couple of screws and one dammit clip if I remember, nothing else. They are available aftermarket, most of mine are dead anyway.
Mine have made it through emissions for years without either vac advance or a 'working' cat-didn't know it until recently though.
I'm assuming that you took it to the Teller St station? There's a guy who works for the state (maybe that's who you're referring to) by the name of Joe Levonas who will run the car on his dyno at the teller station and help you to pass (won't do anything illegal either) If you need to make an appt with him his # is 303-404-0265- Its free.
Nice guy, used him a few times.

[Devin]

Thanks Mark,
I checked and it does appear my HAC is working now. It has pretty good suction. Though still the vac advance is not working. I am planning on going to the junkyard soon anyway, is there anyway to check if the vac advance canister is good without putting on a running car? Also do you think a fuel additive would help?
I went to the emissions place on 2nd and Bryant, they were actually fairly rude, but that was to be expected. If I can't get her going I will call your guy, for sure. Thanks for the help.

[john]

Good Morning Devin,
I've noticed when checking my Tercel's timing that it doesn't matter if I plug the vacuum line to the distributor or not. It still reads the same. You can check the advance if you rev the engine while looking at the timing marks with your timing light. Check to see if the marks move when the engine is reved. If they move, the advance is fine, I think.

I just got my tercel through smog check with lots of help from members of this forum. It had the highest CO and HC readings the smog shop had seen. It is now the cleanest they have seen.

Here is what I did:

replaced plugs, wires, rotor and cap (this actually made the next smog check even worse).

Took members advice and checked the AAP valve. It is located on the passenger side, front lower corner of the carb. It is dome shaped and has a vaccum hose attatched. Disconect the hose and see if there is gas in it. If there is gas in the vacuum hose it will get dumped into the manifold and cause a too rich condition, which will also probably ruin the cat. I had not even heard of an AAP valve a couple weeks ago. It has a membrane in it which will rupture over time. Easy to replace. hope this helps, john

[Highlander]

Devin- you can check the vac advance by using a small piece of (clean) vacuum line and sucking on it, if the diaphragm arm (the attachment that goes inside the dizzy) moves, its fine. The other alternative is to use a small hand vacuum pump that they usually sell to help you bleed the brakes- with those you can also see if it holds the vacuum or just leaks slowly. Horrible freight sells some for ~$15 I think.
John- You're looking at centrifugal advance, if you are watching the timing mark and apply a vacuum to the vac advance line (see above- use a clean line), THEN you should see it advance. The centrifugal and vacuum together get you the advance that you need when you need it. If you disconnect the vac lines and rev the engine and the timing doesn't change, then your centrifugal weights are locked up and you're in worse shape (timing-wise) than if the vac advance doesn't. But you're right about the AAP- That's often times the cause of over rich no matter what, When the diaphragm breaks, the vacuum form the engine just sucks fuel in through the TVSV lines. If you disconnect the AAP vac line and there's fuel in it, there's your problem.

[takza]

I have been trying to pass emssions here in Denver. It has failed several times due to high CO. I took the tercel to a free state run evaluation and it passed there (which doesn't count) but he said that it was running rich at high RPMs and the high altitude valve was stuck in one position. Well I noticed last night while checking the timing that the vac advance might not be working because it shows 5 BTDC with or without the hose pluged. (Is there a way to check for sure?) Will putting a new vac advance help lean out the mixture at high rpms? If I were to get one from a junk yard what do I need to replace? Just that canister below the distrubutor with three ports or is there more to it? Also, high altitude valve? What does that do? Swap it with a junk yard one?

Thanks guys! One day I swear, I will answer a question on here instead of asking all the time.

If you do a Google search for Tercel emissions or ????......there is a page specific to issues of getting the Tercel to qualify for emissions testing...with some details and stats on what was typically needed.

[Petros]

the vacuum advance will not make you fail emissions, it only helps fuel economy. More advance actually raises the emissions slightly, it will not harm emissions if it is failed, unless it the diaphragm is so badly ruptured it acts like a large vacuum lean (just plug the line off if that is the case). You should verify if the mechanical advance is working, just watch the timing mark when you rev the engine with the timing light on it, it should advance.

Many of the vac advances in the wrecking yard will also be bad, but I find it an easy check to just suck hard on the line and see if the arm moves. If it is ruptures you will just suck air through it. either clean up or replace the altitude compensator, that is likely where the problem is.

[Devin]

Confounding new development:
I went to the junk yard for a used vac advance figuiring I only needed it to work for a little while to pass the test. Well out of the three there , one appeared to be good ( upon suction the arm pulled in). So I put it on and hooked up the hoses and the timing was way off. It was off the scale. So I set the timing as shown by Keith in a write up. https://tercel4wd.com/forums/viewtopic.php?f=7& ... ing#p38293 . So with everything plugged the timing showed 5 BTDC but with the vac advance hooked up it was way too high (above 20). So I figured, oh well, I have another bad vac advance and plugged up the hoses and varified the 5 degree timing and resolved to take the test the next day. Well this morning I drove around on the highway for about 20 minutes and pulled into the emissions parking lot and checked to see it the HAC valve was working, which it was not. But, I guess that makes sense because I had plugged up the line to the vac avance. So I unplugged it and the HAC was getting suction. Perfect! But then I check the timing to find it way high again, and more puzzleing, with it replugged up it was around 10. How can this be if yesterday it was a perfect 5? Can timing change like that? Also I need some opinions on how to plug the vac advance and still have the HAC work to get me past emissions. I am utterly confused! Thanks, and sorry for the long post.

[dlb]

it sounds like you had the two vac lines from the vac advance canister mixed up. the lower port of the vac can should go to ported vacuum and the upper port should go to manifold vacuum. if set to stock 5* BTDC and vac advance hooked up correctly, it should idle at about 13* BTDC @ 950 rpm. if you have the lines mixed up it will idle around 24* BTDC. there should be a vacuum diagram on the underside of your hood that you can follow to correctly route any vacuum lines.

if you set the timing w/ no vac advance to 5* BTDC but later found it to be at 10* BTDC, also with no vac advance, i wonder if the revs were consistent between the two readings. when setting the timing, the idle should be about 950 rpm. if the idle is higher or lower it will affect the degree of mechanical advance so that could be the cause of the apparent change in timing, or it could be a vacuum leak. check for cracked or disconnected hoses--maybe you accidentally pulled one off while hooking up the other stuff.

[Devin]

I am pretty sure I had them hooked up correctly. I even have it memorised. The port closest the drivers side sidewall has a filter on it and goes forward toward the bumper. The one next to it goes behind the engine to the HAC. The bottom port goes to forward also but with no filter. Isn't that right? But if I set the timing for sure using Keith's method, can it change? Becuase I could have sworn the RPM were consistent.

[Petros]

your mechanical could be hanging up, not unusual. take the dist cap off and spray inside (under the backing place) with LPS or CRC, PB Blaster or similar. wiggle the rotor back and forth to verify smooth operation. If it still hangs up it should be taken apart and the gunk and corrosion cleaned out of the mechanism.

[Devin]

Well, I put the timing right (5 degrees BTDC), bypassed the malfunctioning vac advance, made sure the mechanical advance was working, and made sure the HAC was working... and I still failed. There was no drop in CO. Now I am wondering if I can put a new catalytic converter on to cure my CO woes. Is this a sound next step? Thanks

[john]

Hi Devin,

When I changed my cat, here is how it affected my Tercel's emissions.

It lowered the HC's and NOX to almost 0.

In 2009, changing the cat actually increased my CO from .06 to .22 (under load at 25mph).

2 weeks ago, changing my cat again took my CO from 3.7 to .71 (I passed smog). Once again, HC and NOX went to about 0.

Replacing my AAP valve and cleaning EGR brought the CO down from 6.1 to 3.7.

Other sources of high CO: dirty air filter, faulty oxygen sensor, low engine temp.

If you do replace the cat, go directly to the smog shop afterwards. They easily lose their effectivness if the car is not tuned perfectly.

Best of luck, john

[Highlander]

Devin- something else about a Cat is that you need to get the engine warmed up before you get to the emissions station. The catalyst has to be firing to be effective, so make sure that the car isn't cold when you get there (even though you sit for a while). My brother used to advocate a quick drive on the turnpike before the emissions station.
Regarding the vac advance, I have to agree that it sounds like you've got it tapped into manifold vacuum rather than throttle plate vacuum. The difference is that the manifold will have high vac at idle and low vac at full throttle, and vice versa. Since you're seeing high advance at idle which goes away when you unplug the advance line, it indicates the vacuum being applied at idle, which there should be little or none of. If you hook it up and then rev the engine, does the timing come back down? if so, that would be definitive that you've got manifold vacuum where you should have throttle plate vacuum. check the TVSV connections and follow the color coded vac diagram that Tom (ARCHINSTL) made up (in Repair Guides) also check that the hard lines are connected correctly on both ends.