Fails emissions test - CO too high

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Rickety Rhino
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Fails emissions test - CO too high

Post by Rickety Rhino »

Does anyone have ideas what else I can do to lower CO so I can pass emissions?
The emissions test shows CO GPM at 40, and the limit is 30. Two years ago it passed at 24.8 GPM.
The HC, CO2 and NOx are all well within limits, same as 2 years ago.
Here's what I've done: adjusted valves, fast idle, TP, checked float level (exactly in the middle of the sight glass),
PCV valve, new oil & filter, new air filter. The distributor vacuum advance leaks, so I plugged
a vacuum line 2 years ago and it passed emissions then. The timing is set at 10 deg BTDC
to compensate for this. I tightened some, but not all of the oil pan bolts, because they seemed loose,
but maybe the engine isn't sealed completely.
Thanks for any advice!
Location: Boulder, Colorado
Smokey The Brake - 1984 4WD, 230K
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Petros
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Re: Fails emissions test - CO too high

Post by Petros »

reset your spark timing to 5 deg BTDC, and than retest. I think that should do it. afterwards make sure to set it back to 10 deg, or you risk damaging the exhaust valves. you might also replace your spark plugs if they have not already been replaced recently. put the correct heat range in per the FSM.

I do not think anything else you did will affect the CO. CO forms with a hotter combustion temperatures, the higher advance allows for that (and improves fuel economy and efficiency because of it), but will increase the CO production.

good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
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Rickety Rhino
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Re: Fails emissions test - CO too high

Post by Rickety Rhino »

It failed again, with almost the same value for CO. It has new NGK BPR5EY-11 spark plugs, timing is at 5 deg BTDC. I also put in a new distributor rotor and O2 sensor. Last time the emissions tech said it was running too rich. I checked the choke, it's vertical when the engine is warmed up. The center post on each of of the old spark plugs was grey to cream colored, with no deposits. The outer ring around the post was black, and not oily. I'm not sure where to look next - any ideas?
Location: Boulder, Colorado
Smokey The Brake - 1984 4WD, 230K
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Petros
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Re: Fails emissions test - CO too high

Post by Petros »

too rich?

have you checked the AAP? pull off the vac line to it and see if there is fuel in it. if so you can cap off both ends and you should pass. you only need that for cold start to prevent stumbling when cold, it is cut out of the system by the TVSV as soon as it warms up, so capping it off will not affect the emissions. when the diaphragm gets a leak it ends up making the two front cylinders too rich by allow fuel up the vac line and into the intake manifold.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
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Mark
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Re: Fails emissions test - CO too high

Post by Mark »

If you have an oxygen sensor, you have a feedback carb like on my wagon. There is a simple computer that takes the feedback from the O2 sensor and opens a soleniod valve to allow a bit of extra air into the carb if the mix is too rich. In reality, the solenoid valve is constantly opening and closing making the mix swing from too rich to too lean and back again about once a second I think. On average, this makes the mix more or less correct. I think these feedback carbs are tuned to naturally run rich and the mix is leaned out using the air solenoid valve. If this feedback system fails, I assume the mix will revert to the carb's too-rich condition. The factory service manual has the procedure for verifying correct operation using a voltage meter. This lets you see what your mix is at so if it's too rich you can see this for sure instead of just guessing.
O2.jpg
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Rickety Rhino
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Re: Fails emissions test - CO too high

Post by Rickety Rhino »

Petros: the vac line to the AAP does not have fuel in it. It also passes the tests (cold & warmed up) in the Service Manual. And I replaced it 2 years ago, a few months before the last emissions test, which passed.
Mark: test (e) failed, the voltmeter always reads 0. So I did the subsequent checks starting on page EC-32 of the EBCV and Vacuum Switches, which passed until the test of Vacuum Switch B with the engine running, which failed. There was no continuity. So I assume this Vacuum Switch B isn't working. I couldn't find one on-line, and the local Toyota dealer doesn't have it anymore, as expected. Does anyone have one of these, or know where I could get one? Thanks again!
Location: Boulder, Colorado
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Re: Fails emissions test - CO too high

Post by Mark »

My Vacuum switch B failed as well when I tested it (I couldn't find a proper replacement so I replaced it with a furnace vacuum switch), but that shouldn't cause your problem as far as I know. Vacuum switch B only is supposed to have continuity at idle. That tells the computer to shut off the whole feedback system for a more steady idle. At cruising speed, vacuum switch B has no continuity. So your failed switch just makes the computer think you're always at cruising speed and the feedback system should always be working as long as the engine is warm. The fact that you're getting no voltage at all from the test connector makes me think that something might be wrong with the wiring or wiring connections. I'd try to put the voltage meter directly on the oxygen sensor lead when the car is running and see what the voltage is there. It should be between about .1v (very, very lean) and .9v (very rich). Ideally it should be about .5v I think. If you unplug a vacuum line to make a vacuum leak, the mix will be lean and the voltage should drop. If you spray carb cleaner or something like that into the carb when the engine is running, the mix will get rich and the voltage should go up.
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Re: Fails emissions test - CO too high

Post by garyfish »

have you checked the EGR valve?

perhaps it's clogged with carbon and needs to be reamed out so that the diaphragm functions properly

or, if you need to completely replace the EGR valve, Amazon has a couple in stock (Standard Motor Products EGV572), brand new for about $90 + tax and shipping... this price is quite a bit lower than the $130-$150 they usually go for when they can be found
https://www.amazon.com/Standard-Motor-P ... 000C7XX32/

good luck
1985 Tercel SR5 4WD wagon, 300K
1987 Tercel DLX 4WD wagon, 6-speed manual, 260K -- got this one running Jan. 2015 (had been sitting for 2 years); this has been my daily driver since 2016
Rickety Rhino
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Re: Fails emissions test - CO too high

Post by Rickety Rhino »

The EGR valve was indeed very clogged up. I replaced it with the one from Amazon garyfish listed above. This was a PITA because they made the vacuum connection so it was in the way of the big pipe from the manifold. I had to rotate it, then find a way to clamp it down to the body of the EGR, which I did.
But the emissions still failed. CO was somewhat better, went from 42 GPM to 36 GPM, but still above the limit of 30 GPM.
Does anyone have any other ideas? Is the mixture too rich, like the guy at the emissions suggested? What could I do about that?
Location: Boulder, Colorado
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Re: Fails emissions test - CO too high

Post by dlb »

You could try adjusting the fuel mixture screw. It is located at the base of the carb, next to throttle plate. There is a plug over top of it because it was set at the factor and not supposed to be adjusted after that but f* that. I'm no expert but from what I've read in other posts here, this screw only affects the mixture at idle, and just past idle.

The only other way to adjust mixture is to change the jets, I think?

Does higher octane gas burn cleaner, would that help you? I'm sure everyone who has to go through emissions testing already knows about stuff like this but it just occurred to me so I thought I'd mention it.
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Re: Fails emissions test - CO too high

Post by Mark »

Since you have a feedback carb with an oxygen sensor and it doesn't work, your carb has reverted to it's rich condition. If you don't want to get the feedback system working again, maybe try introducing a small vacuum leak in a hose by making a hole in it. Your idle will be a bit rougher, but it might be just enough extra air to lean out the mix enough to pass. I've never tried this or heard of anyone who has tried it, but short of making the feedback system work again or putting in jets with smaller holes in the carb, I don't know what else would work.
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Re: Fails emissions test - CO too high

Post by garyfish »

I don't know if you've tried any "quick-fix" methods to help you pass emissions, but if not, some of them might be worth a try... here's some examples I found through a simple Google search:

https://www.mylucasoil.com/blogs/news/h ... -easy-tips

https://www.amazon.com/CRC-05063-Guaran ... B000CIPUR8

the first 2 minutes of this YouTube video are relevant:
https://www.youtube.com/watch?v=C2ZbrTj ... e=youtu.be

another YouTube video... there are MANY on the topic of passing emissions
https://www.youtube.com/watch?v=5I71er1vxZQ


again, good luck
1985 Tercel SR5 4WD wagon, 300K
1987 Tercel DLX 4WD wagon, 6-speed manual, 260K -- got this one running Jan. 2015 (had been sitting for 2 years); this has been my daily driver since 2016
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garyfish
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Re: Fails emissions test - CO too high

Post by garyfish »

anybody ever try a product like this to help you pass emissions?

https://www.amazon.com/gp/product/B000CIPUR8
1985 Tercel SR5 4WD wagon, 300K
1987 Tercel DLX 4WD wagon, 6-speed manual, 260K -- got this one running Jan. 2015 (had been sitting for 2 years); this has been my daily driver since 2016
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ALiveSR5
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Re: Fails emissions test - CO too high

Post by ALiveSR5 »

Rickety Rhino wrote: Fri Sep 25, 2020 6:22 pm emissions still failed. CO went from 42 GPM to 36 GPM, but still above the limit of 30 GPM.
Does anyone have any other ideas?
My 2 cents. I see that you have tried several things, already, and much more knowledgeable and experienced people on this forum than I have given you their best suggestions.

My Tercel has never failed emissions but I took proactive steps to help ensure that it would pass, such as:
  • Cleaned the cap and rotor contacts or replaced them
    Cleaned and reset or replaced the spark plugs
    Used carburetor cleaner to clean the PCV valve or replaced it
    Replaced the air filter (or blew it out with an air compressor, if it wasn't too dirty)
    Cleaned out the carburetor with lots of carburetor cleaner
    Used Guaranteed To Pass a few weeks before the inspection - Seafoam is also popular
    Gave the car some good hard runs on open highways and high RPMs to blow crap out of the engine
Carburetor cleaner will cause the engine to stall, unless you first hold the throttle open and get the engine revving pretty good.

In PA, after a vehicle becomes of a certain age (25+ years), nobody really cares about emissions results. So, in recent years, I have not known what the emissions values were. Also, in PA, after a few failures, the vehicle can be issued an exemption. Maybe CO has similar rules.

I hope you can find a workable solution.
No other vehicle that I have ever owned had a heart and soul like my 1985 Tercel SR5 4WD Wagon. :D
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