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 » Sat Jul 11, 2020 11:00 am

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 » Mon Jul 13, 2020 10:26 pm

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)
'01 Honda Civic (other daughter's daily driver)

Rickety Rhino
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Re: Fails emissions test - CO too high

Post by Rickety Rhino » Mon Aug 10, 2020 9:41 am

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 » Mon Aug 10, 2020 4:57 pm

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 » Tue Aug 11, 2020 1:39 pm

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 » Tue Aug 11, 2020 4:24 pm

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
Smokey The Brake - 1984 4WD, 230K

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Mark
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Re: Fails emissions test - CO too high

Post by Mark » Tue Aug 11, 2020 9:53 pm

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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garyfish
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Re: Fails emissions test - CO too high

Post by garyfish » Thu Aug 13, 2020 1:22 am

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

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