Fails emissions test - CO too high

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Rickety Rhino
Posts: 27
Joined: Sat Jan 22, 2005 6:03 pm

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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My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

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)

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