My kids'86 244 just failed it's California Smog Test on high NOX. The numbers for various emissions are as follows

15 mph 82 ppm HC (max 133) 0.17% CO2 (max 0.82%) 1765 ppm NOX (max 1146 ppm)
25 mph 69 ppm HC (max 108) 0.14% CO2 (max 0.62%) 1470 ppm NOX (max 1006 ppm)

As you can see, the car passed HC 7 CO2 comfortably, but failed pretty miserably on NOX. I seem to remember that high NOX is usually from a vacuum leak. Is this the case, and would a wholesale vacuum hose replacement be in order? I have until early November to get the car registered.

Thnaks in advance
--
Blane Gardner Couple of Volvos, Couple of Toyota Vans, and an Old Chebby

My '82 runs a WHOLE LOT BETTER after I replaced all the vacuum hoses and engine harness wiring. It was close to failing the emissions tests previously.

As an added bonus, it runs better now than any time in the previous 5 years. At 310k miles, I find this surprising. And a whole lot of fun.
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-- Bruce / '82 244 (298k miles!), '86 745, '87 760Ti, '94 854

nox is caused by high combustion chamber temp and pressure.if you have an egr system make sure it works.if you have access to a gas analyser low co and high
oxygen content would indicate a lean mixture.a vacuum leak generally drives the
hc a lot higher than your numbers.the hot air door is something to check.a combustion chamber cleaning would help.the thermostat may need replacing.deposits coating the cooling system can seriously hinder the ability to transfer heat from the combustion chamber(chemical flush).a failing rad cap may cause hot spots in the cylinder(less pressure lower boiling point).a partly plugged exhaust could cause problems.the timing to 0 might squeak you through.good luck on your airscare.

High NOx is:

1) Vacuum leak (lean mixture)
2) Combustion chamber deposits (must be high volume, bad deposits)
3) bad catalytic converter
4) wrong timing
5) also dirty air flow meter--can reduce NOx by a significant amount as it causes lean fuel trim when dirty.
6) injector seals (again not that likely)

Often CO and NOx readings are inversely related. In other words, CO goes up (rich mixture CO) and NOx can go down because the excess fuel cools the combustion process somewhat.

Just some things to check; vacuum leaks would be a good place to start.
--
1992 940 wagon, very low miles
as well as others.

Chris, a qustion on the timing. The timing marks for the engine do not have markings for degrees. Just a mark for TDC and then some marks to the left and the right of TDC. My Haynes Manual is no help. Do you know what the increments are from TDC?
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Blane Gardner Couple of Volvos, Couple of Toyota Vans, and an Old Chebby

Blane,

Check the airbox thermostat, if it has failed you may be sucking hot air from the preheater hose.
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Bruce S. near D.C.

I would check the basic idle mixture with the diode tool described at the MVP site, and there may be something in the 700/900 FAQ on this. If that doesn't work, take AyeRoll's advice on retarding the timing.

Do you test the oxygen sensor?
Edwin

Set your ignition timing to 0 degrees, and you will pass with FLYING colors. CO and HC will come down a bit too, but NOx will almost be cut in half (well under the amount you're allowed). We've been dealing with emissions tests almost as long as you guys here in CT. The pre-89 cars can benefit from this simple trick.
It's going to run like a dog, so no zipping onto the freeway. Set it back when you're done. Tell them you replaced the plugs or something. DO NOT tell them the timing is off-spec.
Oh, and as an added bonus, your distributor is likely to be frozen. Use lots of PB blaster and be patient.
Good luck!
Rob Bareiss, New London CT

Blane -

When I changed out the air hose (AMM to throttle body) it was a wild guess. The old hose had a small hole, on the underside, that even a mirror couldn't see. The cost was around $20, aftermarket.

How old is the Chebby? I had a '47.

Good Luck,

Bob

:>)

I'll be checking the hoses. The Chebby is a 61 Impala. I put a crate 350 motor in it and a 350 THD tranny in it. I still need to do the rear brakes, floor pans, and get it painted.
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Blane Gardner Couple of Volvos, Couple of Toyota Vans, and an Old Chebby