'79 spider failed SMOG in California - Alfa Romeo Bulletin Board & Forums
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post #1 of 21 (permalink) Old 02-13-2019, 01:38 PM Thread Starter
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'79 spider failed SMOG in California

My spider just failed its smog test. The HC and CO were very low and almost identicle to the 2017 smog test (way down at 13 and 00.00 respectively, MAX is 222 and 1.74). But the NO was higher this time. At the 2017 test the low RPM NO was 800, this time is was 1557 (Max is 1396).
The CAT was replaced in 2015, and has less than 4000mi on it (the spider is a weekend summertime car).
Does anyone have a thought as to what to look for in this situation.
With both the HC and CO so darn low, I have room for adjustment, but what might cause only the NO to jump so much.
I haven't driven the car much in the past few months, but I made sure it was hot when it was tested.
Thank you is advance for any suggestions you might have.
RJG
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post #2 of 21 (permalink) Old 02-13-2019, 01:46 PM
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NO increases with higher combustion temperatures which in turn can be caused by a lean mixture or overly advanced ignition timing. Car manufacturers of that era reduced the combustion temperatures by diluting the combustible mixture with exhaust gas. Some used exhaust gas recirculation but Alfa's of the period rely on the restrictive exhaust manifold. I think that cat converters of that time did not reduce NO.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #3 of 21 (permalink) Old 02-13-2019, 02:48 PM
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there is an aux air pump / circuit that pumps exhaust air into the intake for exactly the reason Ed notes. Your air pump and / or the check valve is likely not working well. My father in law goes thru the exact same thing every two years with his 79 alfetta.

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post #4 of 21 (permalink) Old 02-13-2019, 03:10 PM Thread Starter
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I agree about the CAt. The NOX numbers didn't change much when I replaced the CAt a few years ago.
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post #5 of 21 (permalink) Old 02-13-2019, 03:25 PM Thread Starter
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goats,
I am getting good suction at the pump (increasing with acceleration), so I would think the air would have to be passing through the valve OK. I would have to go through some records, but I think I replaced that valve a few years ago also. It looks newer, and I vaguely remember removing it before.
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post #6 of 21 (permalink) Old 02-13-2019, 03:49 PM Thread Starter
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OK, I found the records. I replaced the CAT in 2014. I replaced the check valve in 2015 when the NOX was almost too high. But the valve was not the problem. I discovered a nut was missing from the exhaust manifold, replacing that greatly lowered the NOX.
rjg
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post #7 of 21 (permalink) Old 02-13-2019, 06:52 PM Thread Starter
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So to clarify. 4 years ago replacing a missing nut on the manifold helped greatly with the NOX.
Today the NOX is very high and I don't find and exhaust leak, pump is functioning.
Wondering what else to look for.
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post #8 of 21 (permalink) Old 02-14-2019, 06:37 AM
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Can you post the report?

I helped a friend get his 76 Alfetta smogged after 10 years off the road. Good engine (75K miles, never apart), good pump. With new cat, HC and CO were zero, NOx was double the limit. Richened it up a hair, that brought the temp down enough to bring the NOx within limits, but with the new cat, CO was still zero. So you have some flexibility on that knife edge.

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post #9 of 21 (permalink) Old 02-14-2019, 09:55 AM Thread Starter
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Here is photo of 2017 and 2019 smog tests.
Unfortunately the print is very light on the 2019 NOx, but the measured low speed is 1557 and the high speed is 991.
As you can see, all numbers between the two tests are very similar, with exception of an increase in %02 and NO.
Only the low speed NOX failed.
So I would expect the problem to be an air leak in the exhaust (which I don't find), or carbon build up and/or dirty injectors.
The car sits most of the time.
I have made no adjustments to the engine since the 2017 inspection.
The valve at the air pump and the CAT both have very low miles on them, and the air pump is sucking as it should.
The car runs and idles beautifully, but is much more finicky to start now.
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post #10 of 21 (permalink) Old 02-14-2019, 10:13 AM
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Exactly, richen up the pump maybe a half turn, I bet the CO stays low and the NOx drops. HC should not change much.
Andrew

Last edited by Andrew; 02-14-2019 at 10:30 AM.
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post #11 of 21 (permalink) Old 02-14-2019, 10:23 AM Thread Starter
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You are referring to the solenoid on top of the SPICA pump, turning that clockwise 1/2 turn?. I thought that was only for idle?
Also, do you think some aggressive seafoam or BG-44 purging would help, since the car sits so much?
I ask this since I have not adjusted the pump in the last 2 years and driven very few miles yet the NOX jumped.
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post #12 of 21 (permalink) Old 02-14-2019, 10:56 AM Thread Starter
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My bad, now I remember, idle is at the air cleaner hose. And counter clockwise for the solenoid to richen.
I really hope I can eventually spend more time with my cars to help keep this stuff straight in my head.
Someone also mentioned backing off the timing a bit to get it passed SMOG. Which is also easy enough, but it would be nice to figure out what caused the change in NOX.
Thank you much for your assistance.
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post #13 of 21 (permalink) Old 02-14-2019, 11:26 AM
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The Fuel Cutoff Solenoid, with the four-tang lockring, is the mixture adjustment. It worked for us on the Alfetta, almost exactly the same readings. We did a half turn richer (CCW), passed with relative ease. No guarantees, but it worked for us. Get it good and warm beforehand, clean plugs, etc. You have decent gas? A smog tech who knows what he/she is doing helps too, but there's only so much you can do.
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post #14 of 21 (permalink) Old 02-14-2019, 11:29 AM
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What thermostat are you running? Car is roughly 175-185* when hot?
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post #15 of 21 (permalink) Old 02-14-2019, 12:46 PM Thread Starter
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I haven't checked it with a scope, but interior gauge has always been consistent at closer to 195.
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