Failed CA smog test; high HC at idle

M

mike76c3

Well-known member
Joined
Sep 5, 2008
Messages
101
Location
So. Cal.
1976 L48 odometer reads 70K+ (not sure if it rolled over)
- Edlebrock Performer intake
- new distributor/cap, plugs, EGR, carb rebuild by SMI, all in 2016, 3K mi. since
- not sure most recent oil change, think it was 3/2018
- mostly highway miles, 3K MSL give or take (high desert), usually 16mpg
- needs about 1/2 qt oil approx. 1.5K mi.

First test 7/2018, ambient temps low 90's, humidity pretty low
thum_5725ca68b5bed885.jpg

Found #1 plug wire arcing to exhaust manifold, #6 boot crumbled,
so replaced all plug wires. Checked new wires' resistance, was
within specs (but didn't record values).


Second test 12/2018, ambient temps low 60's, humidity pretty low
thum_5725ca68b5c1ed86.jpg

Not sure what to make of the low HC at 25MPH, especially the second test. Tried to understand what all the gas values mean, but didn't have much luck (all the sites that came up seemed to be quoting from the same source). All the lambda calculators I could find seemed to require an entry for NOx, which apparently CA doesn't test for anymore.

Thinking the high HC value meant some kind of ignition failure, I pulled the distributor cap. Looked good (minimal pitting). I pulled the plugs; didn't find any that were wet (car's in garage, haven't been able to get doors open, so couldn't do procedure to properly read the plugs). #8 had some whiteish/light tan deposits. Pulled the EGR; both it and the intake manifold looked O.K. (failed a previous test because original manifold was plugged and EGR was bad).

Once I can get the garage open I will try to check the EGR, read the plugs, and do a compression test.

In the meantime, based upon the smog test results, any advice on what to target?

Thanks,
Mike
 
License the car as an antique. Most states don’t do safety or emissions on cars registered as antiques.

There are lots of things you can do otherwise, but are they legal? Some guys claim changing the tune up (extra lean) helps pass emissions, then change it back.


“Classic cars do qualify for a smog exemption in California. By definition, a classic or antique car is any vehicle that is 25 years or more old. Since cars built before 1975 are exempt from the California smog certification program, owners are not required to have their vehicles checked for smog-producing emissions”
 
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I sympathise with your plight. I wish I understood the relationships and tradeoffs better. I think HC is too much fuel but have no idea about reducing CO's. I know I always had to lean out my old Jag to just barely running if any hope to pass. Anybody know of a paper or treatise to clarify the issues?
 
Thanks for the replies.

RE: antique/collector status in CA

1. What is a collector car?

A collector car is used primarily in shows, parades, charitable functions, and historical exhibitions for display, maintenance, and preservation. It cannot be a vehicle used primarily for transportation. [Vehicle Code §259]

There is proposed legislation to change the current exemption from '75 and earlier to something like '87. However, I think this gets proposed just about every year, and hasn't happened yet. I'll keep my fingers crossed, but won't hold my breath. When I bought the car, the rolling exemption that was about to cover '76 instead was capped at '75. I didn't realize that until after I bought the car. Should have picked up on the fact when suddenly '76 prices went soft . . .

In the meantime, usually the car passes, including 2 years ago. The two times it's failed in the past have been due to mechanical failures (blocked/failed EGR, and failed air/smog pump). So, something mechanical is likely the issue now. I don't know how many if any of the tips on various sites can compensate in my case. I think it would end up being easier to just find the problem and fix that.

High HC is unburnt fuel. Most of the info I found says you can narrow down the cause based on the CO2, O2, HC, and CO values. However, the values are described in relative terms ("high" or "low"), but I couldn't find what specific values equated to those terms. The test results list values for HC and CO (mine are High and Low), so I just need to figure out CO2 and O2. If I can find a lambda calculator online that doesn't require a value for NOx, that will also help narrow down the problem. I may have to resort to finding the equations used by the calculators and just figure it out myself. The calculators also derive a relatively accurate AFR from the gas values, and I'm kind of curious to see what mine is.

Thanks,
Mike
 
You are running too rich, high HC is unburnt fuel. Go through the carb, or just lean it out. Make sure the air pump is working.
 
Just putting this out there, there are states that don't test cars at all.... like Washington.... just think, you can make your Corvette fast and not have to worry about 'the Man' holding you down

it does rain a bit here, though. :mullet:
 
The last time I went to WA they kicked me out -- I don't drink coffee :amused:

Once I found better wording to use when searching ("exhaust gas analysis", "Exhaust gas percentage", etc.), my results returned useful info. At the ideal AFR (14.7:1):

- CO2 should be around 12%. The more efficient the engine is running, the higher CO2 will be.
- O2 should be around 1% to 2%. The higher the O2, the leaner the mixture. However, too high O2 (> 3%) can impact accuracy of CO measurement.
- HC should be around 100 PPM. High HC can happen when mixture is rich or lean; most very high HC readings happen when mixture is lean (not enough O2 available to burn the fuel)
- CO should be around 1% to 3% depending on RPM. Lower is better, higher indicates unburned fuel.

From my last results, looks like the O2 is high. Usually high O2 and low CO means the AFR is lean. However, too high O2 can impact accuracy of CO measurement. Most likely cause is a lean misfire. So, troubleshooting that is the path I'll start with.

One thing I'll check is fuel pressure. When I put the gauge in the line from the pump to the carb, I'll check the filter. Is there an easy way to check the sock in the gas tank?

Tentative plans are:
- Some type of de-carbonizing
- While motor is warm, change oil and filter
- While car is up to change oil, replace plugs
- While plugs are out, check compression
- Put pressure gauge in fuel line to carb
- Also hook up vacuum gauge somewhere on carb or intake manifold
- Put everything back together
- Run motor to check pressure and vacuum
- Hopefully fix whatever issue is discovered by diagnosis.

Thanks,
Mike
 
Did it pass smog in 2016,17,18?
When did you change the intake
Only 3,000 miles in almost 3 years, sits a lot
Carb could be lacquered up
 
mike76c3 said:
The last time I went to WA they kicked me out -- I don't drink coffee :amused:
Click to expand...

no tar and feathers? You got off lucky, the last guy who admitted that here, they tarred, feathered and painted him green and blue.

Proper Court attire here is flannel shirt, long hair and ratty jeans.

my vote is on varnished carb.
 
I know a varnished carb really should be taken apart to clean it . . . but . . . not really wanting to bite that bullet right now. Can I get away with something like B-12 Chemtool or SeaFoam? Had to devote some time to my primary vehicle, but hope to get in some quality time with this car over the weekend.

Can't find the test results from '12, '14, or '16 to compare the numbers, but it did pass each time. Did the intake in '12. My mom's been needing some assistance due to a bad back (can't drive right now), and I became a first-time homeowner three years ago, so a lot of my time is spoken for. Takes me awhile to get basic maintenance done on either vehicle. Plus, there's a couple months in the summer when it's just too damn hot, and a couple months in the winter when it's too damn cold. So, lots of things that make it easy to say "I'll get to it tomorrow".

Thanks,
Mike
 
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