Got the 81 smog tested today, and for the HC test, I hit the max allowed both at idle and at 2500. Yes, I still passed, but want to start thinking about what I can do to prepare for the inevitable next time.

What parts could be changed to improve the HC test results?

 

You've got high unburned fuel. Lots of things....could be O2 sensor, could be catalytic converter not working, carb slobbering,(float level?) engine temp or temp sensor thinking it's cold, low timing...

I'm assuming no codes?

JIM

 

There are no codes right now. I changed the O2 sensor a little over a year ago, along with a full tune up.

I am concerned about the temps. Is that coolant temp that would cause the right burn or oil temp? I notice my coolant temps seem to get up to 180-200, but oil temps rarely get warm unless Im driving on the freeway for a bit.

Im suspect about the cat. Was hoping to avoid that. Seems like a beast of a job.

 

As jim said, it could be a host of things but the fact that your HC (89/71) and CO (.21/.13) are VERY low tells me that your cat is probably not bad...probably....not definitely. If the cat is OEM, I would change it though since a new cat may help resolve the problem. Do you have a readout from the last time before this one showing the readings?

A carb in need of a rebuild will definitely show lots of unburned fuel in the readings...too rich. The correct timing as well as new plugs if yours are fouled would help (new coil, performance control module in the HEI, high voltage HEI coil, ignition wires....possible engine miss?).

AIR pump working correctly injecting air into the exhaust ports for more complete combustion?

High NO usually indicates a malfunction EGR valve which takes unburned fuel and reintroduces those gases into the intake for reburning. On my 94 Mustang GT when I recently blocked the EGR valve gases from entering the intake (fooled the computer so no check engine light), 2 things occurred with the removal of the EGR:

1. The engine temp runs noticeably cooler now...eliminated pinging under load
2. The NO jumped noticeably on my last emissions test, although I passed as well. On my mustang the EGR valve operatings under ALL rpm conditions, unlike the 81 C3 I believe, but it tells you how the EGR effects the NO reading...

On my 94 mustang GT, I can tell you that no EGR, BBK shorty headers, magnaflow X pipe with 4 high flow cats, Magnaflow mufflers, eliminating the EXTREMELY HOT transmission lines from the radiator cooling (2 external double stack coolers now) resulted in a noticeable drop in the engine coolant temperature which definitely effects your ability to pass emissions. Last year, the mustang initially failed the emissions until I told the operator to let it idle for 5 minutes (it had been sitting engine off for a while) and retest. It passed once the engine was hotter than the first test. Your L-81 running 180-200 is marginal...I would say 200 should be the minimum coolant temp..somewhere between 200-220 is ideal for emissions.

Lastly, I don't know if this stuff works BUT in other states (probably not CA since everything seems banned there) you can buy "emissions pass" that you put in the tank with like 3 gallons of fuel in the tank...You can probably buy it on line if not available...MAYBE but not sure it works....

There are many ways to skin the cat and with pretty decent numbers to start, the above should give you some guidance on how to pass the next time. If you can find someone with sniffer equipment to monitor the engine with some of the suggestions above BEFORE you get tested next year, you will know exactly where the motor lies in terms of emissions before the pollution ****'s (ridiculous on a 81 C3 that is 35 years old!) have their test.

Hope that helps!

 

To get good (low readings) you need to get the car fully warmed up. 20 minutes of highway driving. It takes longer for the oil to reach operating temp than the coolant.

Once you get to the testing facility, avoid waiting with the engine off. Lowest readings will be if you can test right after arriving when everything is still hot.

Your HC at max tells me (lack of) heat is the problem. The test will have a grace period where they keep measuring to see if the values drop to a pass. As soon as they do the test stops. Your car was warming up during the test and the readings were decreasing. When the readings got low enough to pass the test stopped. That's why your HC reading is so perfectly at "max".

 

High HC is very often caused by too much timing advance. Advancing the timing makes the combustion cooler, and you run much higher HC. It's a common, and effective, tuning trick to advance the timing, and to run the vacuum advance off manifold vacuum, to get better power and throttle response. But this will run the emissions way up. To pass emissions, make sure you're running your initial timing at or below the ridiculously retarded factory timing specs, and make sure you're not running manifold vacuum to your distributor (should be ported or routed through functional vacuum/temperature switches).

To give you an idea how effective retarded timing can be in passing emissions, we ran our 10-second roller-cammed 1050 Dominator-equipped '69 Camaro drag car through the Colorado emissions testing program a few years ago in order to get plates on it (so we can run it in the "street" classes. Colorado has since deleted the requirement for any testing of pre-75 cars, but a few years ago, you had to pass an initial test to get plates on any car). This car normally idles at 1800 rpm, and max for the test was 1200. We retarded the timing from 36 degrees locked out to "zero." This required forcing the idle speed screws WAY in just to keep the thing idling at 1100. The headers were glowing red in daylight. And the car passed emissions.

Lars

 

Original specs for your vette were
co 1.2
hc 220
nox gases weren't even checked back then.
To drop your hc retard you base timing 2 degrees for inspection. That will help. Your cat is getting weak because of your NO numbers. They will only get worse. The worst thing you can do is let the engine and exhaust cool off while for them to get to your car. The single wire O2 sensor has to be at least 600 degrees before it will function properly. Same with the cat. It has to be hot before it will "light off" inside.

 

Another option...

Find a DMV exempt zip code close to where you live, for me it is Julian zip code 92036, go to the post office about 6 months before registration is due and get a PO Box.

File a change of address with the DMV to that PO Box

No more biannual smog check for you and you have done nothing illegal

 

For the test you are allowed 2 degrees from factory on the sticker.

So make sure you check were its at. If you retard it 3 degrees they will fail you.

Also they have been slowing lowering the passing numbers. I had a 84 Mustang 5.0 factory Holley. I was keeping the results paperwork when I noticed they reduced the MAX which placed me right on the edge.

http://www.bar.ca.gov/pubwebquery/cu...VLTROWID=14103

 

Yep, That is how they are weeding out the older cars.
Original specs for 1976 were 7.5 Co and 750 HC. That's almost raw gas dripping the tailpipes.

 

OP: How many miles on your oil? Just curious if the PCV system is inhaling raw gas fumes from the hot oil, bumping up the HC levels.

Also, I'm curious if putting in a couple gallons of E85 into the tank would add enough extra oxygen into the combustion process to reduce the HC level.

 

Looks like the fuel control is pretty decent so assuming the engine itself is in good shape, other than a tune up there's really not much you can do to get the numbers down except replace the aging cat.
I'd suspect that if you replace the cat before the next smog the numbers will look good.

 

I realize now I had it all wrong. I went first thing in the morning. Smog shop was only a few miles from my place, so the coolant temp warmed up, but the oil was not fully warmed up at all. When I called the smog shop the day before, he said that the excessive heat for these cars causes them to fail, which is why I went early in the AM.

I could have driven for 10 miles or so on the freeway, and the oil temps certainly would have come up. About a 2 years ago, I did a full tune up on the car (plugs, wires, cap, rotor, o2 sensor), and I have probably only driven the car around 2000 miles or so since.

I have not replaced the PCV valves since I have owned it. Ill do that for sure.

I didnt mess with the timing. I need to check that as well next time.

Im guessing the cat is original. Certainly hasnt changed since Ive had it, and it looks pretty old.

Im really hoping I can find the time and money to get the LS1 installed before the next smog, but thats a long shot.

 

My 74 BB barely runs 180-195 in 90 F weather . The Carb is as loose as a 100 year Winchester 30-30 rifle and engine never overhauled. She loves to sip gas.

I bet my car makes more pollution than any 10 new cars combined, maybe more . I'm sure it is a pollution monster of the first order.p

I can't move to CA ....LOL

 

 

What the EGR actually does is introduce un burnable or already burned exhaust gases back into the intake tract to cool combustion temps because they can't burn a second time to reduce NOX emissions, cars usually ping worse with the EGR removed unless other mods are done at the same time. HC and CO will go down dramatically by retarding the timing.
I did Ca. smog for 27 years.

 

You would be exempt like me

 

Another thing to consider is that the cats back then were VERY restrictive. Just replacing it with a modern cat will get you an easy 20-30 horsepower.

 

Retarding the timing 1 or 2 degrees would drop you well within the limit unless it is already at zero.

 

Another trick I have used in the past is find a gas station with E85 and put a couple gallons in with only a couple gallons of regular gas. The extra alcohol with lean out the mixture and reduce the HC count. Then immediately after the test fill it up with regular gas. I used to have to do this each year for my Camaro.