Emissions, Emissions, HELP??!!

[wicky88s1975]

Hey All, After four months of reading, working on, and learning the hell out of my 75 coupe I've just about got her Smog legal for California. I started her up last week for the first time since bringing her home from arizonia. What a feeling of accomplishment!!!! Then the Smog Test FAILED. Running too rich is the diagnosis. Its a 350, with a Quadrajet. all emission gear on and working. The Rodchester book is a bit confusing with me only having basic knowledge. Where do I start?

Thanks to all in advance, Jim

 

[Stingray72]

Well, I have no experience whatsoever at passing emissions tests, but I do own a Quadrajet. I would try leaning the idle mixture. If the "Rochester" book you're talking about has a black cover with a top view of a Quadrajet with electronic controls, I have the same one. Good book. Anyway, it explains the process in there somewhere. It's not difficult. You'll need a special screwdriver that you can get at NAPA for about $6 because the screw heads are sort of shaped like a "D", and a vacuum guage could come in handy. If the mixture is already adjusted for best vacuum, it shouldn't hurt to adjust it to the lean side a little bit to see if you pass.

Good luck.

 

[rpounds]

Wicky,

Aren't California emissions tests wonderful?

I have a 75 also. Trying to diagnose exactly what is wrong by long distance can be a bit difficult. However, you should have been given a read out of the various emissions. If you can post what your readings were along with the high/low limits, I may be able to help.

Beyond that, I would look for a good repair shop that can give you some advice. The most obvious to me would be the cat-converter. After that many years, they have a tendency to not be very efficient, not to mention restrictive.

Let me know if I can help.

Ron

 

[WhalePirot]

It's a tightrope, that leaning. Too lean drives up the NoX, which will fail the test, too.

The Carb Shop, in Huntington Beach has a good reputation.

 

[wicky88s1975]

Thanks guys, this is a pain and a shop maybe the wat to go, but I'm determined to learn about this thing.

 

[wicky88s1975]

The readouts from the last test are as follows: 15mph test, 1346 rpm, CO2%- 11.0, O2%- 3.7, HC(ppm) MAX- 194, AVE- 57, MEASured- 193, CO(%) MAX- 1.26, AVE- 0.25, MEAS- 1.88, NO(ppm) MAX- 1286, AVE- 570, MEAS- 64 (FailedCO%) 25mph test, 1365 rpm, CO2%- 10.6, O2%- 4.0, HC(ppm) MAX- 161, AVE- 45, MEASured- 176, CO(%) MAX- 1.06, AVE- 0.19, MEAS- 2.21, NO(ppm) MAX- 1146, AVE- 648, MEAS- 36 (Failed HC and CO%) Ron, I hope you can help with this. Stingray, I do have that book, and the tools, I just don't have the experience yet to decypher all the lingo and part functions. Thanks

 

[rpounds]

Jim,

I'm certainly no expert but after looking at your numbers, I would still be suspicious of the catalytic converter. I am assuming that your engine is basically stock and in good running condition (rings, valves, good compression).

Question - are you running the original exhaust system? Back when these things were new, leaded gas was still available and, even though the fuel filler necks were sized so as not to accept the nozzle of a leaded fuel pump, many people modified their filler necks so as to take advantage of the lower price of leaded fuel. Unfortunately, this destroyed the affectiveness of the catalyst. The newer design of converters is much better than the old "platinum ball and bead" system originally used on 70's vehicles and can be purchased for a very reasonable price.

Also, your car should be equipped with an AIR pump. As crazy as this may sound, the main purpose of the pump is to dilute the exhaust gases as they travel to the catalytic converter, by forcing clean air into the exhaust stream. This extra air (actually the resultant oxygen), enhances the burning of exhaust contaminants in the cat converter. If the pump is not working correctly, it can cause the converter to be less affective.

There are a number of other things that affect emissions including timing. Initial timing as well as the advance curve can have a dramatic affect on the smog test. That's the reason why advance curve kits are illegal in California for emissions controlled vehicles. A worn out distributor, especially if the advance curve has been modified, can contribute to high emissions.

A vacuum leak can cause problems with the test. Corvettes this old are notorious for having vacuum leaks. A vacuum leak will drive up your NOX.

The original jetting of the carburetor may have been tinkered with over the last 27 years. I'm not sure what the original jets and metering rods should be with your car. I'll try to find that information (without tearing mine apart)

Another thing I should mention is running temp. If your car cools well and you are running a lower than stock temp thermostat, your emissions controls will not be as affective. Stock 75 Corvettes in California ran a 195 degree thermostat. Most of us run a 180, just for the mental comfort that the lower temperature brings. However, I have to change mine out before smog tests. Otherwise, I'll go down in flames. Also, always make sure that the engine is completely warm before going in for the test. Take a 5 or 10 mile drive before running it in for the smog test.

I hope some of this helps.

Ron

 

[wicky88s1975]

Sorry, I forgot to mention that a new high flow Cat was installed last week. The timing is set at 9 btdc at curb idle and the distributor is newer HEI, installed in December last year. The carb is a rebuild from a good carb shop locally (#7045224). Which makes it the correct carb for this year car and type It is a 49 state carb, but the car is from outside CA. As for the metering rods and jets, I'd have to check with the shop on Monday for any additional specs. The themostate I'm running is a 180.
This weekend I am installing a new set of Boush Plat Spark plugs. Should I replace the thermostate?
All other suggestions at the end of your post were done before the test. Thanks again
Jim

 

[wicky88s1975]

Question: NOX? is this the NO reading on the test?

 

[rpounds]

From the California Air Resources Board Website:

Nitric Oxide (NO): Precursor of ozone, NO2, and nitrate; nitric oxide is usually emitted from combustion processes. Nitric oxide is converted to nitrogen dioxide (NO2) in the atmosphere, and then becomes involved in the photochemical processes and/or particulate formation.

This is the NO on your read out, sometimes referred to as NOx.

You may want to check out their web site. It is has some good info, although getting really good information out of any government agency is like pulling hen's teeth . . .

The web site is:

http://www.arb.ca.gov/homepage.htm

 

[rpounds]

PS . . . yes, put in the 195 thermostat. There should be two thermostatically controlled vacuum switches on your engine. One is normally open and the other normally closed. The normally open one controls the vacuum to your heat riser (yes it's thermostatically controlled on a 75). The other one controls your vacuum advance. They do not switch states until they reach very close to the 195 degree mark.

One of the reasons for the higher OEM thermostat was to reduce emissions.

 

[WhalePirot]

Good luck with the Bosch plugs. I opted for the +4s, and every performance engine guy I talked with said to use other, like Accel or Champion. The electrode size in the Bosch is very small, which apparantly affects the initial flame size and totality of the burn.

Heck, even the BMW guys don't use them!

 

[Buckskin7T7V]

Years ago, I put in a Jacob’s Electronic Ignition Computer.
My 77 ran so clean, the smog machine would not kick in to do the reading. We spent 45 mins making it run richer, to get the smog reading. I passed only after I made the car more of a polluter. The CA test makes no logical sense. It is a money maker for the state. If they really cared about car pollution, we would have a better mass transit system.

 

[wicky88s1975]

Ok, guys......leaned the mix(curb idle), new plugs, checked everything.... The numbers at cruise sky rocketed GROSS POLLUTER..
I went to my Carburator shop and the broke down the problem for me. finally came up with smaller jets, and a lean mix (set on the dyno this time),check the fuel pressure again. I went through evey system an found only that the charocoal canister was not getting a vacume. would this do anything to cause a rich mix? .....Wish me luck I Go back tomorrow

Thanks for all the help....(I'm really interested in the igition computer) tell me more please

 

[rpounds]

I'm not sure about the charcoal cannister . . . I wouldn't think that would affect the tail pipe emissions, but I could be wrong.

Out of curiosity, what jet and needle numbers did you end up with? I believe that stock was somewhere around .073 jets and .050 needle.

I'm anxious to hear your test results!!

Good luck,

Ron

 

[wicky88s1975]

Going with .071 jet and .046 needle. Carlos at Burbank Carburator thinks it will solve the problem but it will run like crap. I test drove it today and found evetything good a high speed and chuggy at idle. Just like a Vette doesn't want to go slow!!! I'll post the results tomorrow if I don't kill myself first. HA HA

 

[wicky88s1975]

Ok, Guys I got back from the test and I passed with flying colors. The new additions were
.073 jets replaced by .071
Rods stayed the same at .046
Leaned the mix to bearly running at idle , fine when warm
same 180 temp thermostate ( the TVS's work @ 165)
Linked the canister vacumn into the PCV (vacumn for sure)

Here are the first results

The readouts from the last test are as follows: 15mph test, 1346 rpm, CO2%- 11.0, O2%- 3.7, HC(ppm) MAX- 194, AVE- 57, MEASured- 193, CO(%) MAX- 1.26, AVE- 0.25, MEAS- 1.88, NO(ppm) MAX- 1286, AVE- 570, MEAS- 64 (FailedCO%) 25mph test, 1365 rpm, CO2%- 10.6, O2%- 4.0, HC(ppm) MAX- 161, AVE- 45, MEASured- 176, CO(%) MAX- 1.06, AVE- 0.19, MEAS- 2.21, NO(ppm) MAX- 1146, AVE- 648, MEAS- 36 (Failed HC and CO%)

Here are the final results:

15mph test, 1694 rpm, CO2%- 10.2, O2%- 6.5, HC(ppm) MAX- 194, AVE- 57, MEASured- 49, CO(%) MAX- 1.26, AVE- 0.25, MEAS- 0.00, NO(ppm) MAX- 1286, AVE- 570, MEAS- 570
25mph test, 1672 rpm, CO2%- 10.0, O2%- 6.8, HC(ppm) MAX- 161, AVE- 45, MEASured- 29, CO(%) MAX- 1.06, AVE- 0.19, MEAS- 0.00, NO(ppm) MAX- 1146, AVE- 648, MEAS- 648

As you can see CO@ at 0.00 HC, down considerably, and NO wet up to just below the average.....I learned way more than I wanted to about Emissions than I wanted but it's done and I can move on to the Fun Stuff.....Front End rebuild next Thanlks again for all the help hopefully this thread will help others get through the dreaded CA emissions

 

[rpounds]

Congrats Bro!! It can be a pain. Another few years and we can kiss the testing goodbye for our '75s!!

Ron

 

[wicky88s1975]

You got that right I'm already starting to write down the Mods

 

[rpounds]

It's actually pretty amazing what you can do and still be legal. Comp Cams has a line of CARB legal bump sticks, anything from low end torque to high RPM power. There is a good selection of heads from AFR, Dart, etc.

As you found out, tuning the carb on a dyno after any kind of modification is mandatory - definately not a luxury. Not only for your emissions status, but for max power. An overly rich carb is just as deadly to a power setup as is an undersized or under jetted carb.

Anyhow, good luck on the mods and congrats on the pass!!