ksems

Hi all,

Went and got the car tested this afternoon.
Failed the NOX level. Nitrogen Oxygen.
From what I understand this is usually an EGR valve problem.
Anyhow, the EGR was replaced 2 years ago when I failed the NOX then :(
Is it time for a new Catalytic converter?....mine is original.
The car got a 2903 .......1047 is the highest number that one can have to pass.. So you see, I failed miserably.

Thanks for any help.
Kevin


[Modified by ksems, 2:16 PM 3/14/2002]

BadjerJim

YES.. you need a new Cat Convertor. I put a high-flow cat in my 1981, and the difference was amazing. Lower, deeper tone, better acceleration, better everything.

GM's cat designs from the earlly years (like yours) are simply crud. They plug up fast.

Don't begrudge the money. Should be less than $200 (installed). You gotta have it to pass emissions anyway.

Good Luck!

-BadjerJim

gerry72

NOX is generally caused by high combustion temperature. Most of the time it is due to a lean mixture or timing too far advanced. Check your timing and fatten up the idle.

ksems

Hey Badger....
thanks for the quick reply.
Where did you get your converter/What kind?

Im going to order it today....quick.
I only have a week before I am overdue with my test .....I know...I should have not waited till the last minute!!:mad:

I think I can put it on myself...its just bolt on and I actually had it off last year so the bolts shouldnt be too tough to loosen

recommendations anyone ?
Thanks
kevin

ksems

gerry ,

I had the plugs out last week and they all looked perfect...no carbon...
nice brownish /white....
would it not show a lean mixture on the plugs?.........?

if temps were too hot wouldnt they be really white and glazed?...maybe even blistered?

Kevin

gerry72

Not talking about too hot, too lean, or too far advanced, Kev. I'm talking about the difference in having an engine perform at peak efficiency and what's required for emissions. They are two, often opposed, issues. We know that adding timing really improves the way a car accelerates, but that also increases NOX due to the higher combustion pressure. Same thing with running a little lean. The best HP occurs just to the lean side of stoich, best torque on the rich side, but richer mixtures reduce combustion temperature which reduces NOX. I'm not saying richen it up to the point of carbon-fouling the plugs, but to richen it up to the point where it cools the combustion temperature. You're not likely to see this dramatically in the plug. Juggling the emissions equation is a little difficult. You want the mixture rich enough for you to get past the NOX, but not so rich that it fails CO.

81VETTOM

put on a Random Technology converter, difference was amazing. Also, change oil before you go, older oil will effect tests. I agree with other suggestions to. good luck

73Ken73

Like the other poster is saying, retard your timing. Retard the timing until the engine has no power and it should pass emissions.

ksems

gerry - I see , thanks for the explanation :)

I did get a tune up last year and I know he said that he advanced the timing a bit.....It is really running pretty good right now...especially once I get past
45MPH....whoo hoooo..
Ive never set the timing myself before...I theoretically know how its done, but have never done it...I may be a busy man this weekend if someone can walk me through the process...- yes?...no?

Random Technology - Ive heard of them...pricey, pricey...Ill have to look into that..those need an adapter kit if I remember correctly ..whats the adapter all about?

Thanks
Kevin

Kingt

Does the car have an air pump? High NOX can be caused by incomplete combustion due to lack of oxygen. The air pump supplies air to complete the combustion process. If there is a problem in the air pump system it can cause high NOX readings. I don't know if your model used one or not?

:flag

Gator81

Hi, Kevin!
I agree with the others about replacing that old cat - you will not believe the kick in the pants your '81 will get from that! The first time I ever heard my '81 bark rubber in second gear was on the way home from the shop after getting a new, modern, brick-type cat.

However! The fact is that a standard type cat (including the original) was never intended to reduce NOx emissions. That requires a different catalytic material than what is in your original cat or in any stock replacement cat for your car. If I remember right, the platinum catalyst splits HCs apart so they can combine with the oxygen that is getting pumped into the cat via the air pump on the '81, to make H2O and CO2; in later cars there is a second catalyst, paladium, that actually splits the NOx apart. That's why newer cars don't have an air line to the cat - the paladium produces oxygen from the NOx, and the platinum uses that oxygen to oxidize the HCs, so no other air is required.

That brings me to a bigger question: Why in the hell are they failing your car for NOx? Are you SURE it's NOx that's failing? I mean, I didn't think it was possible to fail NOx with an '81, because I didn't think there were NOx standards for an '81. That's why the '81 doesn't have a catalyst for NOx! Is it possible the tech monkey plugged in your car as a '91 by mistake???

Good luck! :seeya

ksems

yep - I have an air pump....original......dangit....I hate emissions.....
I dont know where to start.....

I just called Random Tech...they have the converter but the adapter will take at least a week to get in...I dont have the time.:mad:

I dont mind throwing a little money at it..I just need to make sure its the right money for the right part....

Kevin


[Modified by ksems, 3:00 PM 3/14/2002]

ksems

please tell me that swapping out the 195 thermostat with a 180 wouldnt have any affect on my NOX :confused:

Kevin

zwede

A 180 would improve the NOx. Lower temperatures = Less NOx, but more HC.

Check the rest of your EGR system. Maybe the Valve itself is good, but the hoses cracked? There's also a temp switch that prevents EGR at low engine temps. Maybe it has failed.

You shouldn't have 2000 ppm NOx even without a cat at all.

Also set the timing back to stock or slightly retarded. Makes a big diff in NOx.

Gator81

I'm no expert, (standard disclaimer), but...

I would expect the cooler temps to actually reduce NOx. As I understand it, NOx is a product of very high combustion temps and pressures. That's why the EGR brings spent gases into combustion at idle, to dilute the mix and reduce temps and pressures.

If I had a NOx problem, I'd be looking at the EGR.

I still have a hard time believing you have to make an '81 pass a NOx test.
:confused:

ksems

Gator - I know, this year 76 and newer cars have to pass...the only times that my car has failed, it has always been NOX.....Im a little peeved about it.


zwede.......I need to learn how to set the timing...........never done it...
understand the theory though :)

Kevin

ksems

I know the thermostat thing sounds wierd, but its actually listed on the

"possibilities chart" on failing NOX...

oh well

ksems

Napa has the converter in stock for 166.00
I may have to go that route in the interest of time.
I hate that I have no way of knowing until I get tested whether I fixed the problem or not...:(.......did I say I hate emission?......well, if I didnt...
I hate emissions......

Garys '68

2 questions, is the car tested at idle or on a dyno? Do you have a Q jet or Carter carb?
If it's an idle test, I would turn the air control screws out 1 turn and back the timing off a few degrees. That's a lot cheaper than replacing a cat that may not affect NOX levels.
My $0.02
Gary

Gator81

To get the base timing correct, you have to unplug the computer advance. There's a connector in the harness for that. Your manual will tell you how to find it.

However, in your case, that's not really necessary. You just need to set your timing back a bit to pass the test, then reset it to where it is now.

Here's all you need to do:

Use a solvent rag to clean off the timing marks on the damper. Use a black marker, like a sharpie, to highlight the marks in the 0 to 10 BTDC range.

Hook up an inductive strobe timing light. Black clip on the alternator mounting bracket, red clip on the alternator output stud (it's under a rubber boot), and clip the pickup over the wire to plug #1.

Shoot the light at the damper, and note which line the pointer points to.

Slightly loosen the bolt that holds the hold-down clamp on the base of the distributor. It should be 9/16", I believe. An "offset" distributor wrench, $5 at any autoparts store, makes that much easier.

Turn the distributor just a little bit until you hear the engine rpm fall off. Recheck your timing with the light. Note where it is.

I'd drop it by 4 or maybe 6 degrees, and don't forget to tighten the distributor clamp. Try the test again and see what you get.

That's it. If you pass, then just un-do what you did, and you're good until next year!

==========

I don't mean to keep running over a cat that's already flat, but I believe you're barking up the wrong tree about the converter. (Is that the max legal limit of mixed metaphors? :D ) I'm certain your car needs a new catalytic converter, for more power and fuel economy, plus lower HC and CO emissions. But if your car never had a NOx catalyst in the first place, and it is still failing the '81 standard for NOx (whatever that might be!), then it is illogical to believe that the converter is at fault. But, since it DOES have an EGR, intended to reduce NOx (among other things), then it IS logical to suspect that the EGR is at fault. OK, OK, I'll shut up now. :rolleyes: