Emissions / Tuning Advice

shrouded · 07-06-2004, 09:49 AM

My 82 SC failed its emissions test yesterday. I plan on taking it in to the shop for a tune-up, and to see what they can do with it in a few days. Between now and then, I am interested in hearing options for things I could do to help the situation myself... or just to learn about what my local shop may end up needing to do so I understand what is going on.

Does anyone have suggestions for me? I have a good set of hand tools and timing light. I don't have a surplus of knowledge or experience (I changed the oil myself for the first time over the weekend), but follow instructions carefully and competently (used the 101 Projects book to upgrade to the oil-fed chain tensioners last year without incident).

The car failed the test due to low speed RPM (1309, needed to be under 1200), but probably would have failed anyway, as CO at 2388rpm read 3.18.

SC-targa · 07-06-2004, 01:51 PM

What were all of the readings? Do they have a NOx test as well as CO and HC? How old are your plugs? Is your ignition timing set to factory spec?

It may just need to be slightly leaned out.

Regards,

Jerry Kroeger

shrouded · 07-06-2004, 03:15 PM

Quote:

Originally posted by SC-targa
What were all of the readings? Do they have a NOx test as well as CO and HC? How old are your plugs? Is your ignition timing set to factory spec?

It may just need to be slightly leaned out.

Regards,

Jerry Kroeger

Thanks for the reply. The plugs are ~9 months old. I'm not sure where my timing is set (I haven't touched it). I didn't adjust the timing after updating the chain tensioners, so it likely needs it.

These are the full numbers:

High:
RPM - 2388
HC - 187 (limit 220)
CO - 3.18 (limit 1.20)
CO2 - 11.5
O2 - 2.78

Low:
RPM - 1309
HC - no reading (skipped because RPM was too high)
CO - no reading (skipped because RPM was too high)
CO2 - no reading (skipped because RPM was too high)
O2 - no reading (skipped because RPM was too high)

Paulporsche · 07-06-2004, 06:50 PM

See what happens when they set the CO to 1.2%.

You may want to reset it to 3 or so after the test.

Paul

stlrj · 07-07-2004, 04:45 PM

I thought everbody knew you had to lean them to pass smog and then set them rich to make them run the way you want later.

Joe

shrouded · 07-07-2004, 08:48 PM

Quote:

Originally posted by stlrj
I thought everbody knew you had to lean them to pass smog and then set them rich to make them run the way you want later.

Joe

Hehe. I think I have picked up the concept from reading old posts. The issue is that I'm shy on the details of how to do those things. With something like Wayne's book spelling it out I do pretty well... but with as little knowledge as I have I'm hesitant to go start fishing around without a little guidance.

Can you fill me in, or point me in the direction of a good thread I might have missed?

Paulporsche · 07-08-2004, 03:28 AM

You adjust the mixture with a 3mm Allen wrench fitted into the hole on the top of the mixture control unit. If you have a gas analyzer, such as a Gunson, you can tell what your setting is. Without one, there is no way to know the actual %. There are lots of threads on this.

Perhaps a fellow lister in your area who has a tester can help you or you can go to a mechanic who has an analyzer and he can set it to 1.2.

The general finding seems to be that 1 full turn on the mixture is approx equal to 8%. Clockwise, when seen from above, richens the mixture.

Paul

shrouded · 07-08-2004, 02:32 PM

Well, I already have an appointment scheduled to have a pro look at the car next Tuesday. Until then, I am going to try to play with this as I can, if for no other reason than to learn a bit more.

As I understand it, (digging through old threads) adjusting the A/F only changes things at idle. If I lean it out, I should expect my idle to drop.

Will that help in any way with the high CO numbers I posted at ~2400 rpm?

Regarding the "1 full turn = 8%"... 8% of what? That isn't a direct relation to my CO readings, is it?

Thanks again for the advice--

emcon5 · emcon5's Garage

Set the timing and idle speed. These are related, more so than idle mixture to idle speed. For 80-83 it should be 5º ±2º BTDC@ 950 RPM, vac hose disconnected, with max advance 21º ±2º BTDC @6000rpm, vac hose disconnected.

You can use a multimeter with a duty cycle guage to do a rough setting of the idle mixture. You want to set it as close to 50% duty cycle as possible (45 on a 4 cyl dwell meter, IIRC). Search the archives, I think the procedure has been covered in the past.

Make sure the engine is fully warmed up.

Tom

shrouded · 07-08-2004, 10:16 PM

Well, I am making progress getting this all figured out.

Looking at adjusting the mixture seems to be the most difficult for me. With my 3mm allen wrench I went fishing what should be the correct spot (as shown in the 101 projects book), but couldn't seem to find a screw back there. Was I missing it? Is there a trick for getting the wrench on there (since it was mostly a process of blindly groping behind the parts obscuring the area). Do I need an allen wrench much longer than my standard tools?

Doug Steinel · Doug Steinel's Garage

Shrouded, some cars have a cap covering the mixture screw. It must be removed. The long 3 MM with a handle that is sold to adjust the mixture is too long to get in there. Get a 3 MM "L" shaped allen about 4 inches long. Take the air cleaner off and seat the allen shining a flashligh to guide you. I just did this for the first time today. Richened up my mixture by turning the screw 1/16 inch clockwise and my car runs much better. I have an exhaust gas analyzer and supposedly my '82 should have the CO at no higher than .8. My cars runs horribly at that low a CO. I found it runs very well at 3%. Set it at .8 to pass the smog test and then richen it up when you get home. I'd curse the tree huggers but our host might just might be one.