280 SE failed CA smog

[rumb]

Sadly it's not just CA.  Many states including Colorado have blanket adopted CA laws. Last year I sold 2 cars partly because of lack of smog equipment and I didnt want to be the one holding the empty bag.

[Feather535]

To update this story, I changed the spark plugs and that brought the CO down to 2%.  One of the 6 plugs looked pretty bad, so it's possible that cylinder wasn't firing consistently. 

After that I changed the engine oil, but that didn't result in a measurable improvement.

Next I'll replace the injectors and all the associated seals and o-rings.  This is because the engine won't idle if I try to lean the mixture out any more.  Even one marginal injector could cause this, so I'm hoping replacing them all will improve running enough to dial in that additional 1% reduction.

[daantjie]

Man, after all this you will have the cleanest running 116 in all of Cali.  Ah - nold will be proud of you

[Feather535]

Since my last post I've changed the oil, replaced the spark plugs and the injectors.  CO is still in the 2-3% range.  The engine runs strong and idles well at that setting, and that seems to be where it wants to be.  If I lean the mixture out any more, it won't idle.  At this point I don't know what to do next. 

This brings me back to thinking about the cat.  Maybe 3% is where this system wants to run and it depends on the cat to clean it up the rest of the way?  The factory manual mentions testing somewhere upstream of the cat, so comparing that reading and the tailpipe, where I have been testing should indicate whether the cat is working.  Just need to find that test port, which looks like it's somewhere on top of the exhaust manifold.

[Alec300SD]

The auxillary air valve may not be fully closing and/or its rubber hoses may be deteriorated.
BTDT on my prior '79 245DL Volvo wagon.

[revilla]

Timing. I'm guessing you have already done that. If not, rotate the  distributor and using a stroboscopic lamp see what effect that has on CO levels. As a starting point set it up to zero. Then move from there. You'll need to readjust the mixture and idle nylon screw with each distributor rotation/adjustment.

[rumb]

What thermostat is in the car?  Maybe put a higher temp one in?

[Feather535]

The auxillary air valve may not be fully closing and/or its rubber hoses may be deteriorated.

Ugh! The auxiliary air valve is even less accessible than the WUR...but the big hose going to it is the only one on the car that looks suspect, so it's worth a look. 

[Feather535]

Timing. I'm guessing you have already done that.

I have done this.  Timing between the range of 10 degrees BTDC and 10 ATDC doesn't have much effect on CO.

[revilla]

Hi, It depends on what's your goal. If you're aiming to setup the engine "by the book" and obtain an optimal performance on a 45YO engine, yes setting up the timing using the manual might get you there or close enough. But if your objective is to pass the emissions test, then we need to park the theory/book for a moment. I thought the ladder was your goal. If not, my apologies.
Yes, advancing the ignition timing will lean out the mixture, to a point. Retarding it has the opposite effect.  You want to lean out the mixture which will reduce your CO%.  You're not far from the target, I was simply suggesting a way (an old trick actually) to pass your test. But again if your goal is to setup the engine by the figures I'm afraid both objectives might not be compatible in an engine that old with other root causes hanging around (e.g. unmetered air ingress, worn valves, etc). It's your car thus your choice.

The key is to find that sweet spot of timing+mixture+idle to reach the CO target. Simply rotating the distributor and reading CO won't cut it. Try advancing it to -10, -15... and compensating the RPMs changes with your idle screw then re-adjusting the mixture hex screw systematically. You will see an effect on CO as you're playing with the volume of burnt/unburnt fuel and the sniffer in the tailpipe will certainly capture that.
Good luck.

[rumb]

maybe try snake oil?

https://www.holtsauto.com/redex/products/redex-petrol-pre-mot/

[Feather535]

It depends on what's your goal. If you're aiming to setup the engine "by the book" and obtain an optimal performance on a 45YO engine, yes setting up the timing using the manual might get you there or close enough. But if your objective is to pass the emissions test, then we need to park the theory/book for a moment.

I set it "by the book" originally, but you are right: now I only want to pass the test, knowing that performance might be less than optimal.  So I haven't yet tried what you suggested, adjusting timing, mixture and idle speed simultaneously to see if that affects CO.  I'll try it and report back.

[ramiro]

I still think that the main problem is the cat after all the idling and trying to get it running it must be burned free , but i also don't know how if you cant drive on the road.

2-3 % should mean that you can't higher then 13.8 afr , the last 280 i was adjusting had no problem idling at 15 - 16 afr (less than 0.1% co) wasn't smooth but had no problems idling.
Also i got 0,3 % co without even specially adjusting anything and also without any cat on my 6.9 .

So it would make sense that the cat is full with unburnt stuff that is slowy burning off and changing you co.

[Feather535]

I'm beginning to think ramiro is on the right track.  Adjusting the mixture screw affects on engine performance (too lean and it won't idle and is hard to restart), but it doesn't have a significant effect on CO.  This happens even with the iterative process involving timing, mixture and idle adjustments that revilla described.  So it looks like something besides fuel mixture is influencing CO at the tailpipe.  What could it be?

[rumb]

https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Kinetics/07%3A_Case_Studies-_Kinetics/7.01%3A_Catalytic_Converters

Perhaps your cat is in need of replacement?

https://www.autozone.com/emission-control-and-exhaust/catalytic-converter

Lucky you - you need the CARB approved one in CA.