1983 911SC Federal Emissions (49 State car)

[porschedude996]

Hello, I’ve been working towards getting my car project on the road and having problems with Hydrocarbon value at idle.

Some history:

Purchased last year and has a Nevada Title. Many of the vacuum lines were toast from the desert. Without dropping the engine I managed to get the lines sorted out. What a bi1@h getting to the vacuum lines behind the air-box. I performed a complete tuneup, replaced the injectors and O-rings, plugs, wires, rebuilt distributor, O2 sensor, DEC 49 state bill catalytic converter, replaced the thermal time switch, etc.

I had the smog check performed all but the idle HC passed. HC at idle is 502ppm. Max is 120ppm.

Anyone have a guess as to what can be the culprit?

[Targa Me]

Here's a few things I do to help pass the smog check. Along with everything else you did.
1. Change the oil and filter. Dirty oil can lead to higher HCs.
2. Clean all the breather hoses. Those hose have oil residue.
3. Inflate your rear tires to the max psi. For my rear tires it's 44 psi. This will reduce the load on the engine as they test.
Good luck.
Larry

[Bill Verburg]

Originally Posted by porschedude996

Hello, I’ve been working towards getting my car project on the road and having problems with Hydrocarbon value at idle.

Some history:

Purchased last year and has a Nevada Title. Many of the vacuum lines were toast from the desert. Without dropping the engine I managed to get the lines sorted out. What a bi1@h getting to the vacuum lines behind the air-box. I performed a complete tuneup, replaced the injectors and O-rings, plugs, wires, rebuilt distributor, O2 sensor, DEC 49 state bill catalytic converter, replaced the thermal time switch, etc.

I had the smog check performed all but the idle HC passed. HC at idle is 502ppm. Max is 120ppm.

Anyone have a guess as to what can be the culprit?

HC is the result of incomplete combustion and can come from too much spark advance or mixtures that are too rich or too lean but

w/ close to 150k on the clock I'd guess that the rings or valve guides are the source of the excess HC

[Targa Me]

Originally Posted by Bill Verburg

HC is the result of incomplete combustion and can come from too much spark advance or mixtures that are too rich or too lean but

w/ close to 150k on the clock I'd guess that the rings or valve guides are the source of the excess HC

Maybe a compression check and leak-down check is in order.
My '84 3.2 just passed its smog test this past weekend. I have 392,920 miles on the original engine.

[proporsche]

hmm 0.08 on Co ..seems a little too lean..i would try to rich it up...and try to find place where you can test the emission without official smog station
Ivan

[EC900]

How was she running otherwise before the tune? And after?
2¢ = Maybe proper spark plug and gap? Also wondering if vac leak was created when trying to replace lines behind air box.

[ahh911]

HC falls by over 5 times at 2500 rpm, from 500 to 70 ppm, still think it's rings?
Idle O2, 0.5 ppm
2500rpm 02, 0.2 ppm

Oxygen is going up at idle.

Exhaust leak, or O2 sensor duty cycle out of range at idle. Did you check the FV duty at idle is within range, 45-65%? 45$ oscilloscope from Amazon. Check for exhaust leaks before the O2 sensor. Those are my guesses from your data, but it is my first time looking at this sort of thing. I assume the O2 sensor stayed connected during the emission test?



You've added egr because the 49 stater is moved to CA? Maybe an air leak? You've got a cat, I don't know if it removes the CO more effectively than HC when the O2 sensor drives it rich. Because from this curve (no cat in this curver) the CO and HC would go up together if driven rich by lambda unit. Your CO is low as pro_p pointed out.

[ahh911]

If your O2 sensor isn't working than Ivan (p_porsche) explanation of too lean would be correct.

Buy the oscilliscope shown, you can add a 6 battery holder and zip tie it to the device to make it portable. When the batteries dim, the thin goes nuts, so replace them.

Added blue to show lean. This would be a lean setup and O2 sensor inoperable or again out of range.

[porschedude996]

Originally Posted by ahh911

If your O2 sensor isn't working than Ivan (p_porsche) explanation of too lean would be correct.

Buy the oscilliscope shown, you can add a 6 battery holder and zip tie it to the device to make it portable. When the batteries dim, the thin goes nuts, so replace them.

Added blue to show lean. This would be a lean setup and O2 sensor inoperable or again out of range.

I bought a little o-scope and it worked for a few minutes...another story...

I have a new different model coming and will try it out.

Given the place that the car lived, Las Vegas, and as old as it is, I'm thinking manifold boots. I also ordered a smoke tester.

I'll check back in when I get back to it.

Tnanks all!

[porschedude996]

Update 02/16/2023:

Previously: tune up, plugs, wires, oil & filter change, valve adjustment, vacuum lines sorted out, injector seals, rebuilt distributor, checked fuel pressures, decay checked, exhaust gaskets, new CAT, O2 sensor, fuel filter, accumulator, thermo-time switch, oil temp switch (rt cam cover), checked AFR fwd of CAT, checked CO before Cat using old 1980’s tester (didn’t like results). Removed and bench tested AAR, AAV, Decel valve. AAR was and then wasn’t working, disassembled, cleaned, and adjusted.

In place tested the WUR, tested well using the FI gage set.

Didn’t test leak-down or compression.


Upon completion of the above, I failed with 502 ppm hydrocarbons at idle. CO looks really low, but it’s post CAT.

More Recent Testing and Investigation:

1. Smoke test shows a couple of wisps out the corner of the air filter. No big deal there.
2. New O-scope ($100) works well. Much more stable and intuitive than the $50 one
3. New distributor with working ignition retard function. With initial at 5 degrees BTDC, with the retard signal, it drops to 5 degrees ATDC. I do think there is something about this based on my previous experience on an old vehicle where nothing but the backing off the initial of 5 degrees BTDC to O degrees reduced the hydrocarbons at idle. Why else would Porsche add the retard feature unless it was to pass Fed & State Emissions.
4. Bought a CO Gas Meter (Gunson). Measured CO after CAT trying to use data from the first Emissions Test.
5. Decided to do something a little unorthodox and tested post cat using pass/fail criteria from CARB and Frequently Valve readings and the CO meter. Adjusted idle mixture to 49-52 duty cycle and monitor the CO. My setup shows the FV is called upon to a happy value. CO I measured using my (Gunson) was .6%.

Well it worked! I passed the emissions test.


I do think i’m still running too lean. Small surge during cold start, but runs great once warmed up. Road test seems good, engine behaves as it should (a perfect gentleman).

I now have a registered vehicle with license plates and title coming. This was my primary focus to get over the ownership thing.

Next is to test the Pre-CAT CO and look at the Air-Fuel Ratio.

[AndrewCologne]

3. New distributor with working ignition retard function. With initial at 5 degrees BTDC, with the retard signal, it drops to 5 degrees ATDC. I do think there is something about this based on my previous experience on an old vehicle where nothing but the backing off the initial of 5 degrees BTDC to O degrees reduced the hydrocarbons at idle. Why else would Porsche add the retard feature unless it was to pass Fed & State Emissions.

Beside lowering HC output at combustion the ignition retard while idling also provides a much higher exhaust flow temperature which keeps the original non heated 1-wire sensor at high temps which makes it reacting faster and by this working better.

[ahh911]

Good to hear.

Seeing how the O2 dropped by a factor of five, I'd say it was pretty clearly running lean before the O2 and frequency valve were setup correctly at idle. I doubt the retard had much to do with the results, you can unplug the vacuum line and test once warm. The FV should stay in the 50% range, but you could keep an eye out on that during the test.
Phil