924Board.org

[Conrad]

I am new to the board, but have been observing it occasionally. There is a lot of very useful and helpful information here, thanks everyone.

I have a 1980 N.A. (date of manufacture June 1980, engine number VCxxxxx) It's a one-owner Arizona vehicle which seems reasonably well maintained but with a lot of miles.

When I first went through the emissions test last December, I put in new plugs, fuel filter, air filter, and set the ignition timing. The timing spec for the 1980 is 0 deg (TDC) at 950 rpm with all vacuum hoses connected. I had some trouble finding the faint timing mark, but eventually found it by turning the engine to TDC, lining up the dot on the cam wheel with the pointer on the cover. Thanks for the picture posted by someone on this board. I also learned from previous owner's mechanic how to adjust the mixture at the air flow sensor, using a 3 mm allen wrench. Said mechanic had left the adjustment hole open, so I plugged it. For the idle speed I used the dashboard tach. The idle drifts up and down by 100 rpm. The oxygen sensor was disconnected long ago. The catalytic converter is present, but old. I got a new fuel filler cap, because they pressure test it, and changed the oil, which might have a small effect on the hydrocarbons.

To my surprise, the ignition timing was about 3 deg off. It seemed to be set to a hand-scratched mark on the flywheel. This might have been an attempt to wring more performance out of the engine, essentially reverting to earlier timing specs. I may also have a 1979 or earlier distributor installed, does anyone know how to tell ?

So I set the timing to 0 deg, leaned out the mixture a tad, and went for the emisssions inspection. The inspectors were intensely interested in looking under the hood, and even called over the supervisor. But the verdict was "you pass." The test report showed readings at idle and cruise as zero, which can't possibly be right, but I wasn't about to ask for a retest! Unfortunately that means I have no real information on how close I came.

While setting the timing, I tried disconnecting the vacuum hoses temporarily from the distributor. Neither had any effect on the timing at idle, and neither seemed to have any negative pressure in the hose at idle. I didn't worry about it much, because I had passed the inspection.

Now it is time for emissions again (only 7 months and about 200 miles later). I replaced a few old looking vacuum hoses. One 9mm hose which connects to an air valve near the accelerator cable was split at the end and patched with duct tape, and connected to a plastic tee-joint with one end blocked. I also discovered that the 3.5 mm hose from the retard side of the distributor was plugged with a metal slug, very close to the distributor end !! With a new hose, the retard side now has strong negative pressure at idle. When connected to the distributor, it does change the idle timing. From a vacuum hose diagram in the engine compartment, it seems that the same hose "should" go from the distributor to a temperature sensitive vacuum switch located on a brass coolant pipe at the back of the engine, before going to the manifold. Since that vacuum switch seems always to be open, I bypassed it for now. Does anyone know if this switch should open or close as the engine warms up ?

So now I have reset the timing to 0 deg TDC with the new vacuum hose connected. The performance coming off idle seems better than before, both with no load and while driving. My question is, I passed before, but now I have changed timing curve, so will I flunk this time ? That would be ironic, because I am gradually bringing the car closer to specs. The plug in the vacuum hose could have been a mistake, if someone plugged it while disconnected for testing and then forgot, or more likely another attempt to undo perceived factory "detuning." The car was serviced by the same mechanic for many years. Has anyone heard of a "retuning" combination involving a change of about 3 deg to the idle timing, disabling the vacuum retard line, and possibly an early distributor ?

Arizona runs a "short test" on 1980 and older vehicles, which does not measure nitrogen oxides. They have been getting stricter on the "visual" inspection for "tampering," so maybe I will connect that vacuum switch after all.
_________________
1980 924 N.A.

[Smoothie]

As far as I can tell, a US '80 NA should have 2 vacuum switches (vacuum valves) side-by-side on that coolant pipe. If you have EGR, one of those switches should be to control that - delaying EGR operation until after the engine's warm. The other vacuum switch should be to delay purging of the charcoal canister also until after the engine is warm. -Both should be closed when cold and open on warming.

You're in a better situation than me for passing emissions - I get tested for NOx, so have to achieve a fine balance between too rich and too lean. 2 years ago I had to finally unplug the o2 sensor to get it through (3-4 inspection tries), while this year (3 times through the line) it wouldn't pass until I reconnected it, then passed the NOx test by a slim 10 (measured 1313 with a max limit of 1323). If you fail for CO/HC, all you need to do is adjust more to the lean side without worrying about the NOx level. -But of course watch that you don't go so lean as to overheat the exhaust side..
Incidentally, EGR cools combustion, reduces knock and lowers NOx oddly enough by feeding some exhaust back through the intake.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Conrad]

Fortunately, my car does not have EGR. There are indeed two switches on the coolant pipe, but one is a vacuum valve and the other seems to be electrical. The electrical one is also disconnected. The vacuum hose diagram pasted to the driver's side front of the engine compartment appears to show a pipe and a vacuum valve between the distributor and a source of vacuum such as the manifold or "plenum chamber" The vacuum valve on the pipe is presently stuck open at all engine temperatures. I may connect the valve in series before I go to the inspection station, even though it will have no effect, just to keep the inspectors happy. Last time three of them stood around for 5 minutes looking at the engine. If the vacuum valve is indeed part of the evap system, I certainly don't want to create the impression of creative hose routing.
_________________
1980 924 N.A.

[joedeats]

emissions what are emissions? poor smog nazi state guys.....man i love florida.......
_________________
"Sabres out! Sabres Ready! we got hippies to ride down lads!"

Will the last rational adult to leave Mexifornia please turn out the lights.

[augidog]

Take out your air filter before you go through the line.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

[Conrad]

"emissions what are emissions? "

Arizona only tests in the Tucson and Phoenix metro areas. And the people who live outside sometimes remove all the emissions equipment on their vehicles. Then they move to the city to get a job, and... Let me put it this way, you see a lot of '70s and '80s pickup trucks and big cars for sale cheap.

So, mine passed, here are the numbers:
idle cruise (25 mph in 3rd) max allowed
HC 110 ppm 99 ppm 220 ppm
CO 0.31% 0.23% 1.20%

I set the idle mixture about one-twentieth of a full turn CCW from best running.
_________________
1980 924 N.A.