I've searched briefly through the forum, but would also love some advice for a 928 owner who's never been through a smog test.

So anyone out there with some helpful knowledge?

Thank you in advance!

Vinh

 

If your car is stock, in good tune, a USA model, and previously registered in Calif, no worries.

Look at the top of your registration to see if you can go to any type of smog check place or if you are restricted to a "Test only" station. Find a coupon from the PennySaver or other coupon source, and locate the nearest smog check station of your "type", call to see if they accept or match other coupons, and run it through. Test only tends to run a bit more, and the reason for a coupon and checking prices is that prices vary from about $40 (including $8 for cert) to $75 or more, and the results are the same.

If the car was never registered in Calif, smog check may still be the same, but you may get zapped with some extra DMV fees.

Avoid the non DMV service for a fee places, and avoid the DMV if you have AAA or equivalent.

Drive it some, use fresh gas, but otherwise nothing special really.

If you have anything funny with your car, maybe pick a small place at a busy time.

 

http://www.smogtips.com/smog_coupons.cfm
I've used this for many years and suggest testing your O2 sensor first, that's an easy fail point.

 

I am in Texas, but here is a hopefully useful bit of information.

My car recently failed the low speed portion of emissions testing (15 mph) but passed everything else on the test with flying colors which consisted of reving the car in nuetral to some RPM and then a 25 mph test. The technician was a really nice guy and told me to go drive the car and get the cats nice and toasty and come back. I did this, and the car was still just barely failing on the low speed. At 15 mph on the rollers in top gear, the car was basically idling. So I asked him to shift into a lower gear in order to get the car off the idle switch. And what do you know, the Nox went from about 1250 ppm to 600 ppm just by opening the throttle a little and letting the sensors do their thing. The limit (in Texas) for my year car (87) was somewhere around 1050 ppm for Nox.

I am only guessing as to why this helped but I think at idle, with the idle switch activated, the car is using a pre-programmed map, and ignoring the O2 sensor. Opening the throttle, and therefore breaking the contact on the idle switch, let the car adjust the fuel mixture properly, and the car passed easily.

Edit:

I just realized that high Nox is a product (usually) of high combustion chamber temperatures. Although my ignition timing is stock and has not been altered, my cam timing has. I advanced my cams a couple of years ago around 4 degrees on one bank, and 6 degrees on the other, and this could be causing the high Nox reading. Extra un-metered air will also cause a high Nox reading, but I don't think I have that problem. So I'm not sure why opening the throttle had such and effect, but it did.

 

It's no different that any other 1976+ year car.

'89 S4 GP White/Black
'76 912E Silver/Black sunroof

 

The dirty trick is to top up the tank with 1-2 gallons of E85 before smog testing, makes the test person scratch his head

 

Hey Everyone, thanks! I love this forum! I'm going to go into AAA and have them test it, it passed two years ago in California, so I don't think there should be anything to worry about.

Thanks again,

Vinh