I had posted about a month ago concerning things that I could do to pass a failing emissions test. I passed on HC and CO, but failed on NOx. Well, I just went through my re-test and passed!! I'd like to share my data.

I tried doing my due diligence to find vacuum leaks but none surfaced, checked some of the other usual suspects and found nothing out of the ordinary. For fear of failing the free re-test, after which I would have to pay another $50 to test again, I decided to take some advice given in my previous post...

I plugged the vacuum hose that goes from the intake manifold to the ignition module with a small screw which, I was told, would make the ignition system default to a pre-programmed "lean" mode.

Below is my before and after data:

Before
HC: 1.96 Limit: 2.25
CO: 12.65 Limit: 23.74
NOx: 4.28 Limit: 3.25

After
HC: 2.14 Limit: 2.25 **close**
CO: 16.72 Limit: 23.74
NOx: 2.29 Limit:3.25

Thanks to Kane and gt6 for the good advice.

Bean
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'80 242GT 91k, '94 945T 110k

This kind of information is rare, as most of us when faced with a "fine" as that $50 retest certainly is, will do everything rather than just one thing, making it really difficult to know what one thing was the major influence.
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Art Benstein near Baltimore

I figured that some people might find it interesting. It sure was easier to plug that hose than it would be to retard my timing.

The only things that I did to the car before the re-test:
- New L/F ball joint
- Installed some sheet metal (aluminum flashing) under the right rear passenger foot well to cover (sorry, reinforce) the rusted areas. Liberal use of undercoating helped make the job look professional.
- Filled my gas tank.
- Washed the front and rear windows

My biggest concern was how the other two, passing, gases would react to the screw-in-the-hose trick. I was psyched to see that they stayed in spec, the HC just barely!

While on the same thread...the car seems to have the same amount of power as it did before. Any reason not to keep the screw in there?

Bean

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'80 242GT 92k, '94 945T 123k

Glad the trick worked for you.

You will certainly not harm anything by driving around with the default ignition advance, but I know that my 240 has significantly more power with the line connected properly.
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Speed Racer, '83 240 R, '74 164 E, '93 940 OL1 (Manchester, CT)

>- Filled my gas tank.

Aha!

Did you put premium in it or maybe a pint of alcohol? I've heard those are tricks to slow down the burn and reduce NOx.

>Any reason not to keep the screw in there?

It is hard to disagree with anecdote. I don't know.

But I can tell you have a safer brick with the body patched and the ball joint replaced.

Sometimes I wish I had the emissions testing facility all to myself for a day. Or could hang out with the "little man behind the curtain"--;-)
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Art Benstein near Baltimore