Craig's 1987 Porsche 944 Turbo

IT PASSED!!

Yippee!! *:^) I got the car re-tested on 5/14/1999 after I adjusted the fuel mixture and timing via the rotary switch on the DME computer box. The various settings can be found on the Porsche 944 FAQ page (section 13.8), and I set it on setting #7 to get it to pass. That setting backs off the timing and makes the fuel mixture a little richer, both of which contribute to lower combustion temperatures and therefore lower NOx emissions (note, however, that as a result the HC and CO went up somewhat from the 5/3/1999 test, but they were still passing). You may notice that the car barely passed the 25mph NOx test (by a measly 4ppm), but at this point I'm just happy that it passed!!

I plan to post all the helpful and informative e-mail that I received from everyone on the Porsche 944 mailing list so that others may benefit from it.

Here's the info on the Virginia DEQ emissions testing for my 1987 Porsche 944 Turbo. For more info on the car itself, check here and read below. If you're interested, here's a link to my main home page.

Date	HC 15mph	CO 15mph	NOx 15mph	HC 25mph	CO 25mph	NOx 25mph
5/14/1999	78	0.29	692	98	0.54	1159
5/3/99	20	0.01	*2673*	28	0.01	*2094*
4/19/99	24	0.01	*2406*	33	0.02	*1918*
1/8/99	129	0.52	*2287*	124	0.65	*2193*
1/5/99	*226*	*3.56*	929	*163*	*3.75*	973
11/24/98	162	*3.42*	*1338*	157	*2.91*	*1601*
11/18/98	120	0.58	*1628*	86	0.53	*1230*
11/10/98	137	0.57	*2033*	131	0.7	*2027*
Average:	116.86	1.24	1899.14	103.14	1.22	1719.43
VA Standard	167	0.94	1273	162	1.04	1163

HC = Hydrocarbons, CO = Carbon Monoxide, NOx = Nitrogen Oxides.
The bold-italicized results indicate failures.

I live in Virginia, so the Virginia DEQ (Dept of Environmental Quality) standards apply. Here's what I did after each inspection attempt (best as I can remember):

Test Date	Action taken AFTER each test failure
11/10/98	After it failed, I got a somewhat "detuned" Stage 2 chip set from AutoThority. I believe they said that they backed off the timing somewhat
11/18/1998	After this failure I ran some "engine-cleaning" fuel additive through the system, which managed only to greatly raise the CO levels for the 11/24 test
11/24/1998	After the 11/24 failure, I replaced the Oxygen Sensor with a new one from Performance Products, which I was told (by several DEQ-certified technicians) was the most likely problem. I had to wait for the part to arrive, and being the "holiday season" and finals time for my last Master's class, I didn't have time to install the O2 sensor until just after New Year's.
1/5/1999	This failure is interesting, and greatly confused me. It appeared that the new O2 sensor "fixed" the NOx problem (this is the only test where NOx passed), but jacked up the CO and HC horribly!! First off, this was the only time I dropped the car off for inspection, so it was the only time the engine was completely "cold" when they started the test. I later learned that catalytic converters don't really "kick in" until the engine warms up (which explains the high HC and CO), and that NOx is formed under very high temperatures, which helps explains these test results. After the 1/5 failure, I ran some more decarbonizer through the gas...basically in desperation.
1/8/1999	I'm guessing that the reason why CO was high on this test is because I hadn't run out the tank of gas that had decarbonizer in it before I got it re-tested (oops). After this test, I took it to a local Porsche dealer for an "estimate"(HBL in Tysons Corner, VA), who said that the catalytic converter was "hollowed out" and needed to be replaced ($750 part, $284 labor (4 hours * $71/hour)), which would fix the NOx problem. Seeing their price as ridiculous (and already out $150 from the time for the "estimate"), I ordered a used catalytic converter for $175 from a place in California (w/ a 90-day guarantee), and replaced it myself (hence the long time between this test and the next one....took a while to find a used one, then I had to find time to install it).
4/19/1999	The impact of the new cat shows on this test. It greatly improved the readings on HC and CO (which had generally been passing, but barely). Unfortunately, the NOx reading remains basically unaffected, and way above the "standard." Nothing was done after this test except verifying that the O2 sensor was properly connected. Only reason I got it re-inspected on 5/3 was because you get a free re-test within 14 days...5/3 was 14 days after 4/19 - might as well use it even though nothing had changed
5/3/1999	After this test I asked for help on the Porsche 944 mailing list. Several people suggested that I adjust the rotary switch on the DME computer box to back off the timing and increase the fuel mixture. I did this (switch position #7) after the 5/3/1999 test.
5/14/1999	IT PASSED!!!!!!!!!!!!!!! LIFE IS GOOD!!! Based on the results, I'm guessing that the NOx stage of my catalytic converter is shot (or it's simply a two-stage) and that the AutoThority chips are also contributing to increased NOx. I'll deal with that in two years when it's time to test it again, but for now...IT PASSED!!!

Here are my only remaining thoughts on what could be causing it to fail emissions:

Take out the AutoThority chips entirely and re-install the factory originals. The problem is that although I have both of the original chips, they aren't labeled (except for a long number on each which is meaningless to me), so I don't know which one goes there. I plan to take them to AutoThority to see if they can determine which is DME, etc.
Could the brand new O2 sensor from Performance Products have gone bad or been bad to start with?!?
Since NOx forms at very high engine temperatures, could possibly replacing the thermostat with a lower temp thermostat help reduce NOx emissions?
I've read that there are "two-stage" and "three-stage" catalytic converters, and that the two-stage don't address NOx emissions. I've obviously got a two-stage since the new one drastically improved CO and HC but didn't affect NOx at all, so maybe I can replace it (again!) with a three-stage?!??!

I've also cleaned and re-oiled the K&N air filter, checked the spark plugs (brand new, properly gapped), and done anything else I can think of to fix it. I run only premium (usually 93octane) gas in it, and always buy from major suppliers (Exxon, Mobil, Texaco, etc), not convenient store-type stations, if it matters.

As you might guess, I'm extremely frustrated at this point - I've had this otherwise-wonderful car for over six months, but I've been unable to drive it (legally) for five months. I've spent about $600 so far, it still won't pass, and I'm running out of options. So far: $170 in a new O2 sensor, $175 in a new cat, $150 for a dealer estimate, and $80 in testing fees, not to mention my time spent installing stuff and taking the car for inspections and estimates. The most frustrating part is that although I've exceed the "emissions waiver" amount ($460), only the $150 at the dealer applies (because the money must be spent at a "DEQ-authorized repair facility" to qualify for waiver - which I call the "screw the home mechanic" clause).

On the bright side, I've learned a lot about emissions systems and testing....way more than I ever cared to know, actually. <smile> One of the best sources for info that I found was AutoSite. Their Auto Encyclopedia in particular is really nice, and has a great emissions section that cleared up a lot of confusion about why the test results came back as they did. BUT IT STILL WON'T PASS!!!

So, any ideas on how to fix my NOx emissions problem??? If so, please e-mail me at sccaldwell@mindspring.com and/or caldwell@uu.net

Here is a link to my Porsche page, in case you want to actually take a look at the car.

Craig's home page. Contact me via e-mail at home or at work.
Number of hits since 3/20/1999: FastCounter by LinkExchange