Failed smog for NOx

[Kurt B]

all other readings were good. Failed at "15mph".

Anyone have similar experience. Ca smog stuff.

Got CAT put on and all of that. It's chipped, but it passed chipped before.

Suggests "air pump" and timing in the hand out they give.
EGR...whatever that is. Failing smog is a no win for the do-it-yourselfer unless you have a whiffer, and I don't.
looks like a wrench will have to get it so I pass,but I'm open to suggestions.

[Doug Zielke]

Well, your 3.2 certainly doesn't have an air pump, nor EGR.
If the cat and O2 sensor are functional, the NOx should be under control.
Also, very, very lean mixtures will cause high NOx readings.

[HarryD]

Originally posted by Kurt B
all other readings were good. Failed at "15mph".

Anyone have similar experience. Ca smog stuff.

Got CAT put on and all of that. It's chipped, but it passed chipped before.

Suggests "air pump" and timing in the hand out they give.
EGR...whatever that is. Failing smog is a no win for the do-it-yourselfer unless you have a whiffer, and I don't.
looks like a wrench will have to get it so I pass,but I'm open to suggestions.

Hmmm.... NOx is made in the cylinder at high temperatures. Per my understanding of combution, higher temperature, the more NOx is made. This happens because the nitrogen in the air (air is 78% nitrogen) combines with the Oxygen instead of burning the fuel. To lower the peak combustion temperature, car makers return some of the exhaust gases to the cylinder [E(xhaust) G(as) R(ecirculation)]. This slows down the formation of NOx but reduces the power since you displace fuel and air with exhaust gases.

So..... The air pump may help since this adds air to the exhaust and dilutes the gases.

Timing may be more significant since it will affect how long the actual burn time is since the fire will not start until the spark is issued. A late spark should lower the NOx but increase the CO and HCs.

As stated above, if you richen the mixture, you should lower the peak flame temerature and reduce NOx but you will have higher CO and HC's

Turns out you have to balance all three to get ok.

Good luck.

[makaio]

Kurt, I'm sure you did, but I have to ask... ... was the engine nice and warm before the test?

[motion]

Kurt.. mine failed nox last time too. Replaced the cat and it was fine.

[HarryD]

Originally posted by motion
Kurt.. mine failed nox last time too. Replaced the cat and it was fine.

Makes sense, assuming you have a "3-way" cat it should be converting NOx to nitrogen and oxygen, CO to CO2 and HC to CO2 and water.

[Tyson Schmidt]

It's your own fault. You should have studied more.

[Kurt B]

Okay, so if I had put on my CAT, forgot the upper gasket on the cat (for the driver's side bank of exhaust I think), didn't really bolt it on too tight 'cause I was planning on taking it right off after the whiff check, hand tightend the O2 sensor into it...could THAT have caused it? The CAT is fine. It's been in my shed since the last inspection where it was on the car for around 3 days prior and was brand new at the time.

Also, it says on list of possible problems "too low Octane"...
What if I put in 91 as per usual and like 3 cans of octane booster in the tank, then took it down? Running like 100 octane ....

I tightened up the cat and will replace the lost gasket (found on driveway) then was thinking of going back.

I have to go to a test only center, and I just did smog last year--only supposed to go every two years. But on the top of the sheet it says

"Inspection Reason: High Emitter Profile"
Aholes.

[studeb]

Post all the numbers, its easier to work things out.
If your cat is good it should bring NOx down. O2 sensor must be connected for cat to work properly.
Higher compression due to carbon build up also boosts NOx
You can also take it a garage and have them pre-run it for you, then go to test only for real test.
Also when it fails, only "smog certified technicians" are supposed to work on the car.

[Kurt B]

Thanks Steve W and stude...but I can't put the old chip back in. The W is soldered in there. I had to desolder the original...um..I gotta pass with it. I'll just have to go to the wrench---Explains why my fuel consumption sucks. I am going to try to see what I can do with the Fuel Quality Switch to 4. What does that FQS do? I hope there is a diagram in Bentley...

[Steve W]

I would seriously consider desoldering and putting a socket in there to do chip swaps. Use a cheap solder sucker from ratshack. You will have this problem again two years from now again. Cheaper than visiting a wrench. Position 4 leans the mixture by 4-6%. You can smell it right away. Do a search for FQS or Fuel quality switch on this board, and you'll find multiple posts on the different settings.

[Kurt B]

Sounds like a weekend project. Without beating the issue to death, I'm going to post my actual numbers to glean any more information if possible.
15MPH = 1494 RPM CO2 = 11.6% O2 = 4.5%
25MPH = 2403 RPM CO2 = 12.8% O2 = 3.3%

HC (PPM)
15MPH MAX: 138 AVE: 41 MYCAR: 80
25 MPH MAX: 113 AVE: 29 MYCAR: 39

CO%
15MPH MAX: .85 AVE: .13 MYCAR: .32
25MPH MAX: .65 AVE: .11 MYCAR .04

NO(PPM)
15MPH MAX: 1148 AVE: 399 MYCAR: 1305
25MPH MAX: 978 AVE: 332 MYCAR: 977

Key points: really pushing the line for NO. However, my CO% is very low at 25MPH--It is .04 when the AVE is .11.
So..how are CO and NO related is a question...

[Steve W]

Kurt, this may help - from Bosch Fuel Injection & Engine Management:

[studeb]

Originally posted by Kurt B
I'm going to post my actual numbers to glean any more information if possible.
15MPH = 1494 RPM CO2 = 11.6% O2 = 4.5%
25MPH = 2403 RPM CO2 = 12.8% O2 = 3.3%

HC (PPM)
15MPH MAX: 138 AVE: 41 MYCAR: 80
25 MPH MAX: 113 AVE: 29 MYCAR: 39

CO%
15MPH MAX: .85 AVE: .13 MYCAR: .32
25MPH MAX: .65 AVE: .11 MYCAR .04

NO(PPM)
15MPH MAX: 1148 AVE: 399 MYCAR: 1305
25MPH MAX: 978 AVE: 332 MYCAR: 977

Key points: really pushing the line for NO. However, my CO% is very low at 25MPH--It is .04 when the AVE is .11.
So..how are CO and NO related is a question...

I don't have my notes here, so this is off the top of my head. Either you car is running lean, you have an weak air pump or you have a miss in one cylinder. O2 should be les than 1% .
Check for a vacumn leak. A richer mix should also cool the chamber, which could bring NO down also.
CO2 is also low.

[Rick Lee]

Anyone have a photo of the fuel quailty switch? I'm having big rich mixture problems and it has the wrench stumped. I'm really getting desperate and will try just about anything now. I'll try to remember to get my numbers and post them tomorrow.

[steve911]

Kurt-
I gleaned this from the shop that did my smog last week: be sure the tech doing the test knows about Porsches. Apparently the very last test done has to be done VERY carefully, otherwise the fail test.

When they bring the RPMS from 3-4000 down to idle, THEY HAVE TO DO IT GRADUALLY, otherwise the system fails the car. My guy said that they learned this the hard way several years ago when almost every P-car they did failed the last test.

I'm no engineer, so I can't vouch for what is happening, but that's what he told me and my '85 passed, so I'm happy.

YMMV

[Doug Zielke]

Originally posted by studeb
....you have an weak air pump ......

The 3.2's don't have any "air pumps".

[Kurt B]

There's something big under my right rear fender wedged up in there. It's connected to the vacuum lines running around the engine. I asked before if anyone knew...
Big cylinder wedged under right rear fender with a couple of vacuum lines running to it...

[Rick Lee]

You're joking, right? Kurt, I know you know that's your ext. oil thermostat.

[HarryD]

Originally posted by Kurt B
There's something big under my right rear fender wedged up in there. It's connected to the vacuum lines running around the engine. I asked before if anyone knew...
Big cylinder wedged under right rear fender with a couple of vacuum lines running to it...

Carbon canister maybe? Mine looks like a muffler in the trunk but according to the PET yours is a cylinder and is not in the front.