Mike S

Here's where I'm at:

1987 Turbo
New Catalytic converter (SFR full exhaust)
MAP programmable fuel injection system
Danno's MAP chips for my TO4E
Wideband 02

15MPH - CO2 13.5% meas, 02 0.0% meas, HC 152ppm (max is 116), CO% 2.49 (max is 0.74), NO 1128 (max is 791)
25MPH - CO2 13.5% meas, 02 0.0% meas, HC 139ppm (max is 91), CO% 2.50 (max is 0.62), NO 1351 (max is 730)

I have the ability to tune the mixture in any zone and I have a wideband 02 so I really need to know what the ideal air/fuel ratio is for emissions. My wideband sensors tells me I'm around 14.7:1 air/fuel ratio at those speeds. Isn't this the ideal ratio? Am I running too rich still?

Mike S

I'm noticing that my 02 is 0, so from what I can tell that is a serious problem. How does the 944 introduce more 02 into the system. We don't have an EGR valve that I'm aware of.

Crazy Eddie

Jeeezzz
Mike I feel for you
Please forgive my ignorance
but did you consider replacing the maf with the stock air box and putting back your orig. chips ?
Here was my test in Feb.

Oh
I forgot these are the results
At this point my car is totally stock (engine wise)

15 MPH:
HC - measured = 35 max = 116
CO - measured = .17 max = .74
NO - measured = 226 max = 791

25 MPH:
HC - measured = 14 max = 91
CO - measured = .10 max = .62
NO - measured = 335 max = 730

Aleks951 Danno
Considering the hardships one has to go thru in this state to pass inspection,
what if we (Aleks, I and others want to upgrade our engines ie turbo wastgt
mass air, link 2, inject 55, etc. Could we theoretically just put back the stock
chips and pass inspection (maybe I should start a new thread on this topic?)
I would bet there has to be a s#$% load of people in this state that don't just use the cars on the track ..... if you know what I mean or un-install all
their mod they put on every two yrs .....
Thanks in advance
Regards
Ed

Jake951

Is your DME running closed loop with the stock O2 sensor and are you sure the O2 sensor is working? It's going to be very hard to pass a smog test if it's not.

special tool

Mike - what is your idle AFR? My idle is 20:1, and the car is very happy

Mike S

Well, sure enough I was running in closed loop mode? or is it open loop. I had unplugged it and wired in a resistor for tuning of the MAP kit. After plugging it back in I have verified that my 02 sensor is functioning.

Does the idle stabilizer valve add fresh air into the manifold at any point? I'm just wondering what else is turned off in clsoed loop mode?

Bill

Mike,

When the car is cold, the DME functions in "Open loop". In open loop (no feedback from the O2, sensor) the car runs rich, as a cold engine needs more fuel. To operate cold, the DME uses built in fuel/ignition maps to operate. This is neccessary because the O2 sensor will not provide feedback until it warms up. Once the O2 sensor warms up and starts to give the DME feedback, it goes into "Closed loop". In closed loop, the DME can make fine adjustments to the fuel/timing to get the mix as close to perfect exiting the exhaust pipe.

So there is nothing "turned off" as you say, just a warm up period for the O2 sensor.

Mike S

Hmm, that makes me wonder if this performance catalytic converter is up to the challenge. I can't seem to find any other explanation for the results.

Ben Z.

Isn't failing both HC and NO kind of strange? I thought that HC meant too much unburned fuel = too rich. And too much NO meant you were running too hot = maybe lean? I'm trying to learn about this stuff as I'll probably end up in some state with emissions testing later this year. Thanks.

Tom M'Guinn

Mike,

The smog limits for 87 and later cars are lower than for the 86 cars, even though the engines are virtually identical. Your State working for you! In closed loop, my car will bounce right around 14.7. I don't believe the car ever gets out of closed loop for the test, as they really don't put much of a load on it. As I mentioned before, I installed stock chips, injectors, fpr, intake, etc. for the test and it still did not pass by much. If you want to go that route, I'm happy to lend you whatever you might need -- expecially the adapter to put the stock intake on a big turbo. You must have found a friendly smog tester to run the test with a MAP set up and all.

Bill

No this is not strange. It is only strange in the context that a proper running engine will not have this condition.

You always must think globaly, as cars are not just pieces but systems. Installing just one piece, like a chip/injector/cat/turbo/air filter/etc, can and will affect an entire system. This is why I get so frustrated when people modify with a chip/injector/turbo/air filter/etc, impact an entire system, do not retune, and then blame/blast/lambaste the supplier. When in reality, the poor outcome is the installers lack of knowledge. But I digress.

Lets look at this senario. High HC.

This could mean that there is a problem with the air intake system. Possibly a clogged air filter and thus less air, same fuel, rich condition.

It could also mean a weak ignition system. Poor spark, incomplete combustion leaving unburned hydrocarbons, not a rich condition, but the same appearance and outcome.

Or incorrect feedback signal to the DME. Bad O2 sensor, telling the DME to richen mixture. Faulty engine temp sensor, telling DME to richen mix.

Ok so now you see cause. An how it can come from a multitude of places. Now lets look at affect. High NOX.

NOX is a byproduct from high combustion temps. As you state, a lean mix will cause high combustion temps and NOX. So how can an engine that is rich create NOX, since a rich engine typically runs cooler ? In the cat. The cat uses different metalic elements coupled with high temperatures, to continue the chemical reaction that cleans emmissions. This is why smog ***** always say to "make sure your cat is hot".

So in your senario, unburned HC is sent out the exhaust valve to the cat. Since there is an overabundant supply of hydrocarbons, and you have a hot cat, the HC ignites and is burned. The burning of the overabundant HC further increases the temperatues inside the cat. This abnormally high temperature condition inside the cat, creates NOX. But the cat is not designed to burn large quantitys of HC. Just clean up small amounts and get emissions as low as possible.

So now you have the senario, where at the tailpipe, you have high hc AND high nox.

.........and to the a$$clowns that blindly modify, stop bashing the suppliers that are putting forth the effort to supply us with goodies. Or our goodies will disappear.

DanD

Thanks Bill for the Dannoesk diatrab. Helps me understand the mess a bit more.

Mike,
I can't help much except to show you these pages I found on the internet. I did a search on...
ideal air fuel ratio for smog

And came up with this information about the 14.7 a/f..

http://www.anaheimrepair.com/news/article.php/12
Pollutants Produced by a Car Engine
In order to reduce emissions, modern car engines carefully control the amount of fuel they burn. They try to keep the air-to-fuel ratio very close to the stoichiometric point, which is the calculated ideal ratio of air to fuel. Theoretically, at this ratio, all of the fuel will be burned using all of the oxygen in the air. For gasoline, the stoichiometric ratio is about 14.7:1, meaning that for each pound of gasoline, 14.7 pounds of air will be burned. The fuel mixture actually varies from the ideal ratio quite a bit during driving. Sometimes the mixture can be lean (an air-to-fuel ratio higher than 14.7), and other times the mixture can be rich (an air-to-fuel ratio lower than 14.7).

http://www.babcox.com/editorial/cm/cm120230.htm

The ideal air/fuel ratio (called the stoichiometric ratio) for air and gasoline is 14.7 parts of air for every part of fuel. This ratio gives the best fuel economy and power, and produces the lowest emissions - just carbon dioxide (CO2) and water vapor (H2O).

-----------------------------------------

Assuming that he really is at 14.7 what else can he do to reduce emmisions?
I have heard that performance cats don't perform as well as stock cats.

Bill

DanD,

As I tried to explain, even a perfect fuel/air ratio can cause smog. It can appear rich, when the ignition system is weak. Also timing is important. The more advanced the timing, the LESS time there is to allow for complete combustion. Perfect air/fuel ratio, advanced timing, incomplete combustion, hydrocarbons in the cat.

What else can he do? He must go through the proper diagnostic proceedures to pinpoint the problem. An ignition scope is important. Also people on this board put too much stock in wide band O2 sensors. When tunning for emissions a four-gas analyzer is much better. Tailpipe readings are changed by the cat, so O2, and CO2 readings become more important.

Bolting on parts, then bringing the a/f ratio close to 14.7 to 1, to get power is somewhat easy. Getting these parts to meet strict emissions requirements...well we are finding out, is not so easy.

Tom M'Guinn

Random parts swapping until he passes.

Bill

Sell the 951 and buy an electric car.

Actually this is misstated. Sorry. A perfect a/f ratio will not appear rich. It will appear...well, perfect to the O2 or wide band. But because of incompete combustion, you send hc and Oxygen to the cat. That is why percents of O2 and CO2 are more telling about the combustion process.