pappy92651

Take a look at the attached chart. I'm failing NOx (typical). I can adjust fuel pressure up to almost pass but I can't quite get there. I have custom AT chips in the LH and they will be removed next to retard the timing. The entire exhaust is new. Everthing is perfect except for NOx. Suggestions?

worf928

High NOx can be a symptom of lean running. Dirty injectors with poor spray pattern leading to a lean cylinder or two? Have your injectors ever been cleaned? Run Techron through every once in a while?

perrys4

I almost failed due to nox and the suggestion seemed to be the O2 sensor.....Nobody seemed to have a definate answer. I think Devek recommended this. Should be in the archives

perrys4

I just did a search and a thread Jserio started had a member that failed NOX and he replaced his O2 sensor and his results were dramatic. He has his tests posted so you can see the difference.

pappy92651

Guys,

Thanks for the response. The injectors were replaced in 2002 but they could be fouled (possible). I replaced the O2 sensor, fuel pumps, filters, engine oil, air pump filter, air filter, CATs, and checked all vacuum lines. Suspects are injectors, MAF, chips, spark plugs, and the LH brain. With the fuel pressure at 58 PSI my NOx numbers were 609 and 997 ppm (close to passing). I'm thinking of changing a combination of things that you mentioned. Someone else PM'd me on fuel additives / mixture. We shall see. I think the new high flow exhaust has a lot to do with this. It might prompt me to install the new intake manifold if I have to I tear out all the other stuff.

perrys4

Pappy, Greg told me a story where they couldnt get a car to pass and they ended up replacing virtually everything with new parts and it still failed. They took off the parts and put the old ones back on since it didnt work and then Ken got the idea to take it to a different test station and it passed! Seemed the stations arent all calibrated the same.

pappy92651

Hello Ron,

Greg told me that same story. I'm going to EZ Smog tomorrow. My car passed twice there. We shall see. I'm still going to change the chips out before I go.

If nothing works Greg will have my car until it finally passes.

Ken was nearing a highly explosive moment (match and gasoline)!!!

Glenn Evans

High NOx and very low CO readings indicate that your engine is running lean. Have you checked for vacuum leaks?

SharkSkin

If you want a quick fix that will reduce combustion temps & NOX try water injection for the test. You could flush your windshield washer system, fill it with distilled water, and run a sprayer into the intake. When you get to the smog place, jumper the washer pump to run when the car is running.

jserio

Hey Pap, You could try +4 plugs and removing the chips. The cooler burning plugs and the factor chips oughta thicken the mixture a tad. I heard the Platinum +4 fire on the cooler side. Do this and the go for a pre-test. If your still high then cats may be to blame but I believe you have the high flow cats on there and not factory. Cheap check so give it a shot.

ROG100

On my GTS I had the same problem - tried everything - O2 sensor, plugs, cats - in the end it was the MAF - changed that and passed.
Roger

WallyP

NOx is produced when combustion chamber temps exceed 2300 deg F. This is the only major factor in NOx production.

There are two strategies to reduce NOx output:
- Reduce combustion chamber temps, normally thru the use of exhaust gas recirculation(EGR), ignition timing, etc.
- Reduce NOx in a three-way cat. The fuel/air ratio must be very near stoichiometric for the cat to function properly, and there must be excess air in the cat - i.e., the air pump must be working in most cases. There are three-way cats that will function (at a less-efficent level) with no air injection.

Since your car doesn't use EGR, the only thing that you can do to reduce combustion chamber temps is to replace the standard chips to bring the ignition timing back to stock.

The only other major factors should be:
- Correct (i.e., three-way) cats installed.
- Air injection to cats working.
- Mixture controlled to stoichiometric.

The hot or cold ratings for spark plugs refer only to the mean temperature of the tip of the plug while operating. There is no effect on the combustion temps, unless the plug gets hot enough to cause preignition, or fouled enough to cause misfiring.

Lorenfb

"Since your car doesn't use EGR, the only thing that you can do to reduce combustion chamber temps is to replace the standard chips to bring the ignition timing back to stock." - WallyP -

This is probably the biggest factor in reducing the NOx on an engine where all
other elements are O.K.:

1. a good CAT
2. proper fuel pressure
3. a good MAF sensor (fairly problematic)
4. a good O2 sensor
5. a good LH control unit (properly affected by O2 & MAF sensor)
6. good LH & EZK system grounds & powers
7. proper engine temp, e.g. correct thermostat, efficient radiator

Remember: Most performance chips just basically advance the timing to achieve
a "feel" of more HP, i.e. generally little to no torque increases occur on 928s
as the EZK with knock sensors maxs the ignition maps.

Bottomline: Performance chips overall

Benefits - ??????????????
Costs - MANY

pappy92651

I just installed the stock chips. Fuel pressure is stock. We shall see if that does the trick. At least I will get an indication of change. I wasn't around for the 2003 smog check but seem to remember the tech mentioning the stock chips and how NOx suddenly dropped when they were installed. The part of the ignition timing curve that is most effected by the chips is in the test RPM range (or just off idle).

IcemanG17

Steve
Are you still running the air pump?