Emissions Help?

[Teb74]

Just asking for some emissions help. I've changed out a few parts and I'm still getting similar results each time, exact similar results for the hydrocarbon part of the test and the Nox... So far i've changed out the 02 sensor, Coolant Temp sensor, plugs, cap, rotor plug wires. So i'm thinking this could be a cat problem because the car has been running rich and made it go bad after so long? Overall the car seems to be running better after all those parts were replaced, yet i'm failing. Should i focus on other areas to get replaced like the EGR system or other parts, play with timing? Also the car is a '91 I used premium gas at the time. Oh well any help would be great before the next purchase on parts.

[yellow_jacket]

If you post the actual numbers that would be a big help. Without them I can't tell you much.

[Teb74]

Here's my readings as you can see the standard is the passing numbers and heres the posts of my three readings...

First test
THC g/mi standard: 1.20 readings 1.37
Nox g/mi standad 3.00 readings 6.00
Co g/mi standard 30.0 readings 20.5 (pass)

2nd Test (replaced plugs, rotor, cap, plug wires)
THC 1.63
Nox 4.95
Co 31.2 (now why did this fail and not before?)

3rd Test (Replaced O2 and coolant temp sensor)
THC 1.63
Nox 4.47
Co 19.8 (now this is the lowest reading of all the tests?)
oh yeah and then on this test they decide to pull the decibel meter and i'm 3 decibels away from legal... Crap

[idlafie]

CO emissions are often the byproduct of an overly rich fuel mixture

NO is produced when temperatures in the combustion chambers exceed 2500 degrees Fahrenheit. Excessive engine temperatures could be caused by a lean fuel mixture, by retarded timing, by carbon buildup inside the combustion chamber, by a malfunctioning engine cooling system, or a partially clogged catalytic converter which causes backpressure in the combustion chamber.

The function of the EGR System is to reduce NO. The EGR system does it by rerouting exhaust gases back through the intake manifold to lower engine temperatures.

To lower your CO & NO readings, you are going to have to check the timing & idle to see if they are set a 20 degrees, (timing) and 650 rpm (+/- 50 rpm). Follow the procedures set in the FSM...download a FSM from here...
http://www.ffdet.com/members/rich/Nissan/nissan.htm
http://www.zeroyon.com/TheSite/techservice.html

To make sure your EGR system is working properly, make sure the vacuum lines which run to the EGR valve & the secondary BPT valves are connected & functioning properly....vacuum lines often break/crack/melt due to age & excessive underhood temperatures.

Also try pouring some Seafoam, (http://www.seafoamsales.com/motorTuneUpTechGas.htm), into your crankcase, intake manifold & fuel tank so as to remove carbon buildup in the injectors, intake manifold, and combustion chamber. Carbon buildup in the intake & combustion chamber can lead to higher than normal NO readings.

And finally, if you can, drop your cat & inspect it. All those years of running rich could have caused the honeycomb inside your cat to melt & fuse together restricting your exhaust flow & causing your NO readings to rise.
I failed smog a few years ago due to a melted cat. Once I replaced the cat, the car passed smog with flying colors.

Anyhow, hope this helps.....apologies about the long post...
ID

[KLR142]

Anyhow, hope this helps.....apologies about the long post...
ID

Absolutely that helps! Thanks! Zak's car has how many miles on it now? 116k? But yeah, we were wondering about the EGR system. Hopefully that'll solve it, and if not we'll get a cat. But I guess we'll check to see if we have a melted cat first... PITA though probably... Right on, we'll see what we can do. Thanks man!

[Pacman]

Hmm, same problem. I fixed the codes and still running rich. I'm thinking fuel regulator. That a possibility?

[Teb74]

Hmm ended up buying a cat... going to install it, will let you all know the results hopefully that should do it. Overall so far the car feels like it runs better than it did can't report on my MPG yet.