93 240 Failed emissions

[Dutch]

I failed my Colorado test in one area. The NOx. Maybe someone can help me identify what caused this.

HC - 0.0662 limit 2.5CO - 0.45 limit 20.0CO2 341.67NOx - 6.38 limit 6.00

I've recently have an idling and starting when warm problem but after replacing the hose between the EGR and the BPT which had a hole in it and removing the EGR and cleaning it which it was fine to begin with, I chose to test it.

It has very low HC and Co readings and barely slipped past the limit on NOx. Any advice would be great!

I have replaced the coolant temp sensor recently too

[InsanityInc]

what in the world rating system do they use for the emissions in colorado?

Like, are those numbers percents, PPM, or what?

However, low CO and low HC coupled with high NOx indicate a lean condition. Check for vacuum leaks.

[sleepyRPS13]

basically when your car goes slightly lean nox can pick up.

you look mostly at o2 and co for problems. hc can swing high at either direction.

nox -overheated engine-vacuum leaks-overadvance timing-defective egr

[Dutch]

I was amazed how low the other 2 readings were compared to what's allowed. And I just missed the NOx, I haven't checked the timing yet but will. I also will put new plugs in and pump in some 91 and go back. I think I have basic plugs but will put Bosch back in. Other posts I have seen indicate I have a bad/dirty AIV unit from starting and idling issues.

[NISTECH]

When posting emissions failure you need to include all 5 gas readings. You are missing your O2 reading. That is detrimental in diagnosing what you have going on. You also need to include the readings measure as insanity said. I suspect its all % readings. Here in california we use PPM for nox and HC and percentage for the rest. Your CO2 is not a percentage number so I suspect that is a PPM measurement. But with out an O2 reading I really cant assess what you have going on. I will say from what you did post it does NOT appear to be a lean condition or timing issue. If it was you HC readings would be elevated which they are not. A rough guess with out all the information is high compression or malfunctioning EGR or AIS system, more inclined to thing an AIS failure since you have done extensive EGR repairs. If the AIS is pumping O2 into the system when the car is warmed up [which it shouldnt] You will have an enourmous amount of O2 in the system not allowing the rhodium bed in the front half of the cat to break up the NOx. All the O2 would be worsening the situation by creating more NOx in the hot part of the manifold.

Dont take pop shots at the repair based on what I just posted. It was only to give you an idea of what MIGHT be going on. Get the rest of your information up for us to properly assess your problem. otherwise we are just taking shots in the dark.

[Dutch]

Looking at the printout... HC as all other tests are in GPM..? It's based on grams per mile... These 4 readings are the only ones listed on the printout.HC GPMCO GPMCO2 GPMNOx GPMand of course fuel cap pressure test.

I was reading a post from last fall of a guy with a 93 Altima who had similar readings and after finding 3 of the 4 intake passges plugged up he cleaned them out ansd passed.Do you know if the 93 240 has the same intake mani as the Altima? My issues are similar and if I have plugged passages in my intake I will remove and clean mine as well but didnt want to remove it if it's different.

[Dutch]

Also, My combustion pressure is actually lower than most, compression is at 155 PSI for all cylinders

[NISTECH]

Is it possible for you to scan your printout and post it. The standard smog machines either measure 4 gases or 5 gases the missing 5th gas is NOx on the 4 gas machine. You do have a 4 port manifold and should have 4 allen head plugs to gain access to the EGR passages above the cyl intakes. Yes this too could be your problem.

[NISTECH]

BTW I hate GPM measurments its the hardest to daig...lol

[Dutch]

I should be able to scan them and post the results. Do you happen to know if these allen plugs are on the bottom of the top of the mani? I dont have my car here at work to look. It would be nice if I could get to them and NOT have to remove the intake.

[Dutch]

I also have a color graph I can also add if needed

[Dutch]

here's the graph

[InsanityInc]

You're running lean.

Low HC, low CO and high NOx means you are running lean. The end.

[Dutch]

Two questions then... What's causing the lean mixture? Bad EGR system? What's the best way to richen it? Retard timing?

[InsanityInc]

Two questions then... What's causing the lean mixture? Bad EGR system? What's the best way to richen it? Retard timing?

No. Exhaust gas is inert (mostly)No. Your timing does not affect your fuel mixture

The two things to check for would be vacuum leaks and low fuel pressure.

[NISTECH]

He tested your car and stated you did not have AIS[air injection] when infact your car should have it. According to the diag traces you posted your HC was right in line for normal passing emission systems, not to low or to high.

[sleepyRPS13]

or cloggish injectors

[Dutch]

Since i put new injectors in about a year ago, stock from autozone, my guess is to check fuel line pressure. Is there a way to do this or would i have to take it to a shop? I just last week replaced the filter too. Any indicators to a fuel pump problem? Do those things loose pressure as they go bad or just stop working? My initial problems 2 weeks ago were hard starting when its warm out or if i drive it a few miles and then try to start it after letting it sit for a while. on a cold engine it cranked right up. Up till 2 weeks ago all was hunkydory

[Dutch]

Follow up to my last post. My #3 injector small O ring was shredded allowing fuel to drain into the cylinder. I replaced all injectors with NISSAN dealer units, new FPR, plugs-NGK, and passed this time. The plastic crown on #4 fell off as I pulled it out and it ended up past the intake and sitting ontop of the intake valve. Took an hour to fish the ***** out. Sure didn't want to pull the intake OR head for this little piece of $hit. The crown was deformed and was just about to comeoff on its own so i'm glad it didnt come off at 6K RPM.