erubin2000

Thank you Paulo.
Yes the car (1990 LS400) does lots of short trips. Car has close to 200k miles. If the engine has some carbon in it can it be easily decarboned and is it reasonable to believe that could drop NOx by 300ppm? I know a faulty EGR can do that, but decarbon the engine? And what about a vacuum leak that can raise NOxs so high yet little O2 is measured in the tailpipe.

I changed the PCV grommet. That has got to be too simple a fix to dramaticly cut NOx. I was hoping the cracked PCV grommet allowed an excess of air into the intake above what the ecu can trim. If the ECU sufficiently compensates it wont run lean.

If I could read trim, assuming a 1990 LS400 (pre-OBDII) has a LT fuel trim, I could see if trim is maxed out trying to enrichen. BTW, the O2 sensors have not been changed and the MAF sensor has not been sprayed with contact cleaner.

But wont a lean running engine show high levels of O2 in the tailpipe, which my smog test showed as low, under 0.1%.

So maybe I should decarb? Good results with that?

I can't change the Cat, it's too much effort and high parts cost. The car is not worth it. I tried to convince myself that the CAT on these cars is not what dramatically reduces NOx anyway.

Should I clean out the EGR passage?

python

iTrader: (4)

dicer

Maybe just move from that crap state.

erubin2000

Crap state? Please. Tech help is most appreciated.

dicer

Most states after the car reaches a certain age they realize that most of the cars are so old they will not meet any sort of emission standards and that most of the required components to meet such standards are no longer available to purchase to then meet such standards. So after that time period of say 25 years the car then does not have to be tested anymore. Any state that requires testing after 25 years really has no thought process in their rule making. They can not force a car manufacture the keep making emission related parts for ever, especially for a hand full of cars that are still around and running. I have roots in that state and still stand by what I said. And Ca is one state that will not let you use after market catalytic converters, so when all dealers run out of them for the older cars then what? And if I remember you can not even use any after market exhaust component there? Just look at the online sellers like rock auto there is always a little note saying "not available in Ca". So did I cover the "tech" on this one?

erubin2000

By hook or crook I need to get through smog in CA. I dont have the luxury of moving out of the crap state of California.. Should I focus on decarbon the engine? It's a good candidate for carbon in the combustion port. Mostly short trips everyday (2-5 miles) and an occasional 15 mile trip once a week.

You refered to the catalytic converter. In the context of my post are you suggesting the problem with my car might be the CAT. My HC and CO are very low. I dont want to mix up my problem with state problems.

Fixmeister wrote: "The cats have little to do with NOx reduction here." Is this accurate?

dicer

Its hard to tell. I thought post #15 was very interesting on how a cat affects it.

Some study material
http://www.smogtips.com/failed-high-...rous-oxide.cfm

http://www.salemboysauto.com/faqs/faq-20.htm
Scroll down to Nox.

And after some study, a 1992 anyway has a 3 way catalytic converter, and they do reduce NOX. I do not have a manual for 1990 or 91, but since they all are gen 1 I'm sure its the same converter. So like the guy posted above, your cats maybe junk and be causing the problem, especially if you ruled out all the other obvious causes of the high Nox.

RA40

iTrader: (6)

The cats are working fine. No measures need be undertaken for them. Simply NOX is the result back at the EGR. The post about a cracked tube is what I've experienced as well. I don't know the application for signal voltage. Can you verify that the EGR tube is not cracked?

dicer

Read what I posted above #22, I'm using a Lexus 1992 shop manual. The cats that are 3 way have lots to do with NOX.

https://en.wikipedia.org/wiki/Catalytic_converter

erubin2000

Thank you Dicer,

One of the links you sent to me listed the following, my comments in red.

1. Improper operation of the EGR valve. Stuck open, obstructed, leaking, or misrouted EGR vacuum lines. My EGR is functioning fine.

2. Plugged EGR passages. Carbon build up in passages. The EGR is not completly plugged because my engine almost stalls when I activate it at idle. Should I go through the trouble of cleaning the passages anyway?

3. Over advanced timing. Doesnt ping, havent really looked at this.

4. Too lean of fuel mixture. Why would my O2 be so low if I had a vacuum leak. Is that an accurate statement to make? My O2 is under 0.1% doesnt that preclude a vacuum leak? If my EGR pipe was cracked/leaking wouldn't exhaust pressure push out rather than suck in air and possiblynhear an exhaust leak? A relatively small exhaust leak would not make me fail NOX. The positive pressure in the exhaust wants to push out, not pull air in

5. Engines cooling system in poor condition, causing excessive temperature. Does not appear to be the case. Will do a coolant service and replace with 50/50 mix of Toyota red coolant since I'm overdo anyway.

6. Malfunction of the electronic spark control (ESC), and knock sensor. Computer fails to retard timing. Engine not knocking/pinging.

7. Contaminated or bad catalytic converter. As you said it is a 3-way. Can the converter fail on the 3rd function (NOx) and still perform stellar with HC and CO?

This particular list did not include excess carbon in combustion port. Maybe I should decarbon.

Post #15 is interesting in that before CAT replacement the HC and to a lesser extent CO were quite high and NOX barely failed. In my case HC is very low and CO also. My NOX is real bad. I'd like to believe RA40 who says my CAT is fine. My NOx is so out of wack it made me initially think EGR as I've seen in other cars in the past that only fail NOx. I don't believe a 3 way cat is divided up into 3 discrete parts where 2 work great (HC and CO) and one fails miseranbly (NOx). Maybe that's how RA40 sees it (hopefully from experience).

dicer

Agree first check out the tube, I've never done it. I suppose trying to lower the rear of the engine?
Let us know what you find.

erubin2000

But a leaking tube would let exhaust out not air in. Am I missing something? I'd think the complaint would be exhaust leak, exhaust noise, not O2 into the EGR causing a lean hot burn w/high NOx. The EGR adds inert gas (exhaust gas) into the intake to lower combustion temps. If air was going there instead of exhaust I'd have an excess of O2. So we should rule out ambient air pushing through the positive pressure into the exhaust.

RA40

iTrader: (6)

Thanks for that link dicer. My take away is that the system is in a rich mode as paulo57509 mentioned in the prior post. One other sensor is part of rich air fuel ratios and the poor gas mileage would be a symptom as well.

(additional) The other components to this are in functioning order as erubin2000 states, then the cats are a possibility. I'd asked this when our cars had similar issues and the smog guy relayed that the cats wouldn't change the readings. The Toyota technician that resolved my issue found a piece within the EGR system that had failed. Cleaned and replaced those EGR parts, the NOX dropped while the other readings were relatively unchanged.

Frustrating issue and to be sure each step we'd be curious to take an reading to see what fixes prompted what results. That's costly unless one knowsa shop to run this type of experiment/testing.

dicer

This young fellow explains it very well. And you can see if that front reduction section is messed up you then have high nox. and whats left is something similar to the old 2 way converter, that is what I get anyway.

erubin2000

Thanks RA40,
I'll try cleaning the EGR and maybe look for what may fooling the engine control to think I'm rich. Try cleaning the MAF, replace O2 sensor...