NOX Problem

[Greaper_ca]

Newbie here,

My Celica keeps failing the etest. Both HC and O2 are well below the limit but my NOX keeps failing me. First read 955 over 757. second test was 1336 over 757 after driving it for some time. Don't know where to start on this.

[Qslim]

EGR systems are a good place to start when it comes to NOX-specific failures, take a look around and make sure the ports are unclogged and the valve operates like it should. It also helps everyone help you if you post the specifics of the vehicle you're working with, and just to clarify I'm assuming you meant CO instead of O2.

[Greaper_ca]

Thanks,

yes I meant CO. The Celica is a 2.2ltr. I just bought the car not even a week ago as is. The HC and CO were well under the limit for both the curb test and the ASM test.

Here were my results:

First test.

ASM

HC limit = 66 result = 15
CO% = 0.37 result = 0.18
NO ppm = 757 result = 995

Curb Test

HC limit = 200 result = 5
CO% = 1 result = 0.00


Second Test (done after a few days and running the car prior to the test)

ASM

HC limit = 66 result = 15
CO% = 0.37 result = 0.19
NO ppm = 757 result = 1336

Curb Test

HC limit = 200 result = 9
CO% = 1 result = 0.08

So there you have it. I don't think I need a new catalytic convertor. I'm hoping that the EGR only needs to be cleaned. I don't want to replace it since the part has to be bought from the dealer and isn't carried by CT or PartSource anymore. And it cost between $300 to $400.

[GTSTWINCAM]

1991 Celica GT-S 2.2l

15mph
HC Max 121 Avg 31 Meas 38
CO .76 avg .10 meas .44
NO Max 807 avg 237 meas 1834 FAIL

25mph
HC Max 96 avg 20 meas 32
CO Max .65 avg 0.09 meas .51
NO Max 746 avg 199 meas 1458 FAIL


EGR operates fine. Stall when vacuum applied to EGR.

Check Engine light code 71.

I will change the VSV located behind the engine block and below the intake manifold.

[GTSTWINCAM]

15mph
HC Max 121 Avg 31 Meas 38 PASS
CO .76 avg .10 meas .44 PASS
NO Max 807 avg 237 meas 1834 FAIL

25mph
HC Max 96 avg 20 meas 32 PASS
CO Max .65 avg 0.09 meas .51 PASS
NO Max 746 avg 199 meas 1458 FAIL

What I checked:

1. I applied Vacuum to the EGR and the car stalled. EGR works
2. I removed the VSV and applied 9 volts to it while blowing into the ports. The 9v applied makes the VSV click and blocks/allows air through. VSV works
3. I replaced all of the Vacuum hoses with new hoses.

Check Engine light is still on, triggering a code 71 (EGR).

I dont know what is left.

Im thinking the following..

BVSV (Bimetal VSV) located at the Coolant passage? Controlled by coolant temperature.



Lastly,
ECU

[spawnarc]

i had this problem with my 5th gen and it was the cat converter sadly. I just replaced it and it passed fine. I have the 5sfe engine and the cat is right off of the manifold so it wasnt that bad it was just finding a place to order it from.

[Doctor J]

Disconnect vacuum hose from EGR and plug in the vacuum gage instead. Secure the gage near the windshield so you can see it while driving. Go for a test drive at 15 mph, engine warmed up, the gage should indicate 10 plus inches of vacuum.If not check the EGR vacuum modulator (aka backpressure sensor) and make sure that the ports in throttle body are not plugged.
the 3 way cat converter failure usually will cause elevated HC and CO as well

[Greaper_ca]

I haven't gone to etest since I last posted. I did how ever found that the filter in the modulator was filthy so I cleaned it with air and I also found that one of the vacuum hoses connect to the modulator was melted away much like gasoline on rubber. So I replaced that. I was ready to do the etest then my exhaust pipe that carries the resonator broke apart. I've finally fixed it so this week it's getting etested. Let you know how it went.

[GTSTWINCAM]

I cleaned EGR, replaced Vacuum modulator.

Tested Vacuum @ EGR port while driving and I am getting vacuum.

I decarbonized the engine by spraying 50/50 ATF and water in the intake manifold while revving vehicle.

I will attempt a 4th smog

Wish me luck.

[Greaper_ca]

Ok it failed on me again. According to the techie, it's either the vacuum switching valve (VSV) or the dreaded Cat. There's nothing wrong with the EGR. He did a vacuum test on it. He's going to replace the VSV then do a decarbonization of the engine. If that fails then I'm looking at purchasing a Cat. Crap this is getting expensive. I could do this myself but the weather up here has been cold and terrible in the last month or so and I don't have an indoor facility to work on it so I have to resort to paying someone else to do it.

[Greaper_ca]

Woohoo, I got my pass.

[Doctor J]

Congratulations

[spawnarc]

okay I am feeling stupid because I posted before that I replaced the cat and that was my problem but I went this year for my test again and it is failing for the NOX again. I cleaned the egr and obviously I have a new cat so what could the problem be this is really aggravating?

[Greaper_ca]

Originally Posted by spawnarc

okay I am feeling stupid because I posted before that I replaced the cat and that was my problem but I went this year for my test again and it is failing for the NOX again. I cleaned the egr and obviously I have a new cat so what could the problem be this is really aggravating?

I had a problem with the VSV (Vacuum Switching Valve). The mechanic put one in and it passed. He mentioned to me that if this didn't work, the next step was to decarbonized the engine. And if that didn't work - replace the Cat. But in your case, it doesn't apply. You may also want to check your timing. This might be your problem. You may have to advance it a bit.