Failed Emissions, specifically NOx

[CDG]

I have recently had my car Smogged and it failed NOx emissions, the other readings are average to better than average, my mechanic says Cats, but the ECU says replace the O2 sensors, which he did and retested using his older smog tester(which does not test NOx) and he says its not changing much.

I said we need to give the ECU time to recalibrate, he says he still thinks I need Cats.

Car has never had the O2 sensors changed, and has 185k miles.
I had also put in 1 litre of MethylHydrate about 100 miles ago(before new O2 sensors were replaced), and retested with almost no change in the NOx reading.

I was wondering if anyone has an opinion of whether or not the SVX's need Cats that often.

[Subafreak]

9 times out of 10 it need cats. Or if the readings are not that far off it might just be the EGR valve, you might want to have him make sure it's working. If so it might be time for a custom exaust.


My SVX passed emissions with no cats.

[gl1674]

Chris,

As far as I remember leaner mixtures reduces CO but increases NO emissions. Richer mixtures increases CO but reduces NO. Something to do with a temperature in combustion chamber.
The lower the temp the better.

From the practical consequences - EGR valve is a suspect, EGR does lower the combustion speed/temp. But it should have set a code in ECU if it is faulty...

Cats don't like to be mistrated with incorrect mixture - too rich may cause them to overheat and melt. Bad O2 sensors may cause that. Depending on how many attempts you can have with the emission testing I'd think about replacement cats... Anybody has any experience with used cats?

Try that "Guaranteed to pass" fuel additive (very powerful fuel system and cat and o2 cleaner). I've seen it work on my fathers 93 Ford Crown Vic, and it was well worth the $10.

[TomsSVX]

guarenteed to pass is good ****, my buddy used it in his 93 k1500 which had 185k on a chevy 350!! this engine and exhaust were beat as hell and it passed w/ flying colors. Try it out it's guarenteed and it's wicked cheap

[CDG]

I just might have to try the Garranteed to Pass stuff.
I replaced the O2 sensors, and ran it thru the emissions test again, Now NOx and HC Fail.
What a PITA.
btw, CAN$800 x 2 for front Cats. No thx.

Perhaps another litre of MethylHydrate in the tank, and a drive to Arlington Annual Awards Dinner may help

[CDG]

Just an FYI, after replacing my 2 O2 sensors the SVX is getting better fuel economy.
250 miles plus per tank compared to 200 before new O2's

[jsvxstyle]

give me a call let me know the readings. i direct you to the source, with a few test you can do to kill nox off.

[CDG]

I ran my car through our AirCare again after the new O2 sensors and running the car for about 4 days. Now my reading are as follows:
HC: Max allowed=0.5000 my reading=0.5538 FAIL,
normal average is 0.2571
CO: Max allowed=9.3200 my reading=1.1375 Pass,
normal average is 1.4348
NOx: Max allowed=1.2400 my reading=1.4620 FAIL,
normal average is 1.1073
all tests are measured in g/km

My mechanic thinks I need new front Cats, but they are $800 each, if I spend $600 on emissions repairs I get a conditional pass, good for one year instead of the normal 2 years, then I do it all again.
I really want to fix the problem, but don't want to waste $1600 on Cats I don't need. If they are truly the problem, then I'm ok with it.

Also, car is running much better, quicker response, and a little zippier.

[CDG]

OK, I just spoke to mechanic after talking with jsvxstyle.
As per J, I checked on the universal O2 sensors he installed and he said sortof:
He initially installed the NGK universal 3 wire O2 sensors. then ran the onboard sensor diags on the Suby, as you mentioned, and they failed. so he took out the NGKs and looked for the factory ones, nothing around(now there's a surprise) so looked for other, what he actually ended up installing were 2 Bosch Universal 3 wire O2 sensors, ran the sensor diag, and it came out clean.
So, I'm not sure if I should really worry too much about the sensors now and focus on my real issue.
Which as you mentioned:
1.Check the EGR valve.(left out detailed description)
2.Check PCV.(left out detailed description)
3.Check those intake bolts?? I know where it is.(left out detailed description)
4.then measure differential temps before and after Cats. to confirm if my Cats are toast.

Or, imagine my mechanic is good at WAGs and try some Cats just to see how lucky he is.
I am allowed to buy time to fix this problem, so I have another 3 months to try some other things.

Thanks to jsvxstyle for the 1.5 hrs of your time last night. You obviously know your ****, and I want to thank you for your help so far, and let you know that I will be talking to you shortly. After I look at 1,2 and 3.

[jsvxstyle]

let me know on all three test.. if there good. than you have two more to confirm, and the last two are pretty easy.
no problem on helping you out. let me know wuz up on the testings

[gl1674]

Chris,

Did you get O2 readings as well? If you do not see 0.5 - 1.0% O2 in the exhaust you should question your O2 sensors if they make the engine run too rich.

I dug out my last years test data with 154k. Surprise surpise they did not measure NO and this is California.
Here is what I had at idle - just in case:
HC (ppm) Max 120 Average 29 My car 15
CO(%) Max 1.0 Average 0.1 My car 0.01
O2(%) My car 1.0%

At the $$$ you quoted for the new converters I'd use all other options including borrowing somebody elses converters to make 101% sure they need replacement (you are welcome to borrow mines if you can make it so far south - hey it's only couple of hours flying time :-)

By the way, 1% CO is achievable on a carburateur car without any catalytic converters... Not surehow % it translates into your units.

[CDG]

Thanks for the feedback gl, our tests are done on a dyno, there is no idle test for all-wheel drive cars anymore. And I'm not sure how they measure O2, nor does my report show this.

But you and JSVX are right, I'll try all other options before I commit to Cats, JSVX has also offered to lend me some Cats to pass, but If they are truely bad, I'll put in new ones. Most likely some rebuild Cali ones that JSVX says are available at a much more reasonable price than $1600CAN.

Another clarification, I have revisitted the actual fuel economy I thought I was getting, and its actually no better at all, my new O2 sensors appeared to be improving both performance and fuel economy, but in fact the performance is a little better, but the economy may be a little worse. My tests were under differentr conditions. Auto vs Econ. We have had a rather dry spell resently, so I have been using Econ instead of Auto.

[CDG]

As it turns out, my emissions problem was a simple hose at the bottom of the air box going into the intake manifold. The hose was off, and kept falling off every time I put it back on.
I have it on, and tested it, passed.

[oab_au]

Originally posted by CDG
As it turns out, my emissions problem was a simple hose at the bottom of the air box going into the intake manifold. The hose was off, and kept falling off every time I put it back on.
I have it on, and tested it, passed.

Hi Chris. It is great to have these problems, turn out to be the cheap simple things.

Harvey.