jserio

When you have a high N.O. reading from smog, Can this only be cured with new cats?

perrys4

hey joe, I had a thread on this a month ago or so. my nox was high also but everything else was extremely low. Susan from Devek said they have had good luck with the lower temp thermostat. I ran this by Greg and he told me an interesting story. First off he didnt feel the thermostat would really have a great impact. Secondly he said they took a car to smog and it failed nox. They brought it back and put a new converter on it and it again failed. Brought it back and put a new fuel rail system in it and it again failed. He said they had several thousand dollars in brand new parts on it and it still failed. They got frustrated and took off all the new parts and returned it to as it was. Then Ken got the idea to try it at a different test center. It passed no problem. I guess the moral to the story was that the testing stations calibration can be off too and it may not always be the car. I know the stations are closely monitored but it makes sense to me. Two years ago the same shop that did my current smog was raving about how clean my car was for its age. This time it does as well but the nox are high. Not sure what to think but it is possible for the equipment to be at fault.

ROG100

Do a search for "Failed Emission test" to read my problems which I eventually solved.

Bernie

I wrote this up on my DIY site a couple of years ago......

Cheers


Hi All,
If you remember a little while ago I posted about my gross polluter status from the referee. I imported my shark to CA from Canada and had to do the gray market dance.
From some of the replies I received, I was concened that the repairs needed to get the car passed would be a little high.
I decided to do a check of my O2 sensor and it wasn't reading anything? So, I purchased a aftermarket Bosch sensor from 928Inter. and installed it. That's all I did.
Here are the numbers now.....

Original Test
At 15mph / RPM 1364
CO% = 0.01-----------limit 0.80
HC ppm = 117---------limit 128
NO ppm = 3287!!!!----limit 1127
________________________________________________
At 25mph / RPM 1809
CO% = 0.00-----------limit 0.60
HC ppm = 31----------limit 103
NO ppm = 2201!!!!----limit 987
_________________________________________________

Test this morning
At 15mph / RPM 1349
CO% = 0.02-----------limit 0.80
HC ppm = 28----------limit 128
NO ppm = 772--------limit 1127
________________________________________________
At 25mph / RPM 1348
CO% = 0.02-----------limit 0.60
HC ppm = 21----------limit 103
NO ppm = 773--------limit 987

IT PASSED!!!!
So now you know.....
If your car is suffering from high NOX, it does not necessarily mean that your cat is baked or your manifold needs work. I am sure that these things are definately contenders for creating high NOX but the O2 sensor was my culprit.
It made sense to me that if the O2 sensor was shot, the computer would have no information available at the exhaust to adjust.
The sensor was 60.00 and I put it in myself in 1 hour. Back to the referee next week to finish off my Canadian to USA conversion.
Cheers
Bernie

jserio

Thanks guys. I just hate buying parts that are not the problem. The N.O. limit was like 685 and my car was like 816. Not much off I think so I was wondering if you can tweek something to get it to drop that bit.

Ron, Thanks for sharing that incident. I am planning on going to a different station. The first one I used was a state facility.

dr bob

Joe--

Have the station run the car in test-only mode first, even if it costs some money. You only get a few consecutive failures before your car is tagged as a "gross polluter", condemning it to a life of test-only stations and much more careful scrutiny.

NOx is caused by high combustion temps. Might be lean (vacuum leak or weal oxy sensor), might be toasted cat (I know you have a spare), might be wrong plugs, etc. Timing on your S4 is not adjustable so that's not a likely issue for you. But you do have an overheating problem that definitely needs to be cured anyway, so maybe now's the time to get the radiator reworked or replaced and get those fans working right. BTW, Saab and Volvo cars use the same fan motors when you are prowling Ecology for used parts. You really just need bearings.

Anyway, my next test will have copper plugs, new wires/cap/rotor, no other changes. The only thing that changed from the first two tests were the plugs (to plus-4's) and the NOx results, from almost none to just barely failing. The tester took my suggestion to run the test in second gear and it squeeked by. I'll be back at it again in about a year.

Going up to Devek this weekend with the new car?

ViribusUnits

Two factors work on the NOx reading on 3 way cat equiped cars. Peak combustion chamber tempreture, and O2 concentraion in the exauste.

For the NOx reduction part of the cat, there needed to be minimal, almost no, O2 in the exauste gas. The catylist is very sensitive to the O2 in the exauste. For your S4, that's basicly unadjustable. If the O2 sensor, or MAF are off, it could cause this problem.

The easyest way to kick the combustion chamber temps down is to retard the ignition timeing. On your S4, IIRC, the timeing is computer controled. That means it's pretty much unadjustable outside of aftermarket chips, BUT the idea of GIGO still applys. If eighter the Temp II sensor, or the Temp I sensor are reading cold, the computer will mistakenly advance the timeing. Course it's always possible, if unlikely for the computer to be off.

Good luck.

jserio

Dr. Bob, Since you jiggled the fan wire the temp has not even touched the third white line and that included the bumper to bumper traffic. We both heard the bearings so it will be an eventual problem but it can hold for the moment. I wanted to post this thread to see if putting on those used cats was avoidable. I recommended Fast German before so I will let him have the car for a few days and if he doesn't kill me on the smog repair I may be able to have a few other things address. I won't be able to make Devek Days as immediate cash outlay will definitely strap me to the post. But we'll catch up at Sharktober Fest and maybe even big red will be able to make a presence.

dr bob

Joe--

The fans should not even be on at freeway speeds. Your brother was driving with the heater on even at superlegal speeds, and had heating issues. That means radiator. The fan bearings are toasted becuase the controller tells them to run all the time... because the radiator isn't quite doing its job. So, you have two symptoms of radiator problems: heating even at freeway speeds, and fan bearings worn out. Cure the problem first, then fix the collateral damage to the bearings.

Maybe after that we can get your AC back online too. Wouldn't that be cool!

Styln928

I wish I was still in SoCal & acessable to DrBob's knowledge. I want cold A/C too! I told myself i'm not buying another car without working air. Wow, was I wrong. My biggest mistake was not driving Joe's S4 straight to Dallas and telling him it's a POS and i'm saving him from a hugh headache. But I beat him out of Ole' Blue so I guess I owed him one. The problem is . . I've been paying dearly ever since.