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View Full Version : At the end of my NOX rope, so I cheated.



TbirdSCFan
03-21-2011, 05:10 PM
I've never had to admit defeat on a Nox emission problem, but this time it just plain wore me down. My red car has always seems to have more torque and pep than the other 2. I didn't give it a lot of thought, but when the mileage was not so great, and I flunked a smog test, I figured out that the EEC was enriching the mixture and that had fouled the cats after a year or so.

So, having 3 SCs has its advantages.. I simply swapped EECs, and watched the temps and it worked great.. mileage back up in the 20s. Then later, swapping over the exhaust/cats from 5spd to auto, fixed my Nox problem. At least for a while. I also routinely clean the cylinders with seafoam to reduce the carbon buildup and hence the Nox.

Well this year, nothing I did worked. After cleaning the engine and swapping out to a different set of cats, swapping out ECT, ACT, MAF, BAP sensors, testing every vacuum line for leaks, resealing IC tubes, and even pulling the octance plug, it STILL failed. :confused: Swapped out the EEC again in a head scratching attemp and still no pass. No codes were set and a cylinder balance test was clean.

I did not install new O2s because the HC, CO, CO2 levels were all good and Nox is not generally affected by O2 readings. However, I believe that a degraded (i.e. old) O2 can cause a running condition which MAY cause the cats to degrade as time goes on. So after 5 retests, I finally threw in the towel and pulled the SPOUT plug to fix the timing at 10 degrees and it passed easily. I am convinced that it is running too lean AND that there's too much timing advance, but I cannot figure out what the heck is causing it. Car runs great, just high Nox :confused:

S_Mazza
03-21-2011, 05:47 PM
I did not install new O2s because the HC, CO, CO2 levels were all good and Nox is not generally affected by O2 readings. However, I believe that a degraded (i.e. old) O2 can cause a running condition which MAY cause the cats to degrade as time goes on. So after 5 retests, I finally threw in the towel and pulled the SPOUT plug to fix the timing at 10 degrees and it passed easily. I am convinced that it is running too lean AND that there's too much timing advance, but I cannot figure out what the heck is causing it. Car runs great, just high Nox :confused:

Leaky intake gaskets?

Harmonic balancer slipped, messed up your timing?

XR7 Dave
03-21-2011, 06:12 PM
Does your state do idle only testing or was this on the rollers?

slowpoke
03-21-2011, 06:20 PM
i have a question here, this year our wonderful government approved an increase of methanol in our fuel up to 25% mixture. that being the case could that cause this guys problems?

btw, im not saying that his fuel provider is doing the 25% mix but it has been approved to do and i know they are doing it alot in the mid-west atm.

txsc
03-21-2011, 11:22 PM
So now you know how to get it to pass smog; pull the SPOUT. After you clear that annual hurdle, put it back and enjoy the other 364 days.

JD

TbirdSCFan
03-23-2011, 12:21 AM
Does your state do idle only testing or was this on the rollers? Its a load test. It would pass the high speed test 25mph, but not the low speed 15mph.

Having read up on the Nox problem and how cats do their thing, most everything I saw said that cats are not usually the problem with high Nox if HC and CO2, etc are within specs. Taking that with what I know from experience, usually carbon build up (older dirtier engines) is what elevates the combustion temps to the point of producing Nox. So if you can clean the cylinders, Nox will usually drop, as I've seen. This is what the RXP stuff accomplishes. I ran seafoam through on 3 different occasions with a good amount of smoke (carbon burn off) 2 times.

I suppose the engine COULD be building up carbon in just a few days, but the thing runs great.. no oil smoke, no fouled plugs, no hard starts so I don't think its rings. I do have an occasional stumble at idle that is perplexing... like the spark just cuts out and then everything goes back to normal. Swapping EECs, DISs, and every other sensor I can get my hands on hasn't cured it. I've tried cleaning ground straps and connectors. Also... no codes are being set. My next part-throwing-guess will be the crank sensor to see if I can clear that up. :confused: Maybe its an intermittent problem? :confused:
But still, even with a misfire, HC,CO,CO2 are all at acceptable levels.

Im leaning towards the theory that maybe the cats have degraded but not failed outright and that the engine is running lean (or timing is advanced) and producing more Nox than they can process. So my shortcut gets me going for another year, but didn't solve my mystery...

Only other thing I can think of is that I use RTV sealant on the IC tubes that isn't labelled as sensor safe. But the amount is so small that I cannot possibly believe that its fumes or strings are enough to cause an O2 or Cat problem. But on the other hand, the Nox levels have been increasing over the years so who knows.

TbirdSCFan
03-23-2011, 12:38 AM
So now you know how to get it to pass smog; pull the SPOUT. After you clear that annual hurdle, put it back and enjoy the other 364 days.

JD :D Precisely what I'm doing this year.. I put in quite an effort to get it legal, but after the 6th test, I threw in the towel and went what I knew would get it passed. :D

XR7 Dave
03-23-2011, 07:57 AM
Never throw parts at a problem, shame on you. :p Have the engine smoke tested. Sounds a lot like a vacuum leak. Also, have you cleaned your MAF lately?

Mike8675309
03-23-2011, 09:39 AM
high nox values are usually due to excessive cylinder temperatures. This is most often due to overly lean conditions. Any chance you have a check engine light but you have it unplugged? I'd pull codes.

This would most often be caught by the o2 sensors when closed loop and the EEC-IV would try to trim it out. If it couldn't correct enough it should throw a code.

Vac leaks could certainly be a cause. a dirty maf incorrectly reading air mass could also be a cause. If you were running rich, HC's would be high.

TbirdSCFan
03-23-2011, 11:29 AM
Never throw parts at a problem, shame on you. :p I do feel shamed.. :o But when you have a couple of spare SCs, its just too easy. :D


Have the engine smoke tested. Sounds a lot like a vacuum leak. Also, have you cleaned your MAF lately? I'm with you on that, pulled every vac line out and inspected with the old on test.. :eek: replaced any that were questionable, even plugged a couple just to eliminate them. Swapped and cleaned the MAF.

When I ran the seafoam through the bulk of the smoke came out the tailpipe as expected, but I was getting a small amount in the engine compartment near the driver side exhaust manifold. Now I suppose that if smoke could get out, then air could get in possibly before the sensor?? :confused: But it was a very small amount, and no noise.

ThunderRoad
03-23-2011, 11:42 AM
NEXT YEAR SAME THING SO I GOT CLASSIC TAGS OR KEEP UNDER 5000 MILES A YEAR:eek:

dbd
03-23-2011, 10:24 PM
Had the same problem in California last year_Part of our problem is they make the requirements harder to meet each time.
Posted a before and after the new cats. CARB will only allow certain cats as a replacement. They are trying to get the older cars to run as clean as a brand new one. Look closely at the NOX measured before and after the cat change.

Later
dbd

WOW
04-06-2011, 10:53 PM
Ok, am I missing something here? Isn't EGR used to reduce NOX at idle and low throttle. Maybe your EGR valve is bad or sticky?