Bad Cats ??

[Yellow Rose]

First off, a request please, to maintain the technical aspect of this thread. We don’t need to go through the legal / moral / environmental debate of running without the cats - that has recently been done in another thread. Thanks, okay, here goes.

I took the cats off last year and placed them in my garage. Although the garage has a small AC for the summer months, by no means is it “climate controlled” with regards to humidity. This may or may not be a factor as you read on. Over the weekend I put the cats back on, in preparation for the annual inspection. Besides a little dust, one of the cats had roach droppings in it. Lovely. I managed to get all but a few pieces out. I left the remaining few pieces as is, for fear that I might damage the catalyst by picking out the debris. Besides, I figured that it would eventually burn out.

Important side note - my car has never thrown an ECU code. I’ll come back to this issue shortly.

In Texas there are two emission test speeds - 15 MPH and 25 MPH. My car failed the low speed miserably, despite having passed it last year with the same fuel / timing maps for steady-state driving, in other words, not under boost. I drove the car for only fifteen or so miles before going to the inspection station. Approximately half of the miles were at highway speeds. Below are the limits / readings for my test results.

High Speed

HC - 120 PPM / 120 PPM
CO - 0.67% / 0.17%
NOX - 848 PPM / 173 PPM

Low Speed

HC - 124 PPM / 501 PPM
CO - 0.69% / 0.86%
NOX - 937 PPM / 1293 PPM

Last year, the numbers were:

High Speed

HC - 120 PPM / 66 PPM
CO - 0.67% / 0.10%
NOX - 848 PPM / 302 PPM

Low Speed

HC - 124 PPM / 123 PPM
CO - 0.69% / 0.33%
NOX - 937 PPM / 546 PPM

Before the inspection, I loaded a different fuel map into the SS box. This map leans fuel under boost, but contains the same cell values for steady-state driving as was in the car for last year’s inspection. Before loading the map, I cleared the ECU by pulling the clock fuse. In retrospect, perhaps I should not have done this, because the LTFT and STFT just got erased.

The EGR valve’s purpose is to recycle some exhaust gas back into the intake, resulting in lower NOX. If my EGR valve was not opening properly, the lift sensor would’ve sent a code to the ECU. As I mentioned above, the CEL has never come on, so as to indicate a problem somewhere.

Right now, I have 87 octane in the tank. I think I read somewhere herein, that burning lower octane fuel results in less NOX. Is this true? On the other hand, a fellow gearhead said that for his inspections, he fills up with 104 octane because it burns cleaner. Is this true?

Could it be that the ECU simply needs some time to re-learn the fuel trims and that the cats need more time to be “cycled” so they are working again? Or, could I have permanently damaged the cats by leaving them on the shelf for a year?

 

[Briank]

Right off I would say your "cats" are fine, my first guess is that you have a o2 sensor that is failing. Your HC is high so I would not worrie about the NOX #. There is a test procedure in the manual for the O2's that you could do to and see if you can get a code. It just involves running the engine at a set rpm for a certain length on time.

Page 212 of the online manual

 

[Yellow Rose]

Right off I would say your "cats" are fine, my first guess is that you have a o2 sensor that is failing.

Respectfully, I'm not sure that I would totally agree. My understanding is that an O2 sensor is either working or not working, with no in-between. Even if it does operate on only an intermittent basis, each time the O2 sensor goes into the "fail" mode, it would send a code to the ECU. The ECU would then illuminate the "Check Engine Light" on the dash. My CEL has not come on in approximately ten months, so this should rule out a failed or failing O2 sensor.

Your HC is high so I would not worry about the NOX #.

Why do you say to not worry about NOX? It is too high for a reason.....a reason that is preventing a passed inspection.

 

[Briank]

Andy

Looking over your test results for this year I noticed that your HC readings were on the limit for the high speed test and way over the limit for the low speed. I am not sure how you pass or fail if the low or high is used but either way the other is used to help diag the problem. Your low speed HC readings were about 4X spec where as your other readings were just over spec. I would think it would make sense to work on the worst item first.
JMO

Brian

 

[BryanZublin]

Andy,
I think Kendall had a similar problem as you and could not pass the CA smog test unless he changed back to stock injectors and removed the Split Second box. Do a search - he posted on it extensively.

There should be a procedure in the manual for testing if the EGR valve is working correctly. Just because the ECU has not illuminated the CEL does not necessarily mean that the EGR is operating correctly. It could be that the MAP voltages coming from the SS box indicates to the ECU that it is not in the proper range to operate the EGR. Just a theory.....

Another possibility is clogged EGR ports (on the exhaust side), but we would probably have heard of this from other owners as the NSX ages.

Good luck.

 

[canuck]

If I may wade in on this, here goes:

An O2 sensor can"fail" and not throw a code. The O2 sensor generates a voltage between .1 and 1.0 volts. It also must switch back and forth over the magic 0.5 volt mark a certain number of times per 10 seconds. A "lazy" sensor will not throw a code on older models as it always generates a voltage between .1 and 1.0, but may only be cycling once per 10 seconds instead of 7 or 8 times per 10 seconds.

An o2 sensor will not cause a NOx failure. A failure in this is due to excessively high combustion temps. So low octane fuel ignites quicker, car runs leaner, leaner means higher combustion temps.

To fail on all 3 measured areas leans toward cats not at their required operating temps, or cats that are tired.
They should not have failed from just sitting in the garage. Your #'s from last year were marginally passable. Is your thermostat staying open and keeping the car in open loop at kow speed?
If it is okay, then I feel the cats are just tired and not efficient anymore.

To be sure you would need to do a couple of tests. Measure the temp of the exhaust before and after the cats with a optical thermometer. Secondly, measure exhaust gasses before and after the cats. A good emissions repair shop should be able to help.


Hth.

 

[nsxtasy]

Bad Cats ??

If I might offer a bit of humor, click on this banner:



Hope you find the problem, Andy.

 

[kpond]

canuck,

You offer some very sound advice, but you must know that Andy's car is far from stock and there's likely some other "issues" here. Although I cannot explain how Andy managed to pass last year, my thoery is that the SS box which is programed to pass lies, lies, and more lies to the ECU of MAP values, has caused the ECU to set the EGR valve position incorrectly.

As BZ correctly states, I too had this problem and was only able to resolve by re-installing my stock injectors and bypassing the SS box. I passed on the first try after these mods. Not too bad of a chore every other year (California).

 

[canuck]

canuck,

You offer some very sound advice, but you must know that Andy's car is far from stock and there's likely some other "issues" here. Although I cannot explain how Andy managed to pass last year, my thoery is that the SS box which is programed to pass lies, lies, and more lies to the ECU of MAP values, has caused the ECU to set the EGR valve position incorrectly.

As BZ correctly states, I too had this problem and was only able to resolve by re-installing my stock injectors and bypassing the SS box. I passed on the first try after these mods. Not too bad of a chore every other year (California).

Sorry, newbie here, was unaware of his heavy mods.

 

[Yellow Rose]

A failure in this is due to excessively high combustion temps. So low octane fuel ignites quicker, car runs leaner, leaner means higher combustion temps.

So 104 (vs 87 in the tank, right now) octane gas should help, right?

To fail on all 3 measured areas leans toward cats not at their required operating temps, or cats that are tired.

Agree, but.....

They should not have failed from just sitting in the garage.

I can see that when cats begin to age, the emission numbers will gradually begin to rise. But to jump by a factor of 2x to 4x is not within the normal catalyst degradation.

Measure the temp of the exhaust before and after the cats with a optical thermometer.

What temperature should we be looking for? By the way, the car is supercharged with 8 PSI at redline. However, the fact that it has forced induction, per se, is irrelevant because the emission test is such that the engine intake is under vacuum.

 

[sjs]

I too would at least consider the cats, as well as a lazy or inaccurate O2 sensor. Both suffer in a car that runs too rich. I’m not sure how standard O2 sensors act when subjected to unburned fuel, but widebands continue to work as the readings drift towards falsely lean. Perhaps your sensor appears to work but is centered on the wrong AF. Does anyone know definitively if standard sensors “fail” in this way? That should be simple enough to check with a voltmeter and your FJO.

I believe that cats also die young when the AF is too rich. Since you previously ran the CTSC which is almost always a bit fat in the midrange for safety, they may be “older” than mere miles suggest. Most early BBSC cars also seemed to run very rich in the middle of the power band, but perhaps you had already removed the cats by then. If they have been out since the last time you passed then perhaps they are not the primary problem but could still be weak.

 

[Yellow Rose]

Good Cats

Well, as it turns out, the cats (and O2 sensors) are fine. After driving around for a couple of weeks, perhaps all that was needed was to burn off surface oxidation that accumulated on the catalyst over the past year that the converters were just gathering dust (and roach droppings) in the garage. The moral of the story is to have the cats on the car for a week or two, prior to getting the emissions inspection. Having pure 104 octane in the tank doesn’t hurt, either. Obviously, the higher octane improves (lowers) some of the readings. But at five bucks a gallon.........

This year, the initial numbers (failed) were:

High Speed

HC - 120 PPM / 120 PPM
CO - 0.67% / 0.17%
NOX - 848 PPM / 173 PPM

Low Speed

HC - 124 PPM / 501 PPM
CO - 0.69% / 0.86%
NOX - 937 PPM / 1293 PPM

Last year, the numbers (passed) were:

High Speed

HC - 120 PPM / 66 PPM
CO - 0.67% / 0.10%
NOX - 848 PPM / 302 PPM

Low Speed

HC - 124 PPM / 123 PPM
CO - 0.69% / 0.33%
NOX - 937 PPM / 546 PPM

This year, the re-tested numbers (passed) were:

High Speed

HC - 120 PPM / 58 PPM
CO - 0.67% / 0.17%
NOX - 848 PPM / 173 PPM

Low Speed

HC - 124 PPM / 122 PPM
CO - 0.69% / 0.17%
NOX - 937 PPM / 260 PPM

Regardless, there is still something amiss with the low speed HC value. Could there be too much timing (not enough retard) for the 15 MPH test while the engine is under vacuum?