Failed emissions, high HC and NOx.

[GTOger]

QUESTION IS UP-FRONT. Read the story if you'd like to weigh in!

Q: Dear readers, I'm wondering if I need new catalytic converters.

1990 ZR-1 with just over 38,000 miles.

Back in December, I took the car for the routine Texas emissions test, my 3rd since owning the car. For the first time ever, it failed. The HC and NOx were way out of whack.

Readings from 12/21/2012
HC High-speed standard: 148 ppm
HC High-speed tested: 209 ppm

HC Low-speed standard: 152 ppm
HC Low-speed tested: 229 ppm

NOx High-speed standard: 1047 ppm
NOx High-speed tested: 1915 ppm

NOx Low-speed standard: 1149 ppm
NOx Low-speed tested: 2064 ppm

I went back the next day after giving the car a thorough flogging, blowing it out on the highway, and making sure she was good and warm for the test. The result: hydrocarbons were worse, NOx was better, still failed.

HC High-speed standard: 148 ppm
HC High-speed tested: 212 ppm

HC Low-speed standard: 152 ppm
HC Low-speed tested: 244 ppm

NOx High-speed standard: 1047
NOx High-speed tested: 1503 ppm

NOx Low-speed standard: 1149
NOx Low-speed tested: 1793 ppm


The car sat for a couple weeks before we could make a trip to go see Corey at Henderson Performance Technology. Corey thought perhaps the car was running lean. As it turned out, it was a bit fuel-starved and needed a new fuel pump and strainer. Low fuel pressure = bad fuel atomization = bad burn and spitting unburned gas through the exhaust.

After the new fuel pump, the car felt a bit (not a ton) more responsive and wasn't smoking anymore (it had been collecting some black soot on the passenger-side bumper). Unfortunately, since Henderson Performance is not in an "attainment area" (which means they don't have to get emissions inspections there) we did not have a way to check for improvements. The recommendation was take it home, flog it a bit, get re-tested. If it failed, run some "Guaranteed To Pass" through it and try again.

So I did. Took it home, flogged, re-tested. FAIL.

Ran by to pick up a bottle of G2P (guaranteed to help you pass your emissions test or double your money back!). Followed all the instructions (added to a fresh tank of super unleaded, ran the entire tank, filled with fresh gas and re-tested). Went for another test. FAIL.

We're getting closer, but not close enough.

HC High-speed standard: 148 ppm
HC High-speed tested: 206 ppm

HC Low-speed standard: 152 ppm
HC Low-speed tested: 257 ppm

NOx High-speed standard: 1047 ppm
NOx High-speed tested: 892 ppm

NOx Low-speed standard: 1149 ppm
NOx Low-speed tested: 1420 ppm


Based on my poor memory of a discussion I had with Corey, as well as some other reading that I have done around the Interwebtubes, when we have high HC and high NOx that is a good indicator of a lean mixture or bad cats.

My working theory at this point is since we absolutely did have a fuel mixture problem, and we were likely spitting unburned gas into the exhaust, we've destroyed the cats.

But I'm just a dumb guy with a car. I'd love to hear either some confirmation or some other suggestions.

[XfireZ51]

Did Corey put a WB O2 on it? You should get a scantool and see what the BLMs are like.

[Marc Haibeck]

I suggest testing the efficiency of the catalysts. They should be able to reduce HC by x/4. For example if the HC going in is 100 ppm the HC going out should be 25 ppm.

The HC going into the catalysts should be about 100 ppm at idle. If it is higher I would suspect a misfire.

Use a scanner to look at the fuel trim at idle. It should be 128 +/- 5 for a healthy engine.

Are they using a sniffer probe in the exhaust pipe or collection cones? The cones collect all of the air from behind the car. If they are using cones a leaky gas cap can cause high HC. Use an exhaust gas probe to sniff around the gas tank. HC should be less than 10 ppm.

I believe that the number one cause for high NOx on LT5’s without EGR is carbon build up in the combustion chamber. You are heading in the right direction with the fuel system cleaner. I recommend CRC 05063 concentrated fuel detergent. Make at least 10 WOT runs to 90 mph while running the fuel detergent.

[GTOger]

Thanks guys! Xfire... ya lost me there, man! Just to re-iterate, I'm just a dumb guy with a car, so acronyms like WB 02 and BLM are beyond me. Sorry for being an idiot and posting in the technical section. :redface:

Marc, thanks for that. I'm not sure how to test for HC's on my own. Maybe there's a shop around that has a 5-gas sensor. Hmmmm.

The CRC 05063 is the exact stuff that I used. Everybody here apparently calls it "G2P" for Guaranteed to Pass. And I ran the car pretty hard. A couple of parts stores have also recommended Seafoam but my reading leads me to believe it's not exactly what I need.

Seeing as how my readings are SO far off the map, though, it just seems like this is beyond something that a bottle of additive will cure. Do you figure it's worth another bottle?

The testing stations here use a probe that sticks into the tailpipe. Once upon a time, in a hypothetical situation, it may be that a certain testing facility helped out by not fully inserting the probe and I got my sticker. But it was a long time ago that allegedly may have occurred to someone closely resembling me. Since then there has been quite the crackdown.

[Schrade]

The car sat for a couple weeks before we could make a trip to go see Corey at Henderson Performance Technology. Corey thought perhaps the car was running lean. As it turned out, it was a bit fuel-starved and needed a new fuel pump and strainer. Low fuel pressure = bad fuel atomization = bad burn and spitting unburned gas through the exhaust.

Yes - bad atomization (possibly from poor spray quality) would create a 'lean' burn (although the proper QUANTITY of fuel is going in), and some extra HC's are still gettin' by the cats.

This would burn hot, with increased NOx 's, and the excess HC's WOULD get catalized in the cats.

Might need only a squirt pattern check from Jon FIC Injectors.

Where's user hog? I think he's the chemist here - is he not?

[XfireZ51]

Thanks guys! Xfire... ya lost me there, man! Just to re-iterate, I'm just a dumb guy with a car, so acronyms like WB 02 and BLM are beyond me. Sorry for being an idiot and posting in the technical section. :redface:

There's no attempt here to make anyone feel foolish or stupid. Having said that, you can ask the questions to understand better. Corey is also very expert about this.
Basically, Marc and I have suggested using a scantool to better determine what's going on with the fuel trims in the calibration. The 128 is a BLM and means the fuel adjustment has reached equilibrium, neither lean nor rich.

"In a nutshell, the Block Learn Multiplier (BLM) is the long term fuel adjustment that the ECM "learns" to keep the air/fuel ratio within acceptable parameters. The Integrator is the same idea, only for short term adjustments. Basically, these two strategies are used to make adjustments and adaptations to the ever changing loads, atmospheric conditions, and fuel quality to keep the car's air/fuel ratio correct for driveability and emissions.
Also, keep in mind that when we say Long Term or Short Term, we are talking in computer time, not human time. In our ECM the Long Term fuel adjustment (BLM) happens about twice per second, while the Short Term fuel adjustment (INT) happens about 20 times per second."

[USAFPILOT]

did you try a can of denatured alcohol in the tank? Worked for me. However, I am running Headers and High flow cats with the stock tune. I had to pass in Houston.

Anyway...your car is about to be old enough to not have to pass the emissions, so don't sweat it too much.

[scottfab]

It'd be helpful to know what diag tools you do have. Not many of us have an exhaust sniffer but can you measure the temp of the cats? (Catalytic converters).
http://www.youtube.com/watch?v=TjPL4D9Mdck

One other baseline test is to bang on the bottom of the cats with your fist (when cold) and listen to any rattling there may be.
It's a sure sign of a bad cat.

Also there are many ways to ruin an O2 sensor. Maybe one or both are responding slowly (common failure mode if abused or old).

[Schrade]

did you try a can of denatured alcohol in the tank? Worked for me. However, I am running Headers and High flow cats with the stock tune. I had to pass in Houston.

Anyway...your car is about to be old enough to not have to pass the emissions, so don't sweat it too much.

I've suggested this too (ONLY as a short-term fix) in the past, but none that I've heard actually did it.

OP - are TX emission limits changed to more stringent limits, based on ethanol blended fuel?

If the BLM is far removed from 128 (+) or (-), it will show that the car has been running out-of-tune for quite some time. Exactly what ELSE it will tell, as far as diagnostic procedure, I'm in the dark...

[GTOger]

Xfire - thanks for the explanations! Looking back on my past posts here, this group has been nothing but helpful. I fell into my ZR-1 sort of by accident (another story, another day) but I'm glad I did. ZR-1 owners seem like they've got their acts together.

It'd be helpful to know what diag tools you do have. Not many of us have an exhaust sniffer but can you measure the temp of the cats? (Catalytic converters).
http://www.youtube.com/watch?v=TjPL4D9Mdck

One other baseline test is to bang on the bottom of the cats with your fist (when cold) and listen to any rattling there may be.
It's a sure sign of a bad cat.

Also there are many ways to ruin an O2 sensor. Maybe one or both are responding slowly (common failure mode if abused or old).

I've got an infrared temp sensor, and I've got not one but TWO fists I could use! ;) Now if I only had a lift.... <sigh>.

I haven't tried denatured alcohol. This is the first I've heard of trying that. Interesting.

Schrade, I don't know that the emissions regulations in Texas have changed due to ethanol. I'm not saying yes or no, I really have no clue.

USAFPilot makes a good point though. In 2 years, the car officially becomes "classic" and is no longer subject to the sniffer. Annual inspection becomes a safety-only proposition at that point. I'm sure as heck not going to park the car for 2 years, so the question becomes... would I get away with it!

Well I suppose the bottom line is (A) I don't want to be an environmental scofflaw and (B) the emissions system not functioning right indicates something upstream is out of whack. So I'd sort of like to get to the bottom of that mystery.

[GTOger]

It'd be helpful to know what diag tools you do have.

Oh, I have a couple of OBD-II cables and various pieces of software to use them. But I don't think that'll do me any good on this OBD-I car. What I ought to do is poke around and see what folks are recommending. I know the car will tell you exactly what's going on if you can ask it.

[Marc Haibeck]

A shop that advertises that they like to perform emissions oriented repairs will have an exhaust gas analyzer. Measuring the exhaust gas before the catalyst is not commonly done. They will need to weld a fitting on the pipe going into the catalyst.

For good emissions performance there is little tolerance for a misfire. The engine needs to be able to idle silky smooth. If not it should be investigated.

Note that a technician with a gas analyzer can probably give you good advice as to how the car will do on the next test based on the emissions readings, in the shop. This way you can verify that a repair is effective before going to the test.

[GTOger]

Thanks Marc . OK, I guess I better try a bit more diatnostic work. The engine seems to idle very smoothly to me. Then again, my daily drivers include a 3/4-ton GMC diesel and a 5-cyl twin-turbo Volvo. They're "smooth" in their own unique ways, which leaves the LT5 to really feel like butter! LOL.

I have a really good mechanic here locally. He's never worked on the ZR-1 - it's always gone to Corey. But that's a 5 hour trip and still no gas analyzer.

[curtsvette]

had the same problem the last 4 years . my 91 fails emissions bad . if i siphon out all the old gas and put in fresh gas it passes with flying colors. Its the ethenol in the gas. doing additives didnt help have to get all the bad gas out and new gas in to fix it. I just do that every year to pass. only 3 more years to have to fool with emissions in Texas luckily

[Z51JEFF]

My car failed a few times.I replaced both 02 sensors and put in 5 gallons of E85 and it finally passed.Not looking forward to the next test.In Ca they keep lowering the MAX levels allowable.My car with 6000 original miles wouldn't pass the current levels which are 502 MAX Nox,at 6000 miles the car had a Nox level of 702.Ca keeps lowering the MAX limits.