Passed Smog, but very high NOX?

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Apr 15, 2010 | 04:09 PM

CrazyDude

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Full Member

Joined: Jan 2002

Posts: 172

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From: Pasadena, CA

Passed Smog, but very high NOX?

Hey folks. I finally got my car to pass smog here in CA! All that fretting about my air injection, and it turned out to get just a corroded connection going to one of the two solenoid on the ACV.

Anyhow, my smog results are below. I was having a problem with VERY high NOx. With normal timing set, I was getting ~700 ppm. To get it to this level, the timing is retarded as far as it can go: CAS is all the way counter-clockwise.

All my other numbers look fairly good, right? Here's my current hardware:
- 1991 NA, 40K on a rebuilt engine
- Turbo S5 rotor housings
- Turbo S5 intermediate plate
- Slight intake manifold porting
- K&N drop-in air filter replacement
- Stock exhaust manifold
- New Magnaflow converter, 2.25" inlet/outlet, with air injection
- RB presilencer
- RB Catback
- All emissions equipment in place
- No engine fault codes

<html>
<table style="text-align: left; width: 800px;" border="1" cellpadding="2" cellspacing="2">
<tbody>
<tr>
<td style="vertical-align: top; text-align: center;"> 
</td>
<td style="vertical-align: top; text-align: center;"> 
</td>
<td style="vertical-align: top; text-align: center;">% CO2 
</td>
<td style="vertical-align: top; text-align: center;">% O2 
</td>
<td colspan="3" rowspan="1" style="vertical-align: top; text-align: center;">HC (PPM) 
</td>
<td colspan="3" rowspan="1" style="vertical-align: top; text-align: center;">CO (%) 
</td>
<td colspan="3" rowspan="1" style="vertical-align: top; text-align: center;">NO (PPM) 
</td>
<td style="vertical-align: top; text-align: center;"> 
</td>
</tr>
<tr>
<td style="vertical-align: top; font-weight: bold; text-align: center;">Test 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">RPM 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">MEAS 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">MEAS 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">MAX 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">AVE 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">MEAS 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">MAX 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">AVE 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">MEAS 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">MAX 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">AVE 
</td>
<td style="vertical-align: top; font-weight: bold; text-align: center;">MEAS 
</td>
<td style="vertical-align: top; text-align: center;">Results 
</td>
</tr>
<tr>
<td style="vertical-align: top; text-align: center;">15 mph 
</td>
<td style="vertical-align: top; text-align: center;">1844 
</td>
<td style="vertical-align: top; text-align: center;">14.8 
</td>
<td style="vertical-align: top; text-align: center;">0.5 
</td>
<td style="vertical-align: top; text-align: center;">81 
</td>
<td style="vertical-align: top; text-align: center;">37 
</td>
<td style="vertical-align: top; text-align: center;">21 
</td>
<td style="vertical-align: top; text-align: center;">0.52 
</td>
<td style="vertical-align: top; text-align: center;">0.10 
</td>
<td style="vertical-align: top; text-align: center;">0.02 
</td>
<td style="vertical-align: top; text-align: center;">554 
</td>
<td style="vertical-align: top; text-align: center;">218 
</td>
<td style="vertical-align: top; text-align: center;">466 
</td>
<td style="vertical-align: top; text-align: center;">PASS 
</td>
</tr>
<tr>
<td style="vertical-align: top; text-align: center;">25 mph 
</td>
<td style="vertical-align: top; text-align: center;">2054 
</td>
<td style="vertical-align: top; text-align: center;">14.8 
</td>
<td style="vertical-align: top; text-align: center;">0.5 
</td>
<td style="vertical-align: top; text-align: center;">63 
</td>
<td style="vertical-align: top; text-align: center;">29 
</td>
<td style="vertical-align: top; text-align: center;">15 
</td>
<td style="vertical-align: top; text-align: center;">0.43 
</td>
<td style="vertical-align: top; text-align: center;">0.08 
</td>
<td style="vertical-align: top; text-align: center;">0.01 
</td>
<td style="vertical-align: top; text-align: center;">511 
</td>
<td style="vertical-align: top; text-align: center;">204 
</td>
<td style="vertical-align: top; text-align: center;">475 
</td>
<td style="vertical-align: top; text-align: center;">PASS 
</td>
</tr>
</tbody>
</table>
 </html>

The ONE problem on my car was a high idle. Even when warm, the car idles at around 1000-1100 RPM. I haven't been able to figure out where the problem is yet; I've sprayed starter fluid everywhere and not found a leak yet.
Because this is an S5, there's not many ways to adjust the idle speed : No trim resistor by the shock tower, no adjustment screw on the BAC valve. I'm pretty sure that it used to idle at 750-850 properly after I rebuilt it.... don't remember when/where it started doing this.

I've thought through it a bit, and here's some possibilities that I've come up with:
- The catalytic converter is getting to hot : I put the convert in myself, and it comes right after the stock exhaust manifold, so I can also fit the RB presilencer + catback. As I understand it, NOx catalyzation rate goes way down when the converter gets too hot.
- Bad vacuum plumbing : I've started to replace some vacuum lines with silicone, as the originals were starting to fail. It is possible I plumbed up something incorrectly... damn, that's going to be hard to find.
- Intake leak causing lean burn : maybe somewhere way down low there's an intake leak. I had a P/S pump failure recently, so maybe the leaking fluid messed up a gasket or hose in a place that I can't easily find.

The current plan is to go through the whole intake system soup-to-nuts, down to the bare block, some time soon to really track down if it's a vacuum problem, intake leak, or what. BUT, recommendations and advice would be greatly appreciated.

Apr 15, 2010 | 04:39 PM

jackhild59

Rotary $ > AMG $

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From: And the horse he rode in on...

First of all, NOx is usually low on rotary's compared to pistons. Something basic is wrong.

Second, to set idle you need to check out the FSM (link in the sticky). S5 you need to jump the set idle jumper, then adjust the idle using the screw on the top of the intake. Don't adjust it without the set jumper! Then you will probably need to adjust the TPS as well.

Apr 15, 2010 | 05:05 PM

ericgrau

Clean.

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From: Huntington Beach, CA

Your HC and CO are also very low, which means you are running lean. Advanced timing is another less likely possibility. The forum FAQ on emissions gives this and a couple other possibilities. IMO EGR also fits. What kind of fuel management are you running? A stock NA ECU with all those exhaust upgrades and porting might do it, not sure.

A greater concern is the possibility of detonation which could make you lose an apex seal with only one good strong ping. This is rare in a non-turbo, but only because they usually run so rich (hence why emissions tend to be the reverse). Even if you are running lean I think retarding the timing should improve emissions and make detonation less likely but at the expense of power. It could be a temporary fix until you figure out the problem. High octane fuel might also be a temporary fix (though only as detonation prevention)

Maybe check your AFR ratio first to confirm that leanness is the problem and not one of the other possibilities listed in the FAQ.

Apr 15, 2010 | 05:19 PM

CrazyDude

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Joined: Jan 2002

Posts: 172

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From: Pasadena, CA

Stock ECU, it's a California one, too.

I didn't think that S5's had EGR systems? The timing is already very retarded just to pass this test.

For setting the idle, the screw on top of my throttle body is already screwed all the way in (or out?); adjusting it just raises the idle speed. TPS is adjusted to read 1.0v at idle.

I do have a TechEdge Wideband O2 sensor somewhere, I suppose I better install it. I guess I can also put a scope on my narrowband sensor and see if it's going into closed loop mode, but I assume that it'd be generating a fault code if it wasn't?

Apr 15, 2010 | 05:34 PM

arghx

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From: cold

Quote:

The timing is already very retarded just to pass this test.

that can raise EGT's. higher exhaust temps can correlate with more NOx.

Apr 15, 2010 | 05:45 PM

ericgrau

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From: Huntington Beach, CA

Correlation is not causation as they say. IIRC from my college class it's high combustion temps that cause NOx. Retarding the timing may roast your exhaust as more of the fuel burns there instead of your engine but it'll reduce the combustion temperature for less NOx. i.e., high combustion temps may lead to high exhaust temps, but high exhaust temps doesn't necessarily mean high combustion temps.

I dunno about the s5 but I thought every car had EGR thanks to the EPA. Though I'm guessing running too lean is more likely. Might as well leave the timing where it is to be safe until you figure out the issue.

Apr 15, 2010 | 06:17 PM

RotaryRocket88

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From: San Diego, CA

Quote:

Originally Posted by ericgrau

Your HC and CO are also very low, which means you are running lean.

The job of the ECU in closed loop is to put AFRs right around 14.7. It's supposed to be "lean". Under the cruising conditions of a smog test, this would be a good thing.

Quote:

Originally Posted by CrazyDude

I didn't think that S5's had EGR systems? The timing is already very retarded just to pass this test.

Correct. No EGRs on S5s. Mazda found a loophole in '89 I guess, but the FD ended up getting an EGR back in '92.

Quote:

Originally Posted by CrazyDude

I do have a TechEdge Wideband O2 sensor somewhere, I suppose I better install it. I guess I can also put a scope on my narrowband sensor and see if it's going into closed loop mode, but I assume that it'd be generating a fault code if it wasn't?

You probably wouldn't have passed the test if the 02 sensor wasn't functioning. And yes, there is a trouble code for this on S5s.

Closed loop mixtures are fairly meaningless (except for emissions & fuel economy), so I wouldn't worry much about the NOx numbers. Get the wideband working, and see how things are under load. That's where it counts. My last smog test had almost non-existent NOx levels, but in previous years with a junk main cat (and a faulty EGR valve), I've had NOx levels high enough to fail.

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Apr 15, 2010 | 06:26 PM

LargeOrangeFont

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From: OC, So Cal

My car is pretty similar to yours with my "smog setup"

Streetported s4 N/A
K&N intake
RB catback
Magnaflow 2.5 in cat with AIR injection
All stock smog equipment installed
Stock base timing
RTEK 2.0 (no tuning done in low RPM/low load areas)

I just smogged mine with nearly the same results. An exhaust leak will cause high NOx as well. I had a noticable exhaust leak during the test.

My "off road" setup is a header that eliminates the manifold and precats, a resonator in place of the main cat and the AIR injection blocked.

Also, when I bought my car the O2 was not connected and it passed smog.

Apr 15, 2010 | 06:26 PM

jackhild59

Rotary $ > AMG $

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From: And the horse he rode in on...

Did you screw the idle screw in without jumping the jumper? If so, the ECU will ignore the screw setting.

Possible that the timing marks are off due to the rebuild? You might verify the timing, restab the CAS etc.

A stock NA should not be running lean. The timing should not have to be retarded to achieve emissions compliance. Right now you seem to be chasing symptoms, but not the core cause. .When you figure it out, it is going to be very basic.

Apr 15, 2010 | 06:44 PM

#10

LargeOrangeFont

Fistful of steel

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From: OC, So Cal

Quote:

Originally Posted by jackhild59

Mine was running really lean under load for a long time. I could not figure it out and had to add 50% fuel with the RTEK to even get it close and it was still lean. It is better now after trying 3 different AFMs and finally finding one that fixed it.