NOx, EGR, woe

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NOx, EGR, woe

Postby tigerdog » Thu 15.07.2021, 00:11

Knock me over with a feather, but I cannot find any reference to the EGR system in the forum.

Smaug is failing his California smog test due to high NOx emissions. Everything I've read indicates high NOx is produced at high combustion temperatures. EGR theoretically mitigates the issue by introducing a small amount of exhaust gas into the intake when NOx emissions might be high (i.e, part throttle, light load). Here's the rub: current test methodology requires measurements to be taken on a rolling road/dynomometer, in 2nd gear, at 15 and 25 MPH. In Smaug, 15 MPH is achieved at only 1625 RPM. I'm not sure there's enough vacuum to fully open the EGR valve. At low speed, it fails at 1135 PPM 835 max allowed; at higher RPM (2600) it passes at 709 PPM/ 779 max. Two years back, it barely squeaked by the same test 832/885. Looking back on previous tests, I see the 15mph test was run by some testers in 1st gear, which put RPMs up around 2600. This apparently now violates the testing standard.

I've read multiple, conflicting suggestions for reducing emissions on various forums. Here, where the community is both educated and thoughtful, I'd love to open a couple of topics:
    - Why is the EGR vacuum takeoff right at the throttle, while every other vacuum takeoff is at the back of the engine? Would moving it have the effect of increasing available vacuum to the EGR valve?
    - Fuel octane rating on combustion temperature and NOx creation. Simply asked, is higher octane fuel beneficial or detrimental to NOx formation?
    - Any other California owners, would you please post your most recent emissions scores? I'm trying to find out how much might be attributable to Smaug's, ahem, interesting hardware.
Please, brilliant friends, discuss.
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Re: NOx, EGR, woe

Postby CalElan » Thu 15.07.2021, 05:27

Mine wasn’t put on a rolling road at the last test.
It was heat cycled a couple of times, run until the fans kicked on to ensure the cat was up to temp and then I believe the exhaust was probed.
Job done.
Is the rolling road test new or are they doing it because it looks none standard under the hood?
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Re: NOx, EGR, woe

Postby CalElan » Thu 15.07.2021, 05:31

Also, the sticker under the hood shows how the plumbing should be connected. If you move the EGR take off will it fail the visual plumbing inspection?
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Re: NOx, EGR, woe

Postby CalElan » Thu 15.07.2021, 06:03

These are listed as the 3 types of test administered.
TSI Test – the two-speed idle test measures through the tailpipe to determine the level of emissions while the vehicle is in idle. This measure is taken both at low and high speed. The TSI test typically applies for older vehicles, although your location also plays a factor. If your vehicle is registered in a Basic area, this test will be required.
ASM Test – the acceleration simulation mode test measures is typically used with very old vehicles. This test incorporates a drive-on dynamometer which measures exhaust emissions while the vehicle is being “driven.”
OBDI Test – the on-board diagnostics test measures data provided via your vehicle’s computerized diagnostics system. This test is applied to any vehicle from 2000 and up.

So mine is given the TSi test.. sounds like yours is the ASM?
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Re: NOx, EGR, woe

Postby GeoffSmith » Thu 15.07.2021, 11:03

What a bummer! Looks like higher octane fuel might improve things (see below) but it's nowhere near conclusive. I wonder what effect more or less ethanol has on the figures. I wonder if a leaky EGR valve would help. Do you want to move State, in which case how much do you want for Rimini. :wink:

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https://www.sciencedirect.com/science/a ... 0218312128
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Re: NOx, EGR, woe

Postby tigerdog » Thu 15.07.2021, 15:05

CalElan wrote:So mine is given the TSi test.. sounds like yours is the ASM?

Yep. San Diego area requires a full ASM at a STAR-approved station. It's the price we pay for living in paradise. Did you happen to save the emissions result page from your test?
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Re: NOx, EGR, woe

Postby tigerdog » Thu 15.07.2021, 15:10

GeoffSmith wrote:What a bummer! Looks like higher octane fuel might improve things (see below) but it's nowhere near conclusive. I wonder what effect more or less ethanol has on the figures. I wonder if a leaky EGR valve would help. Do you want to move State, in which case how much do you want for Rimini. :wink:

https://www.sciencedirect.com/science/a ... 0218312128


We've one station here that sells genuine, California-approved 100 Octane fuel, so that's what goes in Smaug's tank at his annual fill-up (I really need to drive the car more!) I've seen other cars surreptitiously replumbed to force the EGR open (bypass the solenoid valve) though that's not preferable to make it "just work."

As for Rimini House see below
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Re: NOx, EGR, woe

Postby FunElan » Thu 15.07.2021, 16:56

My Elan isn't in California yet, so I can only speak to my experience smogging my e36 BMW in Los Angeles. It failed the same exact way yours did. High NOx at 15 mph. The tester told me I needed a new catalytic converter. I've gotten the car to squeak through by knowing good testers, but also treated vacuum leak symptoms. I changed the O2 sensor for a new one, replaced all rubber vacuum lines, the Crankcase vent (not sure if our Elans have a valve for this), and recently changed the Mass airflow sensor, which are known for 'slow-failing' over time.

We'll see in 2 years if I really do have to replace the cat, I just barely snuck by this time. I have contingencies just in case. Doug, since you only fill it up once a year, perhaps you could register Smaug as a Historical vehicle, which would limit you to 5000 miles a year. It also gives you smog exemption, last I checked. The vehicle must of 'historical interest' and at least 25 years old.
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Re: NOx, EGR, woe

Postby CalElan » Thu 15.07.2021, 17:00

tigerdog wrote:
CalElan wrote:So mine is given the TSi test.. sounds like yours is the ASM?

Yep. San Diego area requires a full ASM at a STAR-approved station. It's the price we pay for living in paradise. Did you happen to save the emissions result page from your test?


I can’t find the paperwork - but I will be smog testing again in the next month.
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Re: NOx, EGR, woe

Postby Simon_P » Fri 16.07.2021, 20:49

tigerdog wrote:Why is the EGR vacuum takeoff right at the throttle, while every other vacuum takeoff is at the back of the engine? Would moving it have the effect of increasing available vacuum to the EGR valve?
The plenum takeoffs are using engine pumping vacuum at closed throttle to empty vacuum tanks for use later... When it runs out the heating doesn't work. The throttle edge port is using venturi generated vacuum at part throttle, the EGR operates at part throttle so the vacuum can be tuned to the EGR requirement for a cheap simple and reliable system. - Make sure it is clean.

tigerdog wrote:- Fuel octane rating on combustion temperature and NOx creation. Simply asked, is higher octane fuel beneficial or detrimental to NOx formation?
I'll rephrase your question. What is the effect of fuel composition on NOx formation in an SI gasoline engine during a california emissions test... Simply answered - No idea there are too many variables.

Higher octane fuel burns more slowly so it may be hotter longer or it may be instantaneously cooler.

NOx reduces as engine speed increases due to the shorter time period that the combustion gasses are at highest temperature.

Check the ignition timing - NOx increases with advance.

What is the intetesting hardware? Edit oh I see I wouldn't worry about that lot.
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Re: NOx, EGR, woe

Postby tigerdog » Sat 17.07.2021, 00:35

Simon_P wrote:What is the intetesting hardware? Edit oh I see I wouldn't worry about that lot.

visit LEC forum, search "green monster" and/or "smaug" shhhh......
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Re: NOx, EGR, woe

Postby FunElan » Sat 17.07.2021, 18:15

I had a friend retard the timing in an old Audi to help him pass smog. Set it right back afterwards. I wonder if this is a method that's available here.
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Re: NOx, EGR, woe

Postby tigerdog » Sun 18.07.2021, 17:02

FunElan wrote:I had a friend retard the timing in an old Audi to help him pass smog. Set it right back afterwards. I wonder if this is a method that's available here.

Timing on the Elan is under command of the ECU, but I believe the ECU simply advances or retards around the base timing. If this is correct, then it should be possible to retard the base timing and shift the entire timing curve relatively. Right now, the plan is
- refit the cold air intake hose and snorkle. Hopefully this will lower combustion temp by feeding colder air.
Previous owner had removed it in favor of a "filter on a stick" Top End Performance intake, removed and restored to the original dustbin/trash can to pass visual inspection.
- fit a toggle that runs the cooling fan continuously. rolling road test has no provision for cooling, so the engine sits at the top of the temp range with fans kicking in and out.
another attempt to reduce combustion temps.
- increase vacuum at EGR solenoid through careful cleaning of entire vacuum circuit.

Joy and fun. Some times, I think I'd have been better off with a bone-stock example. But only sometimes :)
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Re: NOx, EGR, woe

Postby GeoffSmith » Sun 18.07.2021, 19:56

Thinking out loud after seeing this and thinking that a richer mix might help you:
Image
Increase the resistance of CTS with series resistor to make it appear colder than it is, thereby increasing fuelling… but it probably won't work if it's closed loop. This may also defeat any possible benefits of different fuels and/or timing.
Would field service mode force it open loop which might help you? Can you set it into service mode remotely (say via an App and BT ES interface :wink: ) or do you hand over the car and not see it until the job is finished?
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Re: NOx, EGR, woe

Postby tigerdog » Sun 18.07.2021, 21:02

GeoffSmith wrote:Increase the resistance of CTS with series resistor to make it appear colder than it is, thereby increasing fuelling… but it probably won't work if it's closed loop. This may also defeat any possible benefits of different fuels and/or timing. Would field service mode force it open loop which might help you? Can you set it into service mode remotely (say via an App and BT ES interface :wink: ) or do you hand over the car and not see it until the job is finished?


I think a richer mixture is pretty easy to obtain on this car. Simply pulling the battery terminal to reset the ECU, without going through the learning phase, should do the trick. That said, your idea of a series resistor is, er, irresistible. It would do the trick without pulling the thermostat. If I recall, the CEL flashes when in service mode - that visual would cause an immediate test failure... but I might just double-check.
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Re: NOx, EGR, woe

Postby dapinky » Mon 19.07.2021, 18:46

Whilst I ill get my excuse in early, after another 12 hour shift, it *may* have some merit....

.... would changing the spark plug gap induce a richer mixture , or would incomplete combustion make things worse?

(just trying to think of another easy way to make a temporary change which wouldn't be visibly obvious)
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Re: NOx, EGR, woe

Postby tigerdog » Tue 20.07.2021, 01:44

dapinky wrote:... would changing the spark plug gap induce a richer mixture , or would incomplete combustion make things worse?)

Richer will raise the other bad stuff CO, unburned HC, etc. The real problem is not having access to a sniffer with which to validate the changes.
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