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Old 08-08-10, 04:11 PM   #1
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Failed smog pre test. High Nox

Hey folks I have a bit of a problem now. I failed a smog pre-test On my 90 n/a. Everything else is fine but my NOx it thru the roof. Either I have alot of carbon build up or my engine is on its way out. Im thinking its the carbon build up. Whats recommended to clean it? Steam cleaning? Seafoam? The stuff Mazda sells for 50 bucks a bottle to clean the engine? Also the tech said my engine is ping-ing. Sigh* What to do next?
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Old 08-08-10, 07:14 PM   #2
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Check the FAQ section. Their is a sheet there that will give you some insight!
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Old 08-08-10, 07:17 PM   #3
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Nox is ussually due to high cylinder temps, the EGR system is designed to help reduce Nox, i'd say your EGR valve is either Inop, or blocked with Carbon. You'll need to remove it and clean it if it still good.
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Old 08-08-10, 07:18 PM   #4
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Cylinder temps or in this case, chamber temps. lol.
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Old 08-08-10, 07:25 PM   #5
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i've done nearly back to back smogs on the S4 na's and NOX goes WAY up if the timing is advanced.

takes 2 minutes to check

jdrift: s5 NA has no egr valve...
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Old 08-08-10, 07:53 PM   #6
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My car is having trouble passing emissions, but I have new spark plugs, filters, cats, etc. What do I do?
Click the image to open in full size.
and:
J-rats Recipe for cheating emissions if its ABSOLUTELY necessary:

1. Turn variable resistor to full lean, or as lean as you can get and still run.
2. Trick ACV into pumping air to the cat all the time by removing the FORWARD UPPER vac hose, and capping it.
3. Run 87 octane
4. Run your tank down till your almost empty.
5. 2-3 bottles of alcohol in the tank. Drive VERY GINGERLY to the emissions station.
6. Once you pass go, DIRECTLY to a gas station and fill up with regular unleaded.
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Old 08-08-10, 07:56 PM   #7
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i've done nearly back to back smogs on the S4 na's and NOX goes WAY up if the timing is advanced.

takes 2 minutes to check

jdrift: s5 NA has no egr valve...
Nox controled through timing then on that engine..?
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Old 08-08-10, 08:26 PM   #8
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2. Trick ACV into pumping air to the cat all the time by removing the FORWARD UPPER vac hose, and capping it.
Which one is that?
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Old 08-08-10, 10:57 PM   #9
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I have no idea and would have to look at the vacuum diagram to figure it out. The stuff I posted is from the FAQ section which I copied and pasted.


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Which one is that?
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Old 08-09-10, 12:59 AM   #10
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Click the image to open in full size.

I believe that's calling for removing the vacuum hose from the switching valve in the ACV. It might be the light blue vacuum line on the ACV in the diagram, but I can't be sure.

Click the image to open in full size.

The switching actuator is designed so that when vacuum is applied to it, airpump air will flow to the exhaust ports (port air) rather than directly to the cat. Normally at idle the engine vacuum will open switching valve and the air will go to the exhaust ports, before the O2 sensor. That's why if you hook a wideband to a 7 with emissions it will read super lean at idle. When you disconnect that hose from the switching valve it will remain closed and airpump air will instead flow to the cat (you will probably have to plug that hose you disconnect).

Click the image to open in full size.
That's for the FD, which is a bit more sophisticated, but you get the idea.


From the factory, the ECU will decide when it's time for air to flow to the cat. At this time it will engage the switching solenoid and the solenoid will cut vacuum to the switching actuator, which is the equivalent of disconnecting the hose. So technically you could put the ground wire on the switching solenoid directly to ground all the time and it would accomplish the same thing.
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Failed smog pre test. High Nox-s5_vacuum_routing_na-jpg   Failed smog pre test. High Nox-acv1-jpg   Failed smog pre test. High Nox-acv2-jpg  
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Old 08-09-10, 07:27 PM   #11
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eh, everyone is making **** overly complicated. my old 90 gtu passed with almost 0 emissions, because the cat was good. more than likely that cat is getting old and just not wanting to clean up the gasses.
funkjaw and myself both fucked with the timing as much as we could, retarding it and advancing it as much as possible and sat there and watched the nox not really change.
you guys can try all your voodoo tricks and **** that doesnt work, at the end of the day, its pretty much time to replace the cat, or spend hours and hours trying **** to squeek it by.

Lloyd
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Old 08-09-10, 07:42 PM   #12
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Lloyd,

No one said to use any tricks to pass smog here. The information I posted is from the FAQ section and is reference material.

You are correct that 90% (approx figure) the catalytic converter is bad. Their are other factors such as fuel issues, ignition issues, restricted air filter, etc.. However if the Air injection system is not working then no matter how good or if the catalytic converter is new it will not pass. There are also other factors that even if the the catalytic converter is good or brand new it will not pass.

Ones that I personally know about.

Air exhaust check valve bad allowing gasses to come back into the intake manifold.

AFM incorrectly calibrated on S4 or S3 engines. S5 is different Animal and no personal experience on that one.






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eh, everyone is making **** overly complicated. my old 90 gtu passed with almost 0 emissions, because the cat was good. more than likely that cat is getting old and just not wanting to clean up the gasses.
funkjaw and myself both fucked with the timing as much as we could, retarding it and advancing it as much as possible and sat there and watched the nox not really change.
you guys can try all your voodoo tricks and **** that doesnt work, at the end of the day, its pretty much time to replace the cat, or spend hours and hours trying **** to squeek it by.

Lloyd
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Old 08-09-10, 09:23 PM   #13
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my friend and i have 2 identical 87 gxl's, they are same color, ABS, made 1 month apart, etc etc.

anyways, his has a newish FACTORY main cat in it, mine is the original 75k unit.

mine all stock, blew 8ppm hc's, 0.05 co, and nox was 55

his blows similar HC and CO numbers, but his nox is in the high 600's.

the difference? his timing is advanced...

failing for NOX is weird though, usually its HC's, but first thing to check is to make sure the air pump air is going to PORT AIR like it should

http://foxed.ca/rx7manual/manuals/Tr...ol_Systems.pdf
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Old 08-09-10, 10:21 PM   #14
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Failing NOx on a rotary is strange. Highly advanced timing on a piston driven engine would cause this easily, but a rotary has a long and fairly cool combustion process considering the length of the combustion chamber area. My STOCK cat which has 163k miles on it passes emissions with flying colors. Maybe I am a minority but cat replacement wouldn't be the first on my priority list when it comes to NOx. Highly advanced timing and really lean conditions are the only thing that could cause high NOx, and if your timing was advanced that far, you would have lost an apex seal by now.

I would hook a wide band up to it first before throwing money at a cat.
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Old 08-09-10, 10:58 PM   #15
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Well I could always slap my stock exhaust back on. Complete with pre-cats to the stock mufflers.
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Old 08-10-10, 12:12 AM   #16
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Just recently went through this. Good CO and GC's. Had a vac leak due to a leaky twin scroll actuator line. But any leak would do it. I had to confirm it with a wideband. Vac leak causes it to run lean, high combustion temps result in high NOX. It didn't make any difference to the aftermarket boost gauge so it may take some detective work to find it. Hope this helps.
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Old 08-22-10, 12:36 AM   #17
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Mmm I checked my CAS and it turns out it wasnt stabbed in correctly. Odd I don't remeber ever adjusting it. I think one of my friends did. mmmm Now it idles and feels alot smoother. And feels very familiar like my first rx7. Which was very smooth and had a motor with good compression.
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Old 08-22-10, 12:36 AM
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