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Vanaru 2.5 High NOx - failed emissions - Solved
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davevickery
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PostPosted: Mon Sep 05, 2016 5:33 pm    Post subject: Vanaru 2.5 High NOx - failed emissions - Solved Reply with quote

I have a syncro with 2.5 from 2001 Legacy that failed its first emission test due to High NOx. When you google high NOx, the most common thing that comes up is the EGR valve is clogged. But this year model engine doesn't have an EGR.

NOx is produced by high combustion chamber temps. I think it has to get to 2500 degrees and should not normally go above 1500. So what else should I look at?

Any ideas appreciated.
Dave


Last edited by davevickery on Mon Sep 12, 2016 4:54 pm; edited 2 times in total
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kamzcab86
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PostPosted: Mon Sep 05, 2016 6:09 pm    Post subject: Re: Vanaru 2.5 High NOx - failed emissions Reply with quote

davevickery wrote:
So what else should I look at?


Not Subaru-specific, just general items when NOx is high (running too lean):

-Vacuum leak(s)
-High idle due to vacuum leak
-Faulty/clogged catalytic converter
-Faulty oxygen sensor
-Timing is advanced too far
-Incorrect air-fuel mixture
-Dirty air filter
-Faulty ignition components
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sanchius Premium Member
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PostPosted: Mon Sep 05, 2016 7:44 pm    Post subject: Re: Vanaru 2.5 High NOx - failed emissions Reply with quote

How healthy is your cat?

Here's my notes on taking my Audi Cab through Colorado emissions a few years ago...
1 of the 2 cats was damaged, I replaced them both and it drastically lowered both HC & NOX

"My manual transmission Cabriolet was having trouble passing Colorado emissions.
The tests here are cheap, $25 for two tests, though at about 40min each test, the time cost adds up.
So I walked through the process incrementally, starting with the cheapest fixes first, and here's how it went...

Test 1: HC 1.7/1.2 Fail, CO 5.4/15.0 Pass, NOX 3.5/3.0 Fail (GPM Measured/Limit)

-> Clean EGR passageway New air filter, plugs, oil change & 1/4 tank of E85 (~$60)

Test 2: HC 1.5/1.2 Fail, CO 6.6/15.0 Pass, NOX 2.8/3.0 Pass

-> New O2 sensors (~$120)
-> This was just throwing parts at it as I thought the cats would be much more expensive than they turned out to be.

Test 3: HC 1.4/1.2 Fail, CO 7.6/15.0 Pass, NOX 2.5/3.0 Pass

-> Got a quote from local garage of $1200 to install new cats, no thanks...
-> Order a set of $157 cat+pipes from ebay (~$320) (for Manual Audi 90: Davico 16195 & 16198 49-state legal)
-> Since then saw that Rock Auto has them for $137 each
-> When installing new cats, notice that one of the old cats had a big dent in the bottom and all the matrix was gone.
-> Empty matrix chunks from the aft muffler...

Test 4: HC 0.5/1.2 Pass, CO 1.1/15.0 Pass, NOX 0.8/3.0 Pass

Lesson learned: Tuning will get you close and give incremental improvements, but good cats are necessary to fully pass."
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davevickery
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PostPosted: Mon Sep 05, 2016 8:18 pm    Post subject: Re: Vanaru 2.5 High NOx - failed emissions Reply with quote

sanchius wrote:
How healthy is your cat?
Thanks for the reply,
A new cat would probably bring the readings down. I've read some results besides yours where it also made a dramatic difference. But the problem is from what I read, and I could be wrong, high NOx is only created when the combustion chamber temps are way above the max they should be at, like 2500 degrees. You need to get to 900 degrees to burn efficiently and not foul plugs, but should not get over 1500 degrees. A good cat will transform NOx and bring down the numbers but won't address the high combustion temps.

The other difference is yours is a turbo right?, where the temps are usually way higher. But on my old 1.8T Vanagon I had a hollowed out Cat when I bought it and I passed emissions easily. So I don't want the cat to hide the problem.
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davevickery
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PostPosted: Mon Sep 05, 2016 8:26 pm    Post subject: Re: Vanaru 2.5 High NOx - failed emissions Reply with quote

kamzcab86 wrote:

Not Subaru-specific, just general items when NOx is high (running too lean):

-Vacuum leak(s)
-High idle due to vacuum leak
-Faulty/clogged catalytic converter
-Faulty oxygen sensor
-Timing is advanced too far
-Incorrect air-fuel mixture
-Dirty air filter
-Faulty ignition components

Thanks Kamz, I think I can rule out some of these because the engine is different. I miss that distributor, you could just twist it a bit for the emissions test. Timing for these are built into the ECU, same for fuel/air mixture. Doesn't even have an air flow meter. I have a scan gauge which is kind of fun so I can look at A/F mixture and it doesn't seem to be running lean. I had it tested for vacuum leaks when it was first put in, so I don't think that's it unless they are new. New O2 sensors too at conversion. The HC readings were medium so I don't think it is a lean condition, but I could totally be wrong, and I appreciate the reply and possibilities.

But I did get a new air filter and spark plugs and will get higher octane gas for the retest. I don't know the age of the plug wires, so I might just replace them too.
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PostPosted: Mon Sep 05, 2016 8:53 pm    Post subject: Re: Vanaru 2.5 High NOx - failed emissions Reply with quote

A blocked or restricted cat will raise combustion temps and not throw codes until the 02s start acting up. Pull the 02 and run a vacuum backpressure test. Or drop the cat and look through the honeycomb.
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PostPosted: Tue Sep 06, 2016 5:35 am    Post subject: Re: Vanaru 2.5 High NOx - failed emissions Reply with quote

davevickery wrote:
sanchius wrote:
How healthy is your cat?
Thanks for the reply,
A new cat would probably bring the readings down. I've read some results besides yours where it also made a dramatic difference. But the problem is from what I read, and I could be wrong, high NOx is only created when the combustion chamber temps are way above the max they should be at, like 2500 degrees. You need to get to 900 degrees to burn efficiently and not foul plugs, but should not get over 1500 degrees. A good cat will transform NOx and bring down the numbers but won't address the high combustion temps.

The other difference is yours is a turbo right?, where the temps are usually way higher. But on my old 1.8T Vanagon I had a hollowed out Cat when I bought it and I passed emissions easily. So I don't want the cat to hide the problem.

I don't know much about the 1st part other than I don't have any reason to believe that my combustion temps were non normal.

It's a mild, pure stock, non-turbo motor that I maintain as a reliable commuter car.
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narendra.vw
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PostPosted: Tue Sep 06, 2016 6:51 am    Post subject: Re: Vanaru 2.5 High NOx - failed emissions Reply with quote

sanchius wrote:
How healthy is your cat?

Here's my notes on taking my Audi Cab through Colorado emissions a few years ago...
1 of the 2 cats was damaged, I replaced them both and it drastically lowered both HC & NOX

Lesson learned: Tuning will get you close and give incremental improvements, but good cats are necessary to fully pass."


Very informative feedback. Thanks for that.

Does this hold good for Gas & Diesel?
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davevickery
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PostPosted: Tue Sep 06, 2016 10:02 am    Post subject: Re: Vanaru 2.5 High NOx - failed emissions-SOLVED Reply with quote

newfisher wrote:
A blocked or restricted cat will raise combustion temps and not throw codes until the 02s start acting up. Pull the 02 and run a vacuum backpressure test. Or drop the cat and look through the honeycomb.
Thanks Newfisher, you are right on about that but I looked through the Cat and the honeycomb is intact and I see the tpically point of light down the center when I hold it up.

Carbon build up seems possible, but I just did a half bottle of sea foam through the intake and the other half is in the gas tank now waiting to burn through that tank before retesting. If the timing wasn't set by the computer, I would strongly believe it was that. Perhaps the high octane fuel will fix this by itself. I will be getting it tested again tomorrow, so I will see with just the few things I did.

Since there is no EGR on this engine that simplifies a lot of things and it should run way way cleaner than vanagon levels. My 2002 Camry had .15 GPM NOx with a limit of 1.5. The limit on the Vanagon is 5.0 but the subaru engine is the same era as the camry so it's limit should also be 1.5 gpm, so NOx of 5.4 is way to high.

I think my other numbers all tell me that I am not running lean.


EDIT: I passed after putting on a new expensive california cat. I had put a used Emico vanagon cat on with the conversion. I don't recall the history on it but it looked o.k. There is a quite a difference in diameter between that and the new Magnaflow California cat.

In the process I learned a lot about NO emissions. believe engines that didn't come with an EGR system were designed to remove any NO through the cat. The other typical factors just aren't adjustable on a subaru, namely timing and a/f mixture (Unless you have a bat o2). I never did find out what normal pre-cat NO levels are but it's possible they go up when swapping a subi into a van with shorter intake and exhaust. Maybe that makes it run just a little leaner.

In any case, a new california cat (see van-cafe) remove 90% of my NO emissions. I did nothing else and went from 5.8 NO to .0.30. CO and HC also droipped by a factor of 10, so I easily passed the vanagon limits or new car emissions for that matter.

The numbers were so low, I am going to conclude that everything is fine and NOx reduction relies on a good cat. If I had just barely passed, I was going to keep looking but I am under 10% of new car emission standards, so I think I am good.
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