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Old 05-06-2011, 06:54 PM   #1
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Default Non Miata perpetually failing emissions, need MT brainpower!

Here's the squeeze:

94 Sentra (ga16de) with a Stillen pop filter, 4-2-1 header (the qg18 header) with egr in #4 runner and O2 in #3 runner (the stock exhaust manifold is a 4-1 with the O2 at the collector).

First time I failed my numbers were this:

HC 198 CT limit 188
CO .03% CT limit 1%
NOx 1112 CT limit 2188

Did the test after a short city drive there (about 20 minutes stop and go at about 35mph)

Timing is at ~8 degrees. The plugs were, and still are, a light tan color with minimal carbon on them (only on cylinder 1 and 4). I replaced all 3/16 vac lines, new ntk O2, new ngk wires, ngk plugs gapped to .43 with about 5k, replaced the cap and rotor about 5k ago, and checked the resistance for the coil (which was 1 ohm and 13.3k ohm). I also reset the ecu and it threw no cel's. The water pump leaks coolant as an added bonus. Then I went back to the Emissions place and failed again. Here are the numbers:

HC 326 CT limit 188
CO .03% CT limit 1%
NOx 2136 CT limit 2188

Car was hot (just finished a 30 minute highway trip) for this one.

After replacing a bad injector, cat (magnaflow), and fixing the exhaust leaks the car runs 100% better. I also bumped the timing up from 8 degrees to 12 degrees and I drove the car for about 75 miles 50/50 city/highway after doing all the work. Here are my numbers:

HC 162 CT limit 188
CO 1.22% CT limit 1%
NOx 1990 CT limit 2188

Then I set the timing to 10 degrees and went again, my numbers went down...but I still didn't pass. Here are the numbers for this one:

HC 161 CT limit 188
CO 1.11% CT limit 1%
NOx 1667 CT limit 2188

So it seems turning my timing back will get me to pass but that won't address the real problem (CO going up so much when I replaced the bad injector, catalytic converter, and bumping my timing up).

I also verified the resistances of the injectors, coolant temp sensor, and coil to be within spec for proper functionality as an added bonus.

What do you guys think could be going wrong?
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Old 05-06-2011, 07:09 PM   #2
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Its possible that something is causing you to run slightly rich. If you're failing by such a small amount and you've replaced everything under the sun, I'd say PCV, do an oil change, heat the **** out of the cat and try again.
Are you sure that injector is good?
Retarded the timing and CO is going down....whatthefuckamireading.jpg
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Old 05-06-2011, 07:20 PM   #3
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PCV was also changed...like 7K ago but I'll throw another in.

I verified the resistance of the injectors and when I installed the good one the car ran much better...only thing that could have gone wrong from the injector is the seal didn't seat properly and I am getting too much fuel in there. I'm going to check the plugs to be sure.

I retarded the timing and EVERYTHING went down.
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Old 05-06-2011, 10:17 PM   #4
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So reading the plugs everything looks to be ok. All plugs are a nice tan color (porcelain, grounding strap, and top two threads) so I am going to let go of the bad #2 injector seal. Anybody else want to weigh in?

Really don't feel like taking a pic of my plug but this is about what they all look like except they are devoid of the timing indication on the grounding strap (pretty much the same color all the way to the threads):
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Old 05-06-2011, 10:23 PM   #5
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My buddy passed his emissions in his 87 monte carlo by literally retarding the timing until the thing would BARELY run... to the point where he did the change in the parking lot. Retarding timing raises one of the values but lowers the other 2, cant remember which is which tho.

Seafoam the **** out of it?

Thats all I got. . .
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Old 05-06-2011, 10:38 PM   #6
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I thought about seafoaming it (have a can sitting on the shelf actually) but I am wondering if it will make some other problem apparent and cause me to fail some new and exciting way.

I've already paid $80 to the emissions guys and $20 to the state for my emissions being expired. I really want tomorrow to be the last time I pay for this ****.
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Old 05-06-2011, 11:15 PM   #7
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drop the highflow cat and replace with stock. preheat car. retard timing.
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Old 05-07-2011, 12:26 AM   #8
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O2 and CO2 numbers are critical for troubleshooting.

See here:
http://www.autoshop101.com/forms/h55.pdf
http://www.autoshop101.com/forms/h56.pdf

Last edited by JasonC SBB; 05-07-2011 at 12:43 AM.
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Old 05-07-2011, 01:08 AM   #9
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Great guys. Thanks for the input (especially those two links). Tomorrow I'll be: checking my evap stuff, getting a new pcv, pushing my timing back a couple more degrees, and double checking my sensors.

Or could all this fail be coming solely from the magnaflow cat?
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Old 05-07-2011, 03:01 AM   #10
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Didn't I just say you need to post the O2 and CO2 numbers?
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Old 05-07-2011, 09:27 AM   #11
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I don't have either number. I guess I could get the voltage from the O2 sensor and try to come up with something from there.
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Old 05-07-2011, 10:07 AM   #12
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I am so happy that I live in a place where you don't even need a basic inspection.
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Old 05-07-2011, 12:16 PM   #13
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Quote:
Originally Posted by astroboy View Post
I don't have either number. I guess I could get the voltage from the O2 sensor and try to come up with something from there.
Too many variables, if you have any kind of exhaust leak post o2 sensor, it'll skew the o2 % readings, but not the sensor itself.
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Old 05-07-2011, 12:18 PM   #14
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Quote:
Originally Posted by astroboy View Post
I thought about seafoaming it (have a can sitting on the shelf actually) but I am wondering if it will make some other problem apparent and cause me to fail some new and exciting way.

I've already paid $80 to the emissions guys and $20 to the state for my emissions being expired. I really want tomorrow to be the last time I pay for this ****.
I can't see that happening honestly. If theres actually **** on top of your pistons, seafoaming it will bring NOx down. Not that you care, your NOx cut off numbers are RIDICULOUSLY high. In CA, my cutoff number is something like 800.
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Old 05-07-2011, 12:38 PM   #15
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Quote:
Originally Posted by astroboy View Post
I don't have either number. I guess I could get the voltage from the O2 sensor and try to come up with something from there.
That won't tell you if the O2 sensor is false reporting O2 content.
Besides narrowband sensors can't distinguish between very rich and slightly rich or slightly lean and very lean.

You need to go get it measured with ALL 5 GASES showing.

If your O2 is very low the engine is running rich and the cat is healthy.
If O2+CO2 is high you have an exhaust leak, fresh air is contaminating the exhaust gas seen by the O2 sensor.
If your O2 is high but O2+CO2 is normal you are running lean and this is causing your high NOx; however this usually comes with low CO.
If your O2 is normal and CO and NOx are high, your cat is weak - it should be taking CO and NOx and turning it into CO2 + N2.

You didn't read the PDFs, else you'd have gone and had all 5 gases measured.

Without O2 and CO2 you are shooting in the dark. Like the bad old days of tuning without a WBO2.

Last edited by JasonC SBB; 05-07-2011 at 12:51 PM.
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Old 05-07-2011, 02:46 PM   #16
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******* failed again. Turned the timing back to 8 degrees, changed the oil, put in a new pcv, sealed any exhaust leaks that could possibly exist, and verified the O2 was working properly (voltage went from.18 to .86 when revving the engine). Here's the fail:

HC 238 CT limit 188
CO 1.10% CT limit 1%
NOx 1546 CT limit 2188

I am going to start looking for a shop around here that can analyze the exhaust for 5 gasses (seeing how emissions shops only do 3).
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Old 05-11-2011, 01:50 AM   #17
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FWIW all the emissions printouts here in CA show 5 gases.

Quote:
voltage went from.18 to .86 when revving the engine)
http://www.autoshop101.com/forms/h58.pdf
page 5
It should dither above 0.55 and below 0.4
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