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hello friends,

so my car failed smog, then i worked on a bunch of things, then i waited a year, and then it failed again. i want to know what else i should do.

it is a 1995 manual g20t with 294000 miles. it runs wonderfully. it is smooth, quick, and rev-happy like any healthy g20 should be. the engine, intake, and exhaust are completely stock and original.

here is what happened:

1. i didn't have to smog my car for over seven years because of where i lived

2. december 2016
car failed smog, no surprise


3. december 2016
- completely revamped egr system: removed, cleaned, and tested egr valve; removed and tested egr bpt valve; fixed broken hose on bottom of bpt; diagnosed and replaced faulty egr solenoid; tested egr functionality using factory service manual procedure; no more egr check engine light.

- replaced both oxygen sensors with new oem sensors.

- replaced crappy copper spark plugs with oem ngk platinums. (woops i meant to use platinum last time)

- cleaned maf and tested with multimeter using factory service manual procedure.

- reset timing to 15 degrees. (it was at 13 somehow)

- cleaned k&n air filter with their kit.

- didn't replace cap and rotor, i replaced them in 2015-16 with oem.


4. all of 2017: engineering school ate my life and my g20 sat in the garage unregistered while i biked everywhere. (sorry beautiful friend)

5. december 2017
g20 failed smog again. (worse this time)


6. ???????

what should i look at? i don't know what to work on or replace. the only things i can think of are the catalytic converter being worn out, or a leaky injector, or a vacuum leak.

someone suggested having a shop figure out for me what is causing the high numbers. that would be the first time i ever let a shop touch this car.

thanks for your suggestions
 

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Well if you are against throwing a ton of money at it, which probably includes any option of "letting someone else look at your car." I would say, look into using some additive (like this one) to see if you can pass the test.

I also recommend that if you suspect any injector issues, that you try to address right away. Sure diagnostic ecu equipment could help you to evaluate fuel trims to see if you can narrow down an actual injector related issue. But I think the best way to have 100% confidence in a high mileage car's fuel injectors, is to pull the injectors, then to have them flow tested and sonic cleaned. Did business a few times with a guy named Bill a few years back who owns Mr. Injector. Actually just picked up a P11 with 150k a few weeks ago, and probably going to have the same service completed soon on all 4 injectors for this car too.
 

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NOX is usually a mixture of things, most notably:

  • O2s
  • CAT
  • Injectors

In my experience, with the stock ECU, I actually rolled ignition timing back to help lean it out, and a new cat if your using an older one is gonna be needed. It could be finally just dead (happened to me over a 2 year stint).

High HC is almost always due to a lean mixture, either by injectors or bad timing, by what you mentioned in the chat, it's likely an injector is bad.

I would get a new CAT, new injectors, and make sure with a timing gun its actually set to the right timing (not ECU correcting).

As far as the CAT is concerned, your best bet is to get a Magnaflow California rated cat, they have the highest platinum content. If your still stock exhaust, https://www.magnaflow.com/products?partNumber=448707

If you aren't, Magnaflow makes these without the flanges and you can buy any sizing you need (thats what I did) and got flanges welded on.
 

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^ I was going to recommend a new catalytic converter as well. Other than that and cleaning your injectors (two tasks that can cost a lot of $$$, I know...), you can try using premium gasoline with Redline SI-1 cleaner. Go through half a tank of that and, with your new cat and/or injectors, I would hope that you could pass the test. I have to pass mine next month! :nervous:
 

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crappy copper plugs? this guy. did you close that gap if not its at 044 on platinum . resistance test the wires and coil? the capacitor on the dizzy was old and shorted on mine and was causing buildup inside the cap . clean the spark plug threads in the head and clean your grounds or add a ground kit . your cap n rotor is 2 years old replace it. i bought the "OEM" and they lasted 15000 miles and when it went to the impound lot corrosion kicked in fast. take the dizzy cap off and look at it and rotor. DONT touch any electric connection with your dk beaters. gumout with PEA is good too. Also throttle position check too.
 

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Smog testing sux... I won't even touch a 96 or newer G20 here in Illinois now because 95 and older here means no smog testing EVER.

I'm sorry to hear about your issues and finger's crossed its a simple injector and fuel injector cleaner fix.. gluck!
 

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Mines having the same issue. It starts off in the green, but once it stays at that speed for smogging, itll jump right on over to fail. Somethings running too hot in my engine, and im pretty sure its cuz theres too much carbon buildup in my cylinders thats creating the extra heat. If NOx is your issue, somethings too hot. Cant be the cat if everything else is running fine. Try O2 sensors, maybe your sensors are throwing your injectors off, running either too rich or too lean. Im still working on mine so ill let you know what happens ?
 

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I suggest cleaning all emission related stuff before you start to buy parts could be something as a cracked hose and a bad spark plug wire. If you have a ohm reader put the leads on opposite end of the spark plug wire and see if the resistance holds, this way you will know for sure if you have a bad wire.
 

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Just l had a similar smog check issue, and found a crack in the intake boot, between the MAF ( air filter) and the throttle body. The crack was hiding in the accordion portion of the intake boot. Patched it with high temp gasket goop, and passed no problem.
 
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