Urgently need help with ca smog and high Nox

[crzycrkr]

I have an 89 240sx SOHC and am having a hard time passing smog again. Car has 241,xxx and runs great. my smog test shows RPM %CO2 %O2 HC(max/ave/meas) CO(max/ave/meas) NO(max/ave/meas)15mph 1726 14.7 0.4 118/31/38 0.75/0.10/0.03 799/237/47625mph 1733 14.6 0.3 93/20/20 0.63/0.09/0.09 738/199/1207Plugs have just been replaced and old ones were tan all around. new oil, fuel filter, timing is good, maf and air filter cleaned. The guy doing the smog check seems to think the car is running lean to cause the nox to be high, but everything else to be low. Checked the vacuum to the egr and the egr itself and both are fine. I am out of ideas as to what this could be and I really can't afford to pay someone to figure it out for me. Can someone tell me exactly how to check the o2 sensor and injectors with a meter? I am not to good with electric, so idiot terms would be greatly appreciated. Any other ideas what this could be? I am out of time on this, so help would be greatly appreciated.Thanks

[smokerider]

that over mileage for a 240 but go to tech pages they show you what u need to know.to check 02 u go through self test on the ecu.sounds like u need to replace the injector. have u check ur timing chain and chain guide lately?holla back

[crzycrkr]

Chain and guides were replaced about two years ago. The self test on the ecu never seems to turn up anything, which is why I borrowed a meter. What do you mean by that over mileage for a 240?Thanks for the reply

[modulation]

I just went threw this myself.zerothread?id=324981

#1. Is the exhaust stock? Has it been changed out?(perhaps a leak)

#2 check to make sure EGR valve is working

#3 you are so close to passing, you can try taking your timing down by 3 degrees

#4 run the lowest octane that you can for the test

#5 If you haven't replaced your o2 sensor lately do so, it's cheap, easy and could be causing you to fail.

[crzycrkr]

1 Exhaust is stock and cat was replaced a couple years ago2 EGR is working 3 Tried that and it helped a little. Is the sohc a non interference motor?4 was running 87thats why I was wondering about how to test it with a meter in case it is out of whack a little. Comp is not throwing any codes.

Thanks for the reply

[crzycrkr]

I am also kind of confused as to why I passed nox at 15 easily but at 25 my measure was too high even though the average was lower.

[silpena]

hmm i had ur same issue a while back. I did everything and my timing was on. I passed 15mph but could not pass 25mph the nox levels just sky rocket. Comes out my timing was not on. IDk how i screwed it up but i guess i was 180 off or something... idk but o2 sensor could be it.

[crzycrkr]

Timing is definitely good. Still wondering how to check the O2 with a multimeter

[Rucca]

You need to test the voltages while it is running to see if the voltage is changing quickly enough. The ECM has an oxygen sensor test mode (Diagnostic Mode 2) I think that allows you to test it. Procedure is found in FSM under engine controls.

[crzycrkr]

Thanks you. Will check that out tomorrow. THe guy who ran the smog test said he thought I was leaning out and that was why the nox was high. What should I look for in regards to the? Thanks for the help

[kineone2010]

This may be a possible easy fix, Change your o2 sensor, drive your car for a good hour before testing to ensure the cat is at hottest temp, do NOT turn car off while waiting for testing. Born and raised in So-Cal, ( but now build SCCA Sm in TN and work as a mechanic. If this does not work, are you located near Yorba Linda?

[crzycrkr]

O2 sensor is new. Cat is working fine, Egr is working fine. I'm not too close to yorba linda, why? The smog tech still thinks I am running lean. The ecu is not throwing any codes. I think I am going to need to start testing other sensors. Where should I start? How can I check A/F ratio.THanks for the response.

[modulation]

O2 sensor is new. Cat is working fine, Egr is working fine. I'm not too close to yorba linda, why? The smog tech still thinks I am running lean. The ecu is not throwing any codes. I think I am going to need to start testing other sensors. Where should I start? How can I check A/F ratio.THanks for the response.

First smog tech's don't know ****. That's why they are smog techs.My smog tech said I was running lean too, I simply had an exhaust leak.

Try and get the emissions test done when your car is "cool."Most of the time the smog tech's will rev the **** out of the car and/or let it idle for a while before giving it a test. This is good at heating the catalytic converter up to burn more hydrocarbons, but you don't have that problem you need cylinder temps to be lower..

1. I'd go to a different shop, you never know if he's ****ing you.(I've heard smog repair shops advancing timing etc. just to make simple $100 "repairing" the car.)

2. Tight bolts that go from manifold to CAT.

3. Take out EGR tubes and clean them.

4. CRC Guaranteed to Pass Emissions Formula

5. Colder plugs?

6. Smaller plug gap...

My numbers looked like yours, I barely failed at 15mph but failed hard at 25mph. I had a exhaust leak before the cat.

[crzycrkr]

The tech isn't screwing me. I know him and it is a test only shop and he doesn't charge me for pre test or re tests. I'll recheck my exhaust again, but I don't hear an exhaust leak. Egr tubes are clear, I did that already. Would dropping the gap down slightly make that big of a difference? If it will then I will give it a shot. I considered the colder plugs and will probably be doing that next. We got it to pass, but I still want to find out if I am running lean and fix the problem. Which still brings me back to my question of how can I check the air/fuel ratio and what sensors should I start testing?THanks

[onosqv]

Only way to really check ur afr is to get a wideband o2 sensor -> which you will then need to use one where it will generate an analog signal for the ecu, or tap the header somewhere for a plug...

The stock o2 sensor will only give you very very broad rich/lean conditions - you can get the broad range testing routine from the FSM.

Even then, just seeing ur afr isn't going to help you fix anything since you are basically stock w/ stock ecu.

[Cone Junky]

How do you know the EGR is working completely? These engines are known to clog one or more of the EGR ports. So some ports don't get any EGR gas (raising NOx) and others get too much (increasing all emmisions).

I went from 1700 ppm of NOx to 140ppm with a few simple remedies-

ANY exhaust leak before the cat (huge NOx effect)

Fuel injection service (Seafoam or ?)

Cleaned EGR ports (requires taking off upper intake)

Colder plugs (dealers carry them)

Set timing to minimum (13 deg) spec

And of course- Run a complete tank of Chevron Supreme

[cesarnono13]

You could drop the exhaust, dril some holes on the top part of the tube and then put it back into place. we've gotten many cars to pass using the same technique! just not too many holes otherwise the emiisions are too low and they might catch on! good luck!

[crzycrkr]

I'll check my EGR ports. How do you check for exhaust leaks? Spray something on and see if it bubbles? Passing smog isn't a problem now, but I still want to make sure that I am not running lean. What sensors control this and which ones should I check?Thanks