87 Sentra emissions test failure

B Trevino · 03-29-2008, 01:43 PM

I have a 1987 Sentra (with Ca emissions) which failed emissions test for high Nox readings. I reached under the egr valve to its diaphragm and confirmed that it does move. (Note: It passed spec at 15 mph test, but failed the 25 mph test). I noticed that the tech manually resticted the auto transmission to using only second gear, instead of letting the trans shift to third on it own. As a result, the engine speed was held higher than in normal operation. The car had been left running for about 20 minutes while waiting for tech to test vehicle in 95 degree ambient temp(F). Since NOX emissions are resultant from high combustion temps, and the readings passed at 15 mph, does it seem likely that readings would have been significantly affected by:
A) ambient temp.
B) shift selection and /or
C) length of time left sitting still prior to test.

I appreciate any help to get this car to pass emission testing. Thank you very much...B

cardoc · 03-29-2008, 03:31 PM

Does it move when it's suppossed to or are you moving it?If you move the valve manually open does it stall the motor at idle indictating that the passages are clear.Over advaced ignition timing or a lean mixture at that rpm will also raise NOX.As would a very hot engine.A,B,C all could effect NOX in theory.
Cardoc

**Snoopdogie187** · 03-29-2008, 03:43 PM

with the egr, it can still move by hand, but can get stuck. what i mean is that you may be able to push it open, but if done just right it wont let it open or close as easy as it should.
i changed an egr on a 92 pathfinder (very easy to do, but part is like 100 or so) and before taken the old one off, if i plyed with it then let the engine run, it would work muh better then if I did not it would give problems.

Anyway, if you are going to push on the diapharm and push on it, do it slowly and make sure it is smoth and goes easily. you will probably know better what I mean when doing it.

**qldit** · 03-29-2008, 06:55 PM

Good Morning Gentlemen might be an idea to see that all the inlet manifolding and vacuum system is perfect also.

Aren't these kinds of problems good fun!

Cheers, qldit.

03-29-2008, 01:43 PM	#1 (permalink)
B Trevino Registered User Join Date: Mar 2008 Posts: 1 OS: xp	87 Sentra emissions test failure I have a 1987 Sentra (with Ca emissions) which failed emissions test for high Nox readings. I reached under the egr valve to its diaphragm and confirmed that it does move. (Note: It passed spec at 15 mph test, but failed the 25 mph test). I noticed that the tech manually resticted the auto transmission to using only second gear, instead of letting the trans shift to third on it own. As a result, the engine speed was held higher than in normal operation. The car had been left running for about 20 minutes while waiting for tech to test vehicle in 95 degree ambient temp(F). Since NOX emissions are resultant from high combustion temps, and the readings passed at 15 mph, does it seem likely that readings would have been significantly affected by: A) ambient temp. B) shift selection and /or C) length of time left sitting still prior to test. I appreciate any help to get this car to pass emission testing. Thank you very much...B

03-29-2008, 03:31 PM	#2 (permalink)
cardoc Registered User Join Date: Apr 2007 Location: Ct. Posts: 189 OS: win xp sp2	Re: 87 Sentra emissions test failure Does it move when it's suppossed to or are you moving it?If you move the valve manually open does it stall the motor at idle indictating that the passages are clear.Over advaced ignition timing or a lean mixture at that rpm will also raise NOX.As would a very hot engine.A,B,C all could effect NOX in theory. Cardoc

03-29-2008, 03:43 PM	#3 (permalink)
Snoopdogie187 Oh! What shall I be? Join Date: Jun 2002 Posts: 2,540 OS: Vista Home Premium SP1, mom: XP Pro SP2 My System	Re: 87 Sentra emissions test failure with the egr, it can still move by hand, but can get stuck. what i mean is that you may be able to push it open, but if done just right it wont let it open or close as easy as it should. i changed an egr on a 92 pathfinder (very easy to do, but part is like 100 or so) and before taken the old one off, if i plyed with it then let the engine run, it would work muh better then if I did not it would give problems. Anyway, if you are going to push on the diapharm and push on it, do it slowly and make sure it is smoth and goes easily. you will probably know better what I mean when doing it. __________________ Infected computer? click here Has TSF Helped You? Posting System Specifications Please Donate to TSF

03-29-2008, 06:55 PM	#4 (permalink)
qldit TSF Gearhead Join Date: Mar 2007 Location: Brisbane Australia. Posts: 592 OS: All Systems, mainly Linux	Re: 87 Sentra emissions test failure Good Morning Gentlemen might be an idea to see that all the inlet manifolding and vacuum system is perfect also. Aren't these kinds of problems good fun! Cheers, qldit.