86 Maxima, failing NOx. Here’s what was done. What next?

Not for 10 miles, but for 20+ minutes city/idle.
My concern is that in order to get the cat hotter (highway driving), I
would have to get engine even hotter still,
thus increasing NOx...

wrote:
>
> Sorry, I am not following: if less exhaust gas gets recircuilated back
> into the cylinder, that would cause
> HC to increase? I though it would burn better!?

Well, he explained. Not all cylinders would be getting the same mixture.
Most of the sensors that are controlling fuel mixture are responding to
what's happening to all of the cylinders which are supposed to be all
getting the same amount of exhaust recirculated.

But EGR is the place to look since the whole purpose of having EGR in
the first place was to reduce NOX emissions. As far as I know the
catalytic converter is not helpful in reducing NOX and may even add to
it. Nitrous oxide is not really a product of combustion its just what
happens to some of the nitrogen in the air when exposed to very high
temperatures. EGR makes the fuel burn slower (like an octane boost)
which means the nitrogen doesn't get quite as hot.

-jim

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wrote:

> Not for 10 miles, but for 20+ minutes city/idle.
> My concern is that in order to get the cat hotter (highway driving), I
> would have to get engine even hotter still,
> thus increasing NOx...

Again put premium fuel in and the NOX will drop a BUNCH. You're probably
having inaudible detonation which makes the NOX go up. Retarding the spark
has the same effect if the engione has a timing adjustment, which these do.
Or you can go buy a bunch of parts chasing this if you want to..
--

Steve

http://www.atlantaracing.com

wrote:

> Are you thinking this will retard the timing enough to reduce NOx
> sufficiently?

It doesn't retard the spark, it reduced detonation which is a major cause of
NOX.

> I might as well dump a bottle or two of octane booster instead, no?

No, that won't do it and could likely cause other problems. You need to run
that tank out and fill up with 93 or retard the spark 5 degrees or so and
then retest. I bet light dotonation is causing this problem for you

--

Steve

Thanks Steve, I hope you're right!

jim wrote:
> Well, he explained.

I don't think you got it either. Obstructed passages to some cylinders
would reduce
the amount of recircuilated exhaust to them, and the fuel would burn
better, with less
HC, and hotter. NOx would go up, HC down.

> As far as I know the
> catalytic converter is not helpful in reducing NOX and may even add to
> it.

Ahm, no.

In article
.com>,
wrote:

> jim wrote:
> > Well, he explained.
>
> I don't think you got it either. Obstructed passages to some cylinders
> would reduce
> the amount of recircuilated exhaust to them, and the fuel would burn
> better, with less
> HC, and hotter. NOx would go up,

Consistent with the test report.

> HC down.

Except on the cylinder[s] that are receiving [too much]EGR, those
cylinder[s] will show an increase in HC, consistent with the test
report.

It's a known pattern failure on many Asian automobiles that use
small EGR passages to individual intake runners.
Is it a problem on -your- vehicle, hell, I don't know, like I
said, it's been a while.

> > As far as I know the
> > catalytic converter is not helpful in reducing NOX and may even add to
> > it.
>
> Ahm, no.

Your 86 Maxima uses a three way convertor, so yes, it reduces
NOx, but I wouldn't condemn the cat until I did some more
testing...

>Your 86 Maxima uses a three way convertor, so yes, it reduces
>NOx, but I wouldn't condemn the cat until I did some more
>testing...

Thanks Neil. I get it now.
Based on Haynes manual, the diagram shows one large passage from EGR to

the intake. I have not figured out how to remove the EGR valave assmbly
yet though
to doulbe check -- the manual simply says "remove", so I must be
missing something.
I may swing by the dealership (I need to pick up some minor parts) and
look at the
print out diagram and then do the disassembly.
Thanks for the tip!

wrote:

> The current plan is to put a can of Techron into a tank of 94 gas, run
> it till less then 3/4 left, then
> go take the test again (total cost $10)
> If that fails -- spend $120 on a new cat and pay $30 for another
> emission test.
> Thanks for your advise.

To be sure you might retard the spark 5 degrees or so.

If nothing else fill up AGAIN before the test so you aren't blowing techron
concentrate into the test machine! :-)

--
www.atlantaracing.com

wrote:

>>Your 86 Maxima uses a three way convertor, so yes, it reduces
>>NOx, but I wouldn't condemn the cat until I did some more
>>testing...
>
> Thanks Neil. I get it now.
> Based on Haynes manual, the diagram shows one large passage from EGR to
>
> the intake.

Pull vac on the EGR, if you get a strong responce at idle, it's working well
enough to not be the problem.

-
www.atlantaracing.com