Date: Thu, 7 Feb 2008 21:07:08 -0500
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: SMOG TEST failure
In-Reply-To: <47AB86A5.807@ucsb.edu>
Content-Type: text/plain; charset="iso-8859-1"
Emissions issues really are straight forward for those who know how the
system works, what should happen normally, and what causes the various gas
failures. Results like you are the justification for emissions test
procedures and with your numbers you are definitely in the league of a
gross polluter.
For starters, in order for anyone to diagnose you problem, you also need
to state the CO amount. For diagnosing, you really want to measure the CO
before the catalyst. That is why there is a test port.
I'll go over the gasses again and if someone wants, feel free to post this
on the Wiki.
Carbon Monoxide is the result of incomplete combustion due to insufficient
oxygen being available or combining with the fuel to complete the burn.
Yes, this is the one that is mixture, and temperature related. Why
temperature? The big un-vaporized fuel molecules may not get the oxygen
even if it is available. That is why there are winter fuel blends and we
need enrichment to get cold engines started. If the CO is in limits, the
fuel injection is basically working. The Vanagon should be able to get
near 1% even before the Cat.
Excessive Hydrocarbons. This is fuel that never started to burn or get
ignited. Yep, raw gas out the pipe. Usual causes are ignition miss fire,
leaking valves, rings, etc. Another phenomenon here is what is known as
the "Lean" miss fire. This is due to slight differences in mixture amongst
cylinders with the leaner one failing to "light up". This is that crazy
intermittent miss that can drive you crazy. The Vanagon engne is really
prone to this due to the poorly designed intake system. Over advanced
ignition timing will also add to this as the advance timing will require
much less air and fuel to maintain a low idle speed. This results in poor
swirl and mixing and the fuel mix will fail to light. If an oil change
fixes this, consider you have a ring or valve-guide problem. Excessively
lean or rich mixtures will result in the miss fire.
Oxides of Nitrogen (NOx). This is the result of excessive flame
temperatures. Engine design, ignition timing, and load all add to create
this. The controls are timing settings (why we have the dual diaphragm
distributors before Digifant), low compression, most vehicles EGR, and in
everything 81 and later the three way oxidation reduction catalyst with
the O2 sensor for final mixture control. The downside of this is that we
can no longer use lean mixtures to improve fuel economy. This is also a
major problem with Diesel engines as they have high compression, and lots
of excess air.
Now give us the rest of the readings and I will try to give you diagnoses
and direction. Resist the temptation to tamper with the afm and make blind
adjustments or start changing parts.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
John Goubeaux
Sent: Thursday, February 07, 2008 5:31 PM
To: vanagon@GERRY.VANAGON.COM
Subject: SMOG TEST failure
My 90 failed the California smog test today. In short, the idle values
were off with HC ppm at 424 where max allowed is 120 though the 2500rpm
values passed fine and are way below limits.
So I am looking for some clues on where to start with this, and while I
realize it might not be straight fwd, thought I would see if anyone has
some insights. Replacing components one by one might get expensive so i
was hoping on narrowing it down on what it **could be.
Idle is fine though it has been rough for a while at startup and I have
had intermittent, what appears like missing at high speeds when
accelerating. I had thought that i was seeing what folks refer to as
the "vanagon syndrome" but with with the idle values like these am
thinking that it could be as a result of the idle control valve (though
it vibrates), the idle control unit or the coolant temp sensor (which i
am told can cause a rich mixture.
It looks like Bentley has clear steps to trbl shoot the idle though I am
not sure, without the proper tools, if I can make the needed adjustments
it calls for.
Thanks in advance for any wisdom that can be shared..!!
-john