Date: Thu, 7 Feb 2008 18:28:11 -0800
Reply-To: John Goubeaux <john@UCSB.EDU>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Goubeaux <john@UCSB.EDU>
Organization: University of California Santa Barbara
Subject: Re: SMOG TEST failure
In-Reply-To: <BAY125-DAV2C03DE5DE129FBBE051A8A02F0@phx.gbl>
Content-type: text/plain; charset=iso-8859-1; format=flowed
Thanks Dennis,
Good summary. Here are all the numbers in order to better diagnose:
rpm %CO2 %O2 HC(ppm) CO
% RESULTS
MEAS MEAS MEAS MEAS
______________________________________________________________________
915 11.9 3.2 424
0.55 GROSS POLLUTER
2571 13.9 0.5 66
0.55 PASS
Dennis Haynes wrote:
> 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
>
>
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