Date:         Thu, 31 May 2007 16:11:35 -0600
Reply-To:     vanagonvw <vanagonvw@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         vanagonvw <vanagonvw@GMAIL.COM>
Subject:      Re: Backfiring. How to proceed?
Comments: To: Matt Roberds <mattroberds@COX.NET>
In-Reply-To:  <Pine.LNX.4.64.0705311542020.12036@birdbird.example.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

>   Another cause is an engine running
> lean - look over your air filter housing, any gaskets or rubber boots
> between the air-flow meter and the heads, etc.
Been over it, but intend to do it again, because I am sure wanting it to
be something simple :)

> Is your state test just
> a visual inspection or do they put a sniffer on it?  If they sniff it,
> the numbers from that test may be useful.
at 15mph:
HC  ppm 122  vs max allowed of 398
CO % 1.04  vs max allowed of 3.08
NO ppm is 1848 vs max allowed of 2723

at 25mph:
HC  ppm 125  vs max allowed of 343
CO % 0.86  vs max allowed of 2.98
NO ppm is 1696 vs max allowed of 2523

They also measure % of CO2 and its 14.4, and %O2 = 0.6  pretty much
identical at both RPMs

I think they are amazing numbers, for no cat, and no EGR system....but
perhaps the indicate something I don't understand?

>
> IMHO this is actually a pretty good test, if you can kill the engine
> totally by using a wet rag on the tailpipe.
Everyone says its okay, so I am becoming convinced. Just sounds like a
brutal thing to do to an old engine... :-)

I am thinking that while I do a leak down test, I could also block the
tailpipe, and do each cylinder with the exhaust valve open. That ought
to give me a quieter, safer way to see if I have issues on the exhaust
side.....

>
> If you can't find anything obviously wrong, like a cracked hose or bad
> gasket, it might be a good time for a full tune-up.  Twiddling every
> adjustment there is every 5 miles will make your engine unhappy, but so
> will not touching any of the adjustments for 50,000 miles.  :)
>
Thanks Matt. I appreciate the assist. Unless I miss my guess, there is
precious little to adjust, beyond cap, rotor, and plug replacement. The
test mechanice does the CO adjust each year when it is needed, and I
don't think tweaking the AFM is a good thing, :-) so is there something
else I should be dealing with? Based on how I drive it anymore,  no more
than 3000 miles per year,  when I said years, I meant probably less than
20,000 miles....<g>

John