Date:         Thu, 31 May 2007 15:51:35 -0500
Reply-To:     Matt Roberds <mattroberds@COX.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Matt Roberds <mattroberds@COX.NET>
Subject:      Re: Backfiring. How to proceed?
Comments: cc: vanagonvw <vanagonvw@GMAIL.COM>
In-Reply-To:  <20070531173209.WOQJ17069.fed1rmmtai109.cox.net@fed1rmimpi01.cox.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed

> From:    vanagonvw <vanagonvw@GMAIL.COM>
> Date:    Thu, 31 May 2007 11:05:09 -0600
>
> I have been told that backfiring is almost always a hole in the exhaust
> so that is where I am looking.

It can be, and it's simple to check.  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.  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.

> FWIW, it does pretty well kill the engine if I block off the tailpipe
> while its running. That is how they test for leaks during an emissions
> test. Not very reliable, but I did it anyway.

IMHO this is actually a pretty good test, if you can kill the engine
totally by using a wet rag on the tailpipe.  If it is leaking a little,
you will usually hear the leak get louder before the engine stalls - it
may help to have your head under the engine and/or free to move around
while somebody else blocks off the tailpipe.

> If I had done anything to the engine settings, I could see that maybe
> it has leaned out or something, but nothing has been touched in that
> area for years.

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.  :)

Matt Roberds