Date: Thu, 21 Jun 2007 03:00:39 -0500
Reply-To: Matt Roberds <mattroberds@COX.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Matt Roberds <mattroberds@COX.NET>
Subject: Re: rough running
In-Reply-To: <20070621031333.QGBM3928.eastrmmtai114.cox.net@eastrmimpi03.cox.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
> From: Pat Little <redtail@CABLESPEED.COM>
> Date: Wed, 20 Jun 2007 16:54:33 -0700
>
> I'm trying to figure out if a slight roughness in my 2.1 is normal and,
> if not, what might be causing it.
The first things to check are the simple ones: spark plugs clean and
gapped correctly; spark plug wires connected and routed correctly, not
chafing on anything; no leaks in the air intake; no flaky connections.
For this last, you might have an accomplice hold the throttle to give
about 1500 rpm, then poke and wiggle all of the wiring you can get to in
the engine compartment. If you can make it happen when you wiggle a
certain wire, check that wire out carefully.
If all that stuff is OK, I don't _know_, but it _sounds_ like maybe
there's a bad spot in the variable resistor that the air flap is
connected to. If you've ever had an old stereo or radio that made
"scratchy" noises through the speakers when the volume control was
adjusted, it's the same thing.
The diagnostic would be to get an ANALOG voltmeter (or if you're loaded,
an oscilloscope) and measure the resistance or output voltage of the
variable resistor that's connected to the air flap (engine shut off).
Carefully push the flap through its travel with your fingers and watch
the meter. If it's a nice smooth steady movement of the needle, then
the resistor is probably OK, but if you reach a "bad spot" in the travel
that makes the needle jump around, that may be the problem.
The quickie fix is to (engine shut off) use your fingers to smoothly
move the flap through its entire travel several times. Don't slam it
into the stops at each end and don't flip it back and forth like mad;
just a nice smooth motion. Do it a dozen or two times, then reassemble
and try the engine again. If this improves the symptoms a little, then
further cleaning of the variable resistor (see below) might help. If
it's still the same, you may need to look elsewhere for the problem.
If you can convince yourself that this is indeed the problem, you *MIGHT*
be able to fix it for a while by applying electronic contact/control
cleaner to the variable resistor. DO NOT USE WD-40! DO NOT USE BRAKE
PARTS CLEANER! These solvents will make it worse. You need something
that is specifically made for switch contacts and variable resistors.
Electronics distributors and maybe even Radio Shack will have the right
stuff in a spray can. Follow the directions on the can, but generally
you apply the cleaner to the control, then operate the control several
times, then let the cleaner dry.
Again, I don't _know_, but the above would be one of my early _guesses_
on the subject.
Matt Roberds
