Date: Tue, 21 Aug 2012 20:46:13 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Mark D? Someone with a scope?
In-Reply-To: <50341e80.5291cc0a.4545.ffff80e1@mx.google.com>
Content-Type: text/plain; charset="US-ASCII"
The idle speed stabilizer shares some of the ECU inputs such as temp 2 and
of course the tach signal. This along with the pulsing of the idle valve
puts noise on some of the circuits. With two devices sharing the temp 2
circuit a good ground path is really critical. Un plug the idle controller
and watch some of those readings change.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
David Beierl
Sent: Tuesday, August 21, 2012 7:49 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Mark D? Someone with a scope?
Hi Volks,
I wonder if someone out there has a scope and can look at the hash on the B+
and maybe a sender lead like T-II or AFM?
I've been looking for example at the AFM lead, referenced to the ground bolt
by the ECU (2.1l) and it's sitting at a pretty constant
~2 volts with the engine idling. But on that two volts is riding a bunch of
junk that I have to verify by examining B+, but I'm pretty sure is switching
hash from the alternator regulator. There's some regular squarish-wave
oscillation that comes and goes at a few hundred mV (and on the T-II signal,
for example, where the base signal is something like 0.1 V when the engine's
hot, the oscillation makes it average a couple tenths higher); but the most
striking thing I'm seeing is a regularly repeating pattern with more than
1.6 millisecs before a repeat. It starts out with an underdamped wave at
4 mHz with p-p amplitude of EIGHT VOLTS for the first cycle or two, then
after that dies away the voltage gradually droops and then descends in a
smooth curve with minimum about -2 V, the same as the bottom of the first
cycle of the big spike. There's some low-amplitude (1-2 V) oscillation then
the voltage gradually climbs back up to the average value. Total time is
about 8 microsecs.
I'm not very happy seeing all that junk on B+, but it really bothers me that
it's leaking through the ECU into the sender inputs. My greatest concern is
actually T-II, where as I said the average value of the signal rises a
couple tenths of a volt when you start the engine, making it getting on for
three times as high as it should be. I'm pretty sure my 1.9l didn't do
that, as I had a Digitool hooked to it for quite a long time.
Can anyone compare this with their own beast and give me a heads-up?
A year or so ago I was looking at what's on the alternator B+. I'll have to
revisit that but whatever I was looking at I tried adding a bigger capacitor
on the output and it started ringing like crazy. I didn't have a big choke
to try.
Thanks,
David