Date:         Fri, 4 Apr 2003 10:56:51 -0800
Reply-To:     laurasdog@WEIRDSTUFFWEMAKE.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Steve Delanty <laurasdog@WEIRDSTUFFWEMAKE.COM>
Subject:      Re: Voltage between engine and body
Content-Type: text/plain; charset="us-ascii"; format=flowed

Thanks Shawn,

60mV is quite a bit less than I got.
I had 250mV.
Another list member had 330mV...

Next question...
Do you have the noise suppression capacitor on the
back of your alternator, from positive output to ground?


I guess I'll go ahead and explain what I found last
night on mine...

In my quest to troubleshoot the "stalling vanagon syndrome"
I've done some more electrical checking. Didn't find much
unusual *except* :

With the headlight highbeams on and engine running, a DC voltage
measurement taken from the engine block to the body
of the vehicle shows about 250mV. In addition, oscilloscope
measurement reveals that the alternator 3-phase ripple noise
voltage is superimposed on the DC voltage, giving peak voltage
difference of over 580mV between the engine block
and vehicle ground.
WOW! Over 1/2 a volt of noise across the ground from engine
to chassis seems like a LOT to me.

I wonder how the ECU likes that?

Since the voltage drop and noise gets worse with increasing
electrical load, and my stalling problem may also coincide
with electrical loads being on, I'm wondering if this ground
voltage discrepancy isn't a problem.

I have inspected, meticulously cleaned and tightened both
of the ground braids (left head to body and tranny nose to frame)
and they appear to be in excellent condition, and yet they are
obviously... inadequate. For some reason...

So, I added another ground wire, #2AWG from a stud on the
back of the alternator to a clean grounded point in the engine
compartment, away form the stock ground braid.

I also noticed I didn't have the suppression capacitor on the
back of the alternator (from the pos terminal to ground) so I
added one of those as well.

Results:
Now, under the same measurement conditions as before, the
DC voltage from engine to chassis is less than 25mV... less
than 1/10th of what it was before. The peak voltage (DC + AC
noise) is reduced from over 580mV to less than 45mV.

Today I've driven around on various errands, and the bus feels
different.  A very subtle, *almost* not noticeable hesitation or
"surging" at light throttle freeway cruise which was always
there is now quite noticeably absent. Low RPM, part throttle
stop light to stop light acceleration is also noticeably smoother.

It's way too soon to tell if the "vanagon syndrome" has been
affected (hopefully eliminated!) but adding the additional ground
and noise suppression capacitor on the alternator has very
definitely changed something for the better.

Time will tell if the vanagon syndrome is fixed, but I feel
strangely hopeful about this....

It's a cheap thing to add a fat ground wire from alternator
to body, and make sure that the alternator noise suppression
capacitor is installed.  It might be a worthy thing to check
into for folks suffering from "the syndrome".

Steve



At 08:51 AM 4/4/2003, you wrote:
>Someone asked about voltage between engine and
>body with engine running, so here are the results using a
>digital VM:
>
>'88 Westy with stock 2.1L with intermittent hesitation
>sydrome.
>
>Engine dead cold. (2 deg C)
>Started, turned on highbeams
>Opened engine lid, tried to find rust free bare metal or
>bolt on body. Gave up and used exhaust heat shield for
>body connection.
>Tried various engine block areas, and got same
>readings at idle, so finally jammed probe into gap near
>bellhousing.
>
>Readings were a solid 0.06V at idle, changing to a
>steady 0.056V at approx 2000rpm.
>
>Is this the surprising data you were expecting?
>
>
>-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
>Shawn Wright, Systems Manager
>Shawnigan Lake School
>http://www.sls.bc.ca
>swright@sls.bc.ca