Hi Jim,
I sincerely appreciate you taking the time to do the writeup below - but my
limited knowledge of electrical stuff makes most of it meaningless.
Did my test of the resistance of the wiring & GPs do any good at all?
Should I ty to get Mercedes to fork over a new relay? If I tell them I
believe it's bad because the resistance of the rest of the GP circuit says
*that* part was good leaving the relay as the only part left as suspect -
would they buy that? I know you cannot speak for the parts guys - just
looking for some way to gauge my possible success ;-)
I hate to keep bothering you about this -- but I'd like to have it working
properly since my wife drives this one all the time. She has no trouble
counting to 10-15 before cranking though. ;-)
I still have the old relay - and it's got a card filled with soldered joints
holding lots of little things in line. If I test those for continuity will
that help point to the part that's possibly bad - or has a bad solder joint?
I may re-install the old relay to see how things act.
OK - back to the new relay and new GPs - it seems like either #1 is bad or
the relay is bad - sound reasonable?
Thanks again for all your time spent explaining this stuff to me - I'm not
dumb, (it only seems that way) but my experience has been mechanical with
electrical limited to getting lights working for the most part --
Larry T (67 MGB, 74 911, 78 240D, 91 300D)
www.youroil.net for Oil Analysis and Weber Parts
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.
----- Original Message -----
From: "Jim Cathey" <[EMAIL PROTECTED]>
To: "Mercedes Discussion List" <mercedes@okiebenz.com>
Sent: Friday, November 03, 2006 12:57 AM
Subject: Re: [MBZ] GP Infant Mortality
got a reading of .4 on all 5 -
The nominal 0.6 ohm (cold, but not too cold) value of the new-style
plugs is in the borderline area of being able to use a garden-variety
ohmmeter to diagnose. Consider the lowly series plug of yore, that
has a nominal (hot) resistance of 0.02 ohms, probably half that when
cold. That's why you use a voltmeter in-circuit to diagnose those,
there's hardly an ohmmeter alive that can give you that number
meaningfully. But fed 50A of current and the nominal 1V dropped
across it is well within the good range of a standard voltmeter.
In effect you're using the remainder of that GP system as a
dummy load for the DUT. No such luck on the parallel system,
you need a hefty series (or clamp-on) DC ammeter to diagnose
those, if the ohmmeter doesn't cut it.
Another idea would be to keep around an old series GP for use
as a shunt for measuring heavy current. It would drop 1-2V feeding
a new-style GP. A little bit of calibration work with a known good
plug or two and you'd have a cheap (and small) test harness for
GP's. Just don't burn yourself!
-- Jim
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