need (elec.) diagnostic help - in CO and my car isn't always starting

[davidpertuz@mindspring.com]

Howdy,

I could shore use a bit of help from those
of you out there whoare better at electrical
diagnostics than I am, which should be a whole
bunch of you since I don't have a lot of
confidence in electircs and sort of suck at it
 as a consequence.

This time it's not my garage queen, but my
everyday car, which let me down for the very
first time in 10 years an 190,000 miles.

History: drove from MN to WY SUnday before
last, stopped to get gas, car wouldn't restart.
 No prior problem indicators of any kind. Car
started with jump start. Proceeded to destination,
 parked car. Next afternoon, drove to new site,
shut car off, dead again - no start. Let car sit
overnight, starts fine the next morning, gets me
to the trailhead, worry about car in a week after
backpacking. This Sunday, drive from BUffalo, WY
to Nederland, CO. Get gas in Casper, car restarts
fine. Get gas in Boulder, car stone dead. 10
minutes of chariging from another cra won't
jump-start it. Let it sit overnight, fires right
up the next day. Drive 30 miles to Ned, dead
again. Sit overnight, starts again. You see the
pattern.

These symptoms would seem to indicate an
alternator that is starting to go bad, and not
charging fully. Or a battery that won't hold
charge. Or a bad ground, perhaps.

However.....got battery and charging system
checked with scan tool at a garage in WYoming
- battery, alternator and diodes checked out
fine. Car was starting at that time.

Obtained multimeter for testing.....

When car is dead and won't start, battery
voltage is a normal ~12.6V, a few tenths
lower with accessories on. SO, apparently
full voltage, but won't start. FOr reference,
 checked BIL's truck and has same voltage and
 starts fine, if a little weakly. CHeck car
this morning, fires right up, battery voltage
when off is the same (a few tenths lower,
actually) and a normal 14.4V when running.

When car won't start, still plenty of power
for lights, radio, etc.

Bought new battery (my other car needs one
anyway) and my existing battery (about a year
old)checks out identical to new one - so with
that and the dV found it seems there is nothign
 wrong there.

Alternator checked out OK at garage with scan
tool. Voltage from alt. terminal to battery
ground is same as across battery terminals

Termninals are clean and tight

no dV between battery ground and engine ground -
doesn't seem to be a bad ground anywhere.

The request for help:

Can anyone help me out here with what may be
causing this? Behavior seems in almost all
ways to be that of bad battery or failing
alternator, yet battery is good and alt.
checks out fine according to shop's scan tool,
 and when the car won't start the battery
still has full voltage.

Could the starter be involved, it is a  bit
tought for me to check, since I don't have
anything (jack, but no stands) to support the
car on to crawl under it.

ANy help any of you guys who are good at
electrical and have more diagnostic experience
would be hugely experience would be hugely
appreicated. I need to take care of this this
week before I drive back home to Michigan, and
before this weekend when I will be busy with my
sister's wedding.

Email is the easiest way to reach me, or you
can call me on my cell at 313 623 7627, but it
doesn't work in the mountains where I am - I
have to go to Boulder. You can leave a message,
though. Or, today and Werdnesday you can try me
at my sister's house at 303 258 7121, where I
will be intermittently reachable

Thanks!

David