Starting Problems (electric and rather interesting)

[rdh@sli.com (Robert D. Houk)]

   I hope you had a good Christmas Break. Unfortunately I had to spent it without
   my Audi. It was in the mechanic. Here is my story:
   ...
   So far we know, it's not the fusebox, nor the ignition switch. 
   Are there any other suggestions from the net ? Anything I could check
   or have him check ?

Well, I'd start at one end of the wiring harness and work my way to the
other end, suspecting every connector (crimped or otherwise) along the
way . . .

If you're sure it's just the fuel pump not getting voltage, and you have
confirmed this at the fuse, just work your way back from there to the
ignition switch... (easier said than done!)

Your car [well, mine would, can't say fer sur 'bout yours] will happily
crank even if *NO* ignition voltage is present (separate circuit).

In particular, the original Hitachi engine computer for the early UrQs
is allegedly notoriously sensitive to poor voltage. When I first acquired
my UrQ, it had this mode where it would sometimes [usually] start with-
out hesitation, but would occasionally refuse to start at all, wouldn't
even "almost catch", just cranked and laughed at me. I could jump it
from another car with the interesting observation that if the other car
was off (i.e., 12.6V), mine wouldn't not start at all, just cranked hap-
pily away. if the other car was running (13.8V), my car would start im-
mediately! After ripping out the "car alarm", and re-soldering all the
fucked cut'n'crimped connections, my car has started fine everytime
thereafter (going on 2 years now), except when it was below 10F, at which
point it went "graunch" once and then wouldn't even turn over. [I'm 
HOPING my new Diehard will cure that tendency this winter!]

As I recall the UrQ's wiring, the ignition switch +12 goes to the fuse
box which then fans it out to, among other things, the engine computer.
The "starter" circuit is a completely separate switched output that, so
like I said, it can crank all day with no voltage to the ignition and
computer (and fuel pump relay) circuitry.

If the problem's intermittent, you're really hosed! All you can do is
either rewire everything and pray that fixes the problem, or track it
to some point, it starts working, and then eventually fails again and
you can track it a bit further, repeat... Careful examination of the
schematic, coupled with thinking about what powers what, can usually
lead you to "it can only be one of three things" that can account for
the particular set of symptoms you see (e.g., power to computer but
not fuel pump, vice versa, or whatever). Careful "instrumenting" of the
circuit (buy a coupla $10 Radio Shit voltmeters and just leave them
hooked into test points until you see positive failure or not - even
a "negative result" is positive *information*) should tell you which
direction you have to go next. And, like I say, it can be an iterative
process, which can quickly make it prohibitively expensive to have a
mechanic do it - labor costs will kill you. On the other hand, a good
experienced "mechanic" can often times say "Oh, an '83 UrQ with that
damned Hitachi computer, yeah, it's bad voltage to the computer" (which
you'd think a "factory-trained dealer" would be able to do, but in my
experience that is *NOT* the case, they're mostly bozos who know how
to change oil, and maybe exchange computer units) and be right 9 times
out of 10.

At some point, you may well be facing the liklihood of it just being
easier to replace a few things (relay, connectors, etc.) than to spend
10-times-more effort ascertaining that it's the $2 connector and not
the $20 relay . . . (I justify such "blind" replacement policy on the
grounds that, being Audi, whichever is currently working will even-
tually fail anyways, so the replacement is justified as a preemptive
strike!, er, preventative maintenance, yeah, that's it.)

As a general rule - suspect all grounds! (Even if not currently a pro-
blem, refurbing the ground connections -- e.g., cleaning interior con-
nectors, replacing engine-compartment connectors -- is probably a good
idea - flaky grounds are a *real* pain to track down!)

As you meander through the wiring, if any connectors come loose easily,
tighten them! And don't confuse the connector housings firmly mating
with the connectors themselves -- the plastic bodies can firmly lock
up, with the corroded/dirty/loosely-fitting electrical connectors being
a poor/intermittent/non-existent contact! You might even find one "pin"
of a plug/socket is loose! Again, a real bear of a timesink to track
down (but cheap to fix - just push the loose pin back into the socket
'till it "latches", then remate the plug and socket making sure the
"pin" didn't get pushed back out of its plastic housing again. Tug on
each wire of a connector - if it comes out, you've found *a* problem.
Not necessarily the one you were looking for, but you've very likely
avoided a flat-bedding at some future date.

As far as I know, there ain't no better way than just rolling up your
sleeves, and jumping into the middle of the mess, cursing the lineage
of all German electrical engineers as you go along. Try to avoid having
hammers handy, as they tend to wreak more damage than good . . . A sense
of humor helps . . . (Personally, mine was exhausted long ago! But, at
least for the moment, my UrQ is running pretty well)

I wish you the best of luck.

					-RDH