misc to robert & list

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

	   In a previous post, you mentioned an occasional leaning out 
   problem which you blamed on bad grounding.  What were the specifics of
   the problem, and what did you do to alleviate it?  Was the problem due
   to low voltage to the  fuel pump?

The problem manifested itself as A) erratic stumble at idle; B) the
frequency valve behaving in a very schizoid manner (BZZZZT pause BZT
BZZT pause BZT pause BZZZZZZZZZZZZZZZZZZZZZZZZT pause click pause etc.)
and C) lack of/rough top end -- top end in this case being 5 grand or
so.

Item "A" should not be confused with a random stumble at idle caused
by a small tear/leak in the air tract someplace downwind of the air
sensor flap...

Item "C" was confirmed by monitoring the O2 sensor voltage at full
throttle up a convenient long uphill 8-lane-divided highway, with
voltage dropping to 0 rather than hanging out at +.7V or so.

PEDANTIC MODE ON:

   The full throttle switch is supposed to trigger the computer to switch
   into [minor] over-rich mode driving the frequency valve [what a stupid
   name] to raise the fuel distributor control pressure (or is is lower
   the fuel distributor control *back* pressure? Never can keep all that
   magic plumbing straight in my mind...), which should manifest itself
   as a "high" O2 sensor voltage: +.5V being nominal ideal (aka "stoi-
   chiometric") value, lower voltage indicating lean, higher voltage in-
   dicating rich...

   Sorry if this is too pedantic for some of ya, but this was an exten-
   sive (not to mention expen$ive) learning process for me; so if I can
   get a [very] minor buzz by appearing to know of which I speak, I fi-
   gure I've earned it!  <snort!>

PEDANTIC MODE OFF:

The ground-connection-as-culprit was empirically determined by the me-
chanic (Dave Clark, of the Benz Den in Belmont, MA., very competent,
and yes this is a plug...) taking a poker (I'd call it an ice pick if
it didn't say SnapOn on the handle...) and prodding the mass of ground
connections that come together on the ignition coil mounting bracket.
He went "push" and the computer said "Duh?" and shut the engine off,
and he said "See, bad grounds, solder those suckers" (or words to that
effect). After cutting off all the SFC (Stupid F*****g Crimped) con-
nectors, and soldering on new ones, the engine idled much more consis-
tently (no erratic stumbles), the freq valve happily buzz'ed to itself,
and O2 sensor voltage held .6-.7V to around 6 grand or so.

(While I make it sound all very simple and obvious, this is a condensa-
tion of nearly a full day's poking, proding, testing, head scratching,
swearing, and so forth...)

	   I'm curious because I had a similar problem in my Ur, but it was
   due to power, not ground.  There was a single wire (around 10 gauge or so)
   that was supposed to feed the fuel pump, power windows, and a few other
   high current items.  This wire was CRIMPED to a spade connector with a 
   plastic shroud around it, which in turn plugged into another crimped
   connector of the opposite sex.  Well, what happened over the years was
   the high current demands of the fuel pump and other associated items
   produced a voltage drop across the relatively high resistance of the
   F*****G crimp (this is not to say that there should have been a higher
   gauge wire used in the first place, but I digress...), which heated it up 
   some, which in turn caused the crimped connection to oxidize more, which
   made it even a higher resistance, which heated it up even more, which....
   Well, you can guess the rest - by the time I discovered the problem, the 
   conection had gotten so hot it had burned the plastic shroud!

Ah yes, I know that wire whereof you speak! It is in fact a 12ga (Red/Black,
as I recall?), that is fed by the ignition switch via a 16ga black wire!
The whole circuit I believe goes 10ga unswitched +12 from fuse panel to
ignition switch, 16ga (Black) back into fuse panel switched +12 bus, which
among other things feeds out of the fuse panel via 12ga to the "Y" connector
you mention which feeds the fuel pump relay (from there to fuel pump fuse to
fuel pump) on one leg, the other leg going back again to the fuse panel
where it feeds the #15 fuse/circuit (radiator fan -- 25A).

	   The solution was to run another wire in parallel with the original
   10 gauge and SOLDER it along with the original to the connector.  This has

I "attacked" this from the other direction - I disconnected the "other" leg
at the fuse panel, and routed a dedicated 10ga from the battery to the #15
fuse/circuit connection, offloading the radiator fan from everything else
(in particular, the ignition switch!). [I dunno, maybe this is why Audi
chose to have the A/C drive the radiator fan high speed directly from the
A/C double-relay bypassing the ignition-switch-fed fuse panel bus...] This
left the fuel pump as the sole load on the 12ga wire, and essentially the
sole load on the switched +12 bus in the fuse panel. Just about every-
thing else "switched" is further indirected by the "Acc" +12 bus, which
is controlled by the "load reduction" relay (left-most on main fuse panel,
I think) which is itself switched by the "switched +12" (aka "#15 terminal"
[not to be confused with the #15 fuse/circuit aka radiator fan circuit] in
GermanSpeak). This Acc +12 bus mostly switches other relays, in particular
the AC power relay (which in turn feeds unswitched +12 to the fresh air
fan and other A/C relays [one of which eventually feeds the radiator fan
high speed winding], and the power window/mirror relay (which feeds a 25A
fuse on the aux fuse panel to the window motors, and the 8A fuse also on
the aux fuse panel to the mirror motors/clutch/heating coils). I think the
rear window defogger is directly off the Acc +12 sans relay, but I didn't
really get involved with that piece of wiring. (And, for completeness,
the headlights are (stock wiring) fed by a second tap on the ignition
switch, 12ga yellow wire, which then runs off as a 16ga to feed some other
widgets, like the radio, maybe? This has the effect of switching on the
lights only on the middle position, switching the lights off in START as
well as OFF key positions.)

I think I got all the ()'s and []'s and whatnot correct above; I think it
"does justice" to the Audi wiring/circuitry . . .

   helped my lean-out problem a great deal, but I'll occasionly get a stumble
   at high boost on a cold night.  This is why I wanna know what problems you
   had with ground.  I was thinking of putting a relay under the seat near the
   battery, and using the standard fuel pump voltage to activate the primary
   of the relay - I've heard of others doing this.

Yeah, I thought about that as well; I may yet get motivated to do just
that (although it offends my sensibility to have the computer switch a
relay to switch a relay; in practice however, it is very easy to do, as
the fuel pump wire runs about six inches past the battery just before it
disappears through the floor pan to the fuel pump). A good solid +12 feed
to the fuel pump seems like a VeryGoodThing(tm), right after a good solid
+12V feed to the engine computer itself.

In fact, I have toyed with the idea of installing a DC/DC regulated power
supply solely to drive the engine computer! Yes, that is a hint of des-
paration in my "voice" here... For all that Audi may well be the World's
Best Engineered short block (100,000 miles on the pistons and, except for
the two that had obviously "contacted something", looked brand new), their
electrical competence would shame the average high school dropout. (Al-
though I must also point out that the actual *computer board/box* used in
at least the early UrQs was manufactured by Hitachi...presumably to Audi
specs...I wonder if they actually specified "becomes schizoid at +11.5V",
or if that was simply some Hitachi engineer's idea of a joke??)

I'm still tracking one misbehavior -- at idle with heavy electrical load
(high beams, A/C max (fresh air fan and radiator fan both on max draw),
rear window defogger on: the system voltage wavers at around +12 (with
minimal load it holds pretty solid at +13.7V to +13.9V measured at the
battery), then suddenly collapses to +10-+11 at the same time as the en-
gine rpm suddenly drops to a rough inconsistent 500rpm (from 800-850)
shortly before dying altogether. It looks like the voltage regulator is
deciding to just switch off altogether, triggering the engine computer
to flake out, letting the engine die. (alternatively, the low voltage
might cause erratic/inadequate ignition/spark, which causes the engine
to die...) It appears that the voltage drops just an instant before the
engine speed drops, but it's a sufficiently short interval that it's hard
to call for sure. The main reason I tend to suspect the voltage regula-
tor and/or computer is that if I suddenly switch off the electrical load
(lights and rear defroster), the voltmeter lurches upwards to +14 and
the engine goes DRAMATICPAUSE and either shuts off altogether or recovers
and idles smoothly again. Another potential underlying cause might well
be semi-fouled plugs (weak spark at "merely" +12) since if I goose the
engine when it drops to 500rpm (before it dies altogether), it will again
hold idle for awhile (5-20 seconds) and repeat the whole cycle. Another
observation is that once the voltage has "collapsed", shutting down the
electrical load and reving up the engine only brings the voltage back to
about 13.5, slightly but notably lower than the "14" (13.9) it held just
after initially started. Shutting off and restarting still only yields
13.5, shutting off and coming back an hour later yields 13.9 again.

Of course I can just cheat and up the idle to 1000rpm (just as soon as I
can dislodge the damn frozen idle air adjust screw...), but that's es-
thetically less pleasing.

					-RDH