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autocheck system contains a 'diode pack' to allow one input to
check two conditions.  "Brake system defective" thus has multiple
meanings on such cars.  The manuals are very poor, and J67 (the
diode pack) has eluded us for some time - no location is given for
it.  It's actually mounted on the wiring harness, just where it
splits below the fusebox.  Why couldn't we find it?  There's a bug
in the spare parts diagram - whoever drew it labelled the loom 'o1'
instead of '01', deleting the index entry for the diode pack, which
is '1'.  Computers - don'tcha luv 'em?

Has my fuel pump been jumpered?

Some of the cruder 10V 'chippers' can't reprogram the ECU to raise
the overboost cutout limit, and so they simply hard-wire the fuel
pump so the ECU can't switch it off.  This achieves their
objective, but disables an important safety feature.  It's
especially common on WRs.  Often this has been done by a previous
owner, who has driven the car for a while, then replaced the
original wastegate spring and sold the car to an unsuspecting buyer
as "never been chipped".  You can check for fuel pump jumpering on
a WR by starting the car, detaching the ECU hose from the inlet
manifold, and attaching a bicycle pump to the hose.  With the
engine above 3000 rpm, pump gently until the dashboard boost gauge
shows maximum boost.  At or just above this, the engine should cut
out.  The same technique works on the MB, but an external boost
gauge is required since the MB doesn't have one on the dashboard
display - even though the MAC12D ECU generates the required
signals.

It goes in BACKWARDS!?!

Audi's service documentation states quite explicitly that some
bolts MUST be inserted from the rear of the car with the nut facing
the front.  One prime example is the lower ball joint clamp bolt on
each suspension strut.  The reason is safety - the longtitudinal
G-force experienced during braking is much greater than anything
achieved during acceleration - should the nut ever fall off,
natural use of the car will cause the bolt to slide forward during
braking and remain in place - even without a nut.  Of course, the
nut shouldn't ever fall off - for this reason Audi recommends that
both the self-locking nut and the bolt be replaced each time.
Self-locking nuts should only ever be used once - but the bolt is a
different issue.  Where there is no corrosion (e.g., on the bolts
securing the pedal frame to the car inside the passenger
compartment) then it's OK to replace just the nut.  Where there is
corrosion - nowhere more of a problem than on the suspension - then
the bolt must also be replaced.  Winding a self-locking nut over a
corroded bolt just destroys the self-locking function, regardless
of whether this is achieved with a plastic insert or deliberate nut
malformation.  Of course, as many of us know, corroded bolts have a
self-locking function all of their own.  Don't forget that wishbone
bushes must not be fully tightened until the car's weight is on its
wheels.  If they're tightened with the car in the air and the
wheels unsupported, putting the car back on its wheels applies a
strong bias to the bushes leading to early failure.

Exhaust manifolds revisited

We seem to bang on a lot about 10V exhaust manifolds, but then
that's what they do in many members' cars.  As we've said before,
the primary cause of manifold cracking seems to be failure of the
right engine mount causing the engine to sit on the subframe.  You
can test for this by trying to pass a strip of paper around between
engine and subframe.  The turbo is heavy and supported only by the
manifold - if the mount has failed, road shocks are transmitted
directly to the assembly like hammer blows.  In turn, the principle
cause of engine mount failure seems to be the rusting away of the
heatshield that should protect it from exhaust heat.  The problem
doesn't affect the 20V engine because all the heat is much further
away from the engine mount.  If its environment is correct (good
mount, intact heatshield) there is no evidence that the original
Audi 10V manifold has any undue liability to crack.  Another source
of problems is leakage, primarily caused by loose nuts, and this is
where the story gets interesting.  First of all - a loose stud or
nut is easy to detect on a cold car, because the thick washer
underneath the nut can be turned with the tip of a finger.  But why
do they come loose?  Here's the good bit - the service microfiche,
spare parts microfiche (and the ETKA system now used by dealers)
list a speednut (N 012 608 1) to lock the primary nut in place.  On
many cars, this is missing - even where no known intervention has
taken place.  If you do have the misfortune to have to replace a
10V manifold, specify that the fasteners, engine mount and
heatshield should also be replaced (about GBP110) and that speednuts
should be added - at 40 pence each they're cheap insurance.
Exhaust manifold studs should always be replaced - they're only 70
pence each and a major source of problems when reused.  And if your
manifold isn't cracked, make sure you have the right (offside)
engine mount checked at the next service - it's about three hours'
labour to renew it.

Just one oversize piston?

Conventional wisdom is that an engine with one or more scored bores
must be rebored and fitted with a complete set of oversize pistons
- otherwise the engine would be out of balance.  It seems that this
has changed; in some european countries regulations require that
reboring an engine and fitting oversize pistons doesn't change the
power output.  Accordingly oversize pistons have different gudgeon
pin locations and a different crown.  An hour or two on the phone
to the manufacturer's technical department in Germany seems to
confirm this - oversize pistons may be fitted singly without
disturbing the balance of the engine.  Our scepticism has not yet
been overcome, so one engine is being repaired this way as an
experiment.  More later.

A tip from the USA for MB and RR owners

The screen fitted in the hydraulic fluid reservoir is not 'total
pass' - it has slits that allow oil to bypass the filter and carry
contaminants back into the system.  In fact, the only really
effective screen is in the banjo bolt on the side of the brake
pressure accumulator.  It's therefore a good idea to drop a small
magnet into the reservoir screen.  You can remove the screen
completely by putting your fingers into the top of the reservoir
and working it upwards - when there's enough to grab hold off, pull
it upwards.  It will stop suddenly - just keep pulling.  Wash it
carefully in degreaser or paraffin and then water, dry it and
replace it.

On the subject of RRs and bombs ...

In recent months we've seen no fewer than four cases of brake
pressure accumulator ('bomb') failure in 20Vs.  It's entirely
possible that a slightly substandard batch was fitted at the
factory.  Testing the bomb is easy - attach an ohmmeter or test
light to the pressure switch mounted diagonally on the brake servo,
run the engine for thirty seconds, switch it off and start pressing
the brake pedal.  The absolute minimum of depressions before the
switch closes is three.  This test should be performed at least
once a year - perhaps at the annual service.  On the 20V the supply
hose uses two plastic sealing rings (N 904 054 01) and these should
always be replaced with the accumulator.

Has your zerk been zapped?

This is another annual job.  Zerk is US slang for a grease nipple,
and your ur-quatro has one on the propshaft universal joint - the
repair microfiche says it should be greased every 30,000kms, but
the maintenance instructions to dealers don't mention it so it
never gets done.  One joint recently took 17 squeezes of the grease
gun lever.

A Quick Safety Check

Following a freak incident in Canada - no damage or injury - can we
suggest that any quattro owner with cruise control of the
rod-actuated type fitted please check that the retaining clip on
the end of the rod that attaches to the throttle quadrant is
properly in place?  This does not apply to cars without cruise
control or to cars with cable-operated cruise controls.

The Hawg Ring Lunge

Many ur-quattros that we see have collapsed side bolsters in the
driver's seat (look for foam crumbs underneath) and/or failed seat
heaters.  It seems appropriate to discuss repairing these at this
time of year - it's a job you can do inside the house, a firm right
bolster is worth 10 mph in a left-hand bend, and a nice warm bum is
lovely on a cold morning.

The seats are very easy to remove - a 5mm Allen screw and a 10mm
nut secure the front of the slider and two screws secure plastic
bits at the rear of the runners.  Line the rear footwell with
newspaper so you don't get grease on the carpet.  Don't forget to
unplug the heater cable and, on a WR, the driver's side seatbelt
warning switch.  Finds under the front carpet invariably include a
boiled sweet (factory fitted?) and a couple of pounds in small
coins.  More unusual finds have included an unopened pack of gum,
toilet requisites and live ammunition.

Once back in the warm and dry, check the plastic side panels in
good light.  Each side is secured by three little dowels pushed
into expanding clips.  When these dowels are removed, the panels
just pull off.  Make a careful note of the wire locations in the
heater plug, and undo it to release the wires.  Remove the rake
adjustment knob - it's held on by three tongues and you can reach
inside the back of it with a hook and pull them off one by one.
Don't worry - a new knob is only GBP3. Once it's off, remove the
adjustment mechanism.  The back is held to the base by two clevis
pin type fittings with push-in clips - just pull them off and
stretch the arms out over the pins.  The seat should now be in two
pieces.

To remove the lower cover, you will have to remove the two bushes
onto which the catch engages when the seat is locked in its normal
position.  If these bushes (part 171 881 299C) are worn, replacing
them can cure a lot of seat rattle for very little money - about GBP1
a seat.  Code 01Z is dark brown, code 01C is satin black.  If the
seat base is loose in the runners, new guide pieces are about the
same price.

If the seatback squeaks loudly when wiggled from side to side, the
usual cause is a fatigue crack in one or both top corners of the
seatback frame and this will have to be welded.  Get the welder to
insert a supporting fillet - Recaro's design is not the best.
Didn't you know the stock seats are Recaro?  Check out the stickers
on the seatback frame.  The rear seat cover comes off fairly easily
- the headrest has to be removed to get its plastic fixings out of
the seatback.  While the seatback is dismantled, check the cable
that operates the catch - it frays at the nylon runner halfway down
the back.  If you need a new cable, take care to get the correct
one - there are six different part numbers based on your VIN
number, and even then they're not always correct.  It's a good idea
to go to the dealer armed with the length of the old cable in
millimetres - valid numbers are 342, 363, 370, 580, 689 and 765.
Running repairs can be made with bicycle brake cable fixed with
double screw blocks cut out of domestic 15 amp terminal blocks.

If you're repairing the heater, check the backrest and base for
continuity.  The elements are wired in series, and a break in
either will stop both from working.  Some people have successfully
repaired breaks by soldering, but it's tricky as the elements are a
silver alloy and ordinary solder doesn't work very well.

Remove the seat cover you're interested in.  This will usually be
the base.  You'll need good side cutters to cut the hog rings that
secure the cover to the steel wires passed through the cushions.
More of this later.  Count the rings you cut and clear out all the
fragments.

The replacement element (443 963 555S, GBP98 + VAT) goes inside the
seat cover.  Don't be tempted just to lay it on the seat cushion
underneath the cover - it will then be underneath the foam in the
seat cover and will hardly warm your bum at all.

Lay the cover out, surface facing down and lay the replacement
element on top to get the orientation.  Note that the wires should
come towards you - not towards the seat cover surface.  Otherwise
you'll feel the lump when sitting on the seat.  You can see that
you'll have to cut two slits with a very sharp knife in the cloth
backing of the seat cover to thread each arm of the element through
- it comes out the other end and the tab is folded over.

You actually cut through the cloth backing and the thin foam layer
- the element slides in right behind the old element, which stays
in place. Don't even think about removing it.  A ruler is ideal for
pushing the new element through.  Cut the slits with the knife held
over at 45 degrees - otherwise you'll get a small ridge in the seat
when reassembled.  Use a knife with disposable blades - it will be
blunt before you're done.

When you replace the seat element (as opposed to the backrest
element) you still need the sensor in the old element.  Trim off
the (now unused) supply wires to the old seat base element, but be
careful to leave the sensor wires intact.

You need two tools for stretching the seat cover back on using the
proper hog rings.  Don't be tempted to use cable ties - they're not
designed to take intermittent loads and often give way after a year
or two.

a) The Hook.  This is made from a wire coathanger.  Take a
straightened piece and form the smallest hook you can in one end.
Make a handle at the other.  Don't throw this away after doing the
job - it's ideal for replacing the spring clips on the air filter
box and retrieving the hydraulic pump belt when you've dropped it
down the front of the car.

b) The Pliers.  We use Mark-Line 12108 - Snap-On YA808 is an
alternative.

You also need a pack of hog rings - Audi's cheapest spare part. N
015 261 1 is around GBP10 for a pack of 100 - you need 26 for a
complete seat.  If you have any problems getting the pliers or the
rings, try a specialist upholstery factor.

Put the cushion on the frame, and start stretching the cover over
it. A new base cushion from Audi is about GBP70. Remember where you
cut off the old hog rings?  As a check, you should put back the
same number you cut out earlier.  The replacement procedure is to
load a ring into the pliers and hook the top of the 'C' shape into
the seat cover wire.  Then get the hook and pick up the wire
embedded in the cushion.  Then LUNGE - pull the cushion wire up, at
the same time as pushing down with the pliers, and hook the cushion
wire into the bottom of the hog ring 'C'.  Then, with a smirk, just
squeeze the pliers shut.  Takes seconds with practice, and produces
a really tight seat.

It's called "The Hawg Ring Lunge".

If any Area Co-ordinators want to arrange workshops to do this over
the winter, tool loans could be arranged.

The Throttle Stop Screw

On many types of car, the throttle stop screw (the screw and
locking nut that the throttle quadrant sits against when closed) is
a means of idle adjustment.  It isn't on an ur-quattro -it's a
means of compensating for manufacturing tolerances and is set for
life in the factory.  The microfiche is quite explicit - if the
screw is moved, the throttle body must be returned to the factory
to be reset.  On some cars, Audi have deliberately broken the top
of the screw so it can't be moved.

Not a hose - a part

On the MB engine, there's a short hose connecting the inlet
manifold to the cylinder head - it supplies unthrottled air to the
injector shrouds to cool the injectors and improve the spray
pattern.  It's actually not just a hose - there's a constrictor
fitted in the middle of it, and it has its own part number - 034
191 491T.

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--
 Phil