URQ fuel pressure

[isham-research.freeserve.co.uk at pop.pol.net.uk]

> If one finds that the fuel pressure is not to spec, what are the ways of
> controlling it other than the FPR, and the fuel pump itself.

On an MB ur-quattro this is not adjustable - system pressure is determined
by an external and (for this purpose unadjustable) system pressure
regulator.  Scott Mockry has pointed out that this device (used on
US MC-1 and MC-2 engines in the 5000 series) _does_ have an adjustment
but it's related to residual pressure maintenance - you demount the
valve and shove a 4.5mm Allen key right down inside it.  My empirical
experience is that adjusting the residual pressure tends to fix the
system pressure too.

Anyway - back to _YOUR_ car, which I assume is a WR or WX ur-quattro.

(Same instructions apply to any car using the -147 metering head -
 check the green Bosch plate on the rear of the head.)

Audi do a kit of parts - 035 198 685 - which includes a new plunger,
O-rings and shims.  Should be around $30 or so.

Pack the space below and behind the metering head with rags.  Run the
fuel pump to get pressure up in the system, then switch it off.  Undo
the largish hex nut (same as the head of the plunger in your spares kit)
on the back of the metering head and remove the plunger.  If there is
still residual pressure in the system, fuel will spray out - but it will
also bring with it the piston that sits on the end of the plunger.  DO
NOT DROP IT ON A HARD SURFACE - hence the rags.  If it doesn't come,
fish it out with a small magnetic retriever tool.

Using a small magnifying glass, check out the O-ring on the end of the
piston.  It may have a round or a shield-shaped cross section - there
are replacements for both types in the kit, but it's important to fit
the right one.  Slip it over the retaining ring with a blunt needle.

Refit the piston.  Check the shims on the removed plunger and fit two
more to the plunger going in.  Each shim is worth about 0.2 bar
system pressure - if it's wrong after you reassemble it, adjust by
adding or subtracting shims.  You may need quite a few in an old head.

If you have cold start problems with the car, it's worth cleaning out
the piston's seat with pipe cleaners.  I've also been known to 'pulse'
the fuel pump with the plunger and piston out, just to clear any
crap sitting in there against the piston seat.

--
 Phil Payne
 UK Audi quattro Owners Club
 Phone +44 7785 302803   Fax: +44 7785 309674