mysterious bogging down

[quk@sievers.com (Phil Payne)]

In message <UPMAIL06.199702270410180883@msn.com> "Matt Harger" writes:

> Last friday I sent a message about my '86 Quattro 4000 (with '87 engine) 
> having troubles "bogging down" after a few minutes of driving.

The first place I would be tempted to point the finger is the warm-up regulator 
valve.  If you don't know what this is, follow the two braided fuel lines 
across the top of the engine - they go to the valve.
 
Its job is to feed a pressure back to the metering head.  The "feed" line takes 
system pressure to it, at around 6 bar or so.  On the way back, the pressure 
(once warm and comfortable) should be 3.4 bar or so.  The typical failure mode 
is leakage, allowing greater pressure back to the metering head.  This pressure 
acts downwards on the metering head's plunger, reducing fuel flow.
 
The warm-up valve, despite being bolted to a hot engine block, is principly 
electrically heated.  There are about six different designs, and I think the 
'86 4000 has a vacuum line attached for full throttle enrichment.  At the lower 
front end of the valve, there's a plastic dust cap - check this rotates.  Check 
that the vacuum line is in good order.  If all that is OK, I suggest you get a 
competent fuel injection mechanic to check the valve.  This is done with a 
specialised gauge that goes in the return line.  It has a valve, and it's then 
a simple matter to close the valve and read system pressure, then open it and 
read control pressure.  A competent mechanic could do the measurement in half 
an hour.

But I would certainly suggest you find a "Bosch" mechanic rather than an "Audi" 
mechanic for a problem like this.

Changing the injector seals is trivial - it's one of the cheapest parts on an 
Audi and takes a few minutes.  Well worth doing on a ten-year-old car.  Most 
shops over here will insist on examining the injectors in any case, and new 
seals are only pennies.

--
 Phil Payne
 phil@sievers.com
 Committee Member, UK Audi [ur-]quattro Owners Club