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mysterious bogging down
In message <UPMAIL06.firstname.lastname@example.org> "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
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.
Committee Member, UK Audi [ur-]quattro Owners Club