Those with bad idle, intermittent missing and stumbling on acceleration...
may want to take a serious
look at that little pic I posted Saturday related to the badly cast step in the
cylinder head inlet port.
Yesterday afternoon I made a mickey mouse fixture for testing an injector by
running fuel from my car-mounted FPR to my spare intake manifold and the
remaining unmodified AAH head. I ran power leads to the injector and pulsed it
while trying to catch the fuel as it ran out in a 5 gallon plastic pail below.
I may never be able to get the gas smell out of the garage!! I was afraid to
even turn wall switches on/off due to internal arching.
With stock ultrasonically cleaned injectors it was ugly. The inverted cone
shaped spray pattern was completely compromised by the projecting lip in my
pics that caused the spray pattern from the
Next I tried it with one of my RC Engineering injectors. The RC's are known for
their narrow stream, more tightly focused spray pattern. And true to that they
didn't disappoint. They injected all their fuel straight into area that would
be the back side of the valve head when there's a valve in the head. There was
no subsequent streaming or large drops that followed the fuel pulse.
While this isn't an endorsement for RCE injectors I have to say that there is a
reason they work so well and offer so much better power, better idle quality
and acceleration in an unmodified 2.8 intake runner. Due to their jet stream
spray pattern compared to the Audi injectors cone/fan spray pattern they get
all of their fuel past the step I posted pics of Saturday. The Audi injector
loses 50% of it's cylinder feed thru deflection, streaming and puddling which
keeps fuel out of the cylinder until after the intake valve is long-closed.
Then it pulls it in on a non-compression stroke and blows it out the exhaust as
non-burned fuel. "May" be why the 12V suffers so much
burbling/backfiring on deceleration. May also be why the intake valves get so
carbon'd up on this motor since very little fuel can hit them in any semblence
of finely atomized spray patter. And why out exhaust tips are always so sooty
and black.
This phenomenon could very easily cause continual idle fluctuations, stumbling,
surging on acceleration, especially in 3rd gear as well as bad gas mileage,
poor power and diminished acceleration. Basically the par equivalent of a 50%
clogged injector that you can never get clean... only worse as it's not clogged
but the fuel is never getting into the cylinder on a compression stroke but
rather on a non-firing stroke and dumped out the exhaust as wet fuel only to
cause exhaust pipe detonation when it contacts a hot catalytic element.
As I said before; This is Bad Audi, BAD BAD!