I have determined that the digifant system on my 1988 Vanagon does not like any setting but STOCK settings.

I advanced my AFM up two notches and it ran OK but I had a small off- idle
hesitation, I thought that I just needed to adjust something else.
Well, I then decided to move the spring tension a total of four notches
lighter (As suggested by someone else.) My idle hesitation only got worse and
the top end power did not increase but went down some

The higher AFM readings caused the ECU to dump more fuel, while the o2 sensor
tried to lean it out and could not so the ECU basically ignored the readings
and reverted to default valves programmed into the chip not the actual
readings from the various FI parts.

Well I moved it back and the idle was instantly better and there was more
power in RPM range.
The gas mileage increased 3 mpg even with lowering the front tire pressure 10
psi to 30 psi.

-Fuel pressure set at 36.5
-New AFM set to my original 88 AFM settings. (One notch lighter tension than
the new replacement AFM)
-New VW o2 Sensor- (splice in did not work correctly for me, my ECU ignored
it)
-New Idle control unit (behind rear light)
-Timing set as specs call for: on notch on pulley

I tried to advance the timing and each time the engine ran the same or worse.
I have increased the fuel pressure to +40 psi, no power increase.
I have adjusted the co to exactly three turns: any more or less and the
engine runs hotter.

I think that trying to tricking the ECU into giving more fuel only throws the
delicate micro-electrical balance the ECU maintains off, causing problems OR
masquerading FAILED parts. The ECU is good at continuing to run with failed
components, but to a point.

The FI system is juggling the delicate balance between lean and rich
conditions to obtain the perfect balance.  When a part fails or adjustments
are made outside the range of the ECU, default values are used instead of the
actual readings.

If you have had OK power and it starts to fall off, chances are a part is out
of spec or has failed and then trying to trick the ECU can only make matter
worse, while it seems to have been “cured”, because when the part
then could fully fail or another part could fail in the future leaving you
stranded in the middle of nowhere….

I have had the cold idle cut off problem- caused by out of adjustment parts
so the ECU did could not set the proper cold idle-it thought it was already
warm and the cold engine did not run until warm—I do not have that
problem any more.

I had the low-end and high end power suffer due to the AFM being too
loose—2 notches looser caused the problem, four made it worse.

Conclusion:
If you want more power: Check that ALL FI parts are functioning as VW created
them to (or aftermarket), OR add parts that increase the power, OR rebuild
the engine to incorporate parts to make it faster...do not try to fool
(mother) Digifant…

I am sure the system is much more complicated then my attempts to explain it,
but all the parts work must in harmony for the system to function as
designed, attempts to short cut can come back to haunt…

***The report is my personal experiance, with my 1988 Vanagon Wolfsburg with
my modifications done to the engine to make it run better and my attempts to
work out FI problems from the PO.

Robert

DF running good for now...