Fuel System Mysteries

[Alexander van Gerbig]

    Well the turbo upgrade has brought up some fuel system issues I didn't
know existed.  Here are the symptoms:

1. Low idle at 800rpm
2. Airflow plate potentiometer U2 voltage when engine is on is way too high
(plate is resting too high at idle)
3. Under initial acceleration DPR current goes down when it should go up
4. WOT switch is not triggering proper DPR current, WOT switch is working
properly

The idle I can't seem to raise.  I used to be able to make fine idle
adjustments by changing the base timing a degree or two, that doesn't work
now.  When I open the idle bypass screw the idle goes bonkers, up and down,
simulated vacuum leak.  Anyone?

The U2 voltage, engine off, of the airflow plate is properly set.  The U2
voltage, engine on, is too high.  The range specified for my U2 voltage with
the engine on is around 0.5v to 0.7v, I get 1.1v.  So I checked my basic
airflow plate position and found there was a bit too much free play.  I
adjusted the plunger seal clearance on the metering head and decreased the
free play to around 1.5mm, middle range of spec.  That dropped the U2
voltage when the engine is on to 1.0v, but still way above spec.  I don't
understand what the deal with that is.  I am going to adjust the
potentiometer trim screw a bit and see what I can get that down to.  Anyone?

When I rev my engine without load I should get a small bump in DPR current,
but I don't.  I get a slight negative current.  The idle mixture is within
spec so this makes little sense.  Anyone?

The WOT switch ain't working right.  For testing in the fuel system Bentley
book it says to rev the engine to 4k rpm and close the WOT switch.  The
result should be a 9-19mA current, but I get no change.  Am I going to get
the car on the road and watch my DPR current under WOT and see what happens.
I am also going to minimize boost majorly, like 2psi or so until I get these
fuel system problems figured out.

Any suggestions are greatly appreciated!

Thanks!

Alexander van Gerbig -- '88 80t

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