No Flow through Pressure Regulator

SJ syljay at
Wed Feb 4 22:38:48 EST 2004

Sounds like a bad fuel pump to me. If the fuel pump is not putting out
enough pressure, the pressure regulator acts as a closed valve. System
pressure is around 90 lbs. If the pump only puts out 80 lbs, the pressure
regulator wont open . . . no fuel flow thru it.

If you had an air compressor, set it to 100 lbs, blow air into the input
opening . . .air will rush out the other end. Set air compressor to 75 lbs,
no air will travel thru the regulator. This is a quick check if you have
access to air compressor.

Since you have it all apart, why not try the fuel pump flow test? The test
may not be valid because the pump isnt fighting against the pressure
regulator. But, the test is easy to do.
You should get at least 750 cc in 30 seconds. Use the tables that I sent you
for more accurate figures.

85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q

> From: "Marc Boucher" <mboucher70 at>
> Today's update:
> 1.) Cleaned the DPR thoroughly...found a plastic hose that fit snugly into
> one hold of the DPR and can confirm that there is clear passage through
> DPR...i.e. it is not clogged.
> 2.) Energized fuel pump, saw fuel flowing out one of the holes from the
> distributor that goes to the DPR.
> 3.) Reattached DPR.
> 4.) Detached return hose.
> 5.) Energized fuel pump.  Same result as before.  No output from return
> hose..Pump slows to a crawl as pressure builds up with no where to go.
> 6.) Detached, small pipe at the pressure regulator.  Energized fuel pump.
> Confirmed flow out of pipe.
> 7.) Reattached small pipe and detached thicker pipe at the pressure
> regulator.  Energized fuel pump.  Confirmed flow out of pipe.
> Thus fuel distributor and both lines that flow into the pressure regulator
> are flowing but nothing is coming out of pressure regulator.  Thus either
> the pressure regulator is clogged or bad, or the fuel pump isn't pumping
> sufficient pressure or both.
> I've filled the pressure regulator with carb cleaner and have it sitting
> a sealed glass container.  I'll leave it soaking overnight and reattach
> tomorrow.  Someone mentioned that they had an adjustment screw.  This one
> does not.  And its the only part that I've seen that doesn't have "Bosch"
> (or any other brand) stamped on it.  One end attaches to a plastic hose
> leads to a large container near the right fender.  I assume that fills
> air in order to keep pressure when the car is shut off?  I'm assuming
> there's no benefit to filling that end of the regulator with carb cleaner.
> Marc

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