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Join Date: Apr 2009
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930 shop manual

Have been pondering pages 20-2 and 20-3 in the 930 shop manual. Everything makes sense up to CHECKING PUMP PRESSURE. It looks like the pictures are of 2 different pumps (would make sense) with 1 hook up of the tester testing both pumps at the same time. Like magic.

Also, one might be inclined to think that the fuel delivery test point on top of the fuel filter would be a better place to test pressure. Checked mine and it was 1.25 bar.

79 930 unmoded as far as I know
Old 05-22-2014, 07:04 PM
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Between the pumps is correct, and the spec is between 2 - 4 bar IIRC.
Why?
If the pressure is <2bar, the front pump is not doing its job pushing fuel to the back of the car.
If the pressure is >4bar, the rear pump is not doing its job relaying the fuel to the engine, and fuel is backing up.
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Old 05-23-2014, 10:16 AM
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Garage
If the rear pump is pumping greater than 4 bar, how would that affect the way the motor runs? What symptoms might it exhibit? Thanks , Wayne
Old 05-23-2014, 11:18 AM
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The rear pump output should be over 4bar -- that's your system pressure, 6.0-6.6bar IIRC (varies slightly by engine year).

So testing is as follows:
1) check voltage at both pumps, compare to battery voltage
If bad, fix it -- fuse, relays, wiring... whatever is bad.
If good, proceed.
2) check pressure between the pumps to verify functionality of pumps.
If out of space, replace the suspect pump.
If good, proceed.
3) check system flow
If low, find the source of your restriction.
If good, proceed.
4) check system pressure

Then check control pressure.

Then injectors.
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Old 05-23-2014, 11:24 AM
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