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WERK I WERK I is offline
Forced Induction Junkie
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Join Date: Jan 2003
Location: Wisconsin
Posts: 3,302
The rear pump is in series with the front pump so you can never experience a higher fuel pump pressure from the discharge of the rear pump compared to the discharge of the front pump. The rear pump insures the high pressure/fuel flow required is delivered to the CIS system.
A healthy CIS system is dependent upon other components performing as Bosch intended. How's the fuel filter? An old fuel filter will restrict fuel flow dropping fuel pressure/flow to the fuel distributor.

BTW, measuring the voltage at the rear pump with the wires disconnected will tell you nothing in terms of the health of the pump. You have to measure the voltage at the pump to see how much voltage is dropping when its running. These pumps tend to get pretty noisy when on they're last legs. You can hear a bad pump whining from standing a few feet away.

I suspect the Warm Up Regulator is not adjusting the Control Pressure adequately with higher boost levels. A CIS Pressure testing set of gauges will bring that out if true.
'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
Old 05-06-2013, 12:38 PM
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