Fuel System
Fuel Pump Delivery Rate Checking
This guide is preserved from Clark's Garage, a foundational 944 resource. View the original →
Tools you'll need
- VAG 1669 / KTS 500 DME Diagnostic Adapter
- Durametric / Foxwell NT630+ Durametric Diagnostic Software
- Bosch / OTC Fuel Pressure Gauge — 0–6 bar
- Fluke 117 / Klein MM400 Digital Multimeter (4000+ count)
See the full tools list for where to buy each one and budget alternatives.
Tools
- Metric Wrench Set
- Measuring Container (1500 ml / 50 fluid ounces or larger)
- Hose to connect to the fuel pressure regulator
- Hose clamp
- Stopwatch or other timing device
- Catch Rags
Procedure
NOTE
Be sure to have rags ready to catch excess fuel when disconnecting fuel lines / caps. The fuel in the fuel rail may be under high pressure and may spray if the fuel rail cap or lines are removed too quickly.
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Slowly disconnect the return line from the fuel pressure regulator (FPR) going back to the fuel tank.
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Using a hose clamp attach a hose to the discharge of the FPR that is long enough to reach the measuring container.
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On early cars (pre-1985.5), remove the fuel pump relay (located under the dash on the driver’s side (left-hand drive)).
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On late model cars, remove the DME relay located on the fuse / relay panel under the hood.
NOTE
Be prepared to start the timing device as the fuel pump will start as soon as the jumper is installed.
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On the panel where the relay was removed (early or late model), jumper terminals 30 and 87b. The fuel pump should start. Start the stopwatch as soon as you hear the pump start running. If you aren’t sure which terminals are the correct ones, refer to the terminal number labels on the bottom of the relay.
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Allow the pump to run for 30 seconds and then remove the jumper to stop the pump.
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Determine the amount of fuel collecting in the measuring container and compare to the table below.
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Values significantly below those listed indicate a problem with the fuel pump, fuel filter, or fuel dampener.
Fuel Pump Delivery Specifications Most Fuel Pumps 850 ml / 30 sec. (28.7 fluid ounces) Pumps With Green Paint Code Bosch No. 0 580 464 028) 750 ml / 30 sec. (25.4 fluid ounces)