RRE Fuel Pump Tech Tips
Voltage vs. Flow
In 1996 we did some research into Denso's (formerly Nippon-Denso) in-tank fuel pump flow rates. The biggest surprise was how much voltage affects flow. Also how much flow drops off at higher pressures.
If you measure the available voltage at the battery with the engine running you should see 13.5-14 volts or so. If you then measure the voltage at the fuel pump it's self with the engine running, it will be around 11.9 v and with the fuel pressure regulator loaded with boost pressure the voltage drops to 11.8 v. This is from the small gauge factory wiring being unable to handle the current. The fix for this is to run a large (10 ga. or more) wire directly from the battery to the fuel pump.
To do this you'll need a 30 amp relay (Bosch part #0 332 204 150 or Hella part # 960 388 07 or Porter & Brumfield # VF4-45F11) and the relay wiring harness for it. Any 30 amp 12v relay will work. Try an alarm shop or stereo shop if you have difficulty finding the correct relay. We use a heavy-duty fuse holder with a 30 amp fuse right off of the positive terminal of the battery. Attach the fuse holder to the positive terminal of the battery. The other end of the fuse holder goes directly to terminal #30 (power in) on the Bosch style relay. From terminal #87 (power out) on the relay run the big 10 ga. wire back through the fire wall, under the carpet towards the back of the car. The color for the positive wire to the fuel pump will vary some from year to year. The wire color also changes from one side of the connector to the other. On the car side of the connector the wire will almost always be black with a white stripe. Occasionally it is blue with a white stripe. The large all black wire is always ground. The positive wire will be the other thick wire. Smaller yellow wires are for the fuel level gauge and the low level warning light. Once you go on the fuel pump side of the connector, the positive wire is usually blue.
Front wheel drive (1G) '89-'94
Run the wire to the driver side rear seat floor. Pull out the seat bottom and pull back the carpet where the back seat passenger would put their feet. You will see a wire harness running through to the fuel tank area. Poke the new fuel pump wire through this grommet. Go under the car now and carefully run the wire along the other wires and cables with zip-ties. You need to route the wire to the rear center of the fuel tank. There is a round black connector with 2 wires, cut the blue wire and connect the new larger wire to the wire running into the fuel tank. Tape up and protect the unused old wire.
AWD (1G) '89-'94
Continue running the new larger wire all the way (inside the car) to the driver's side rear corner (driver side of the spare tire). There is a plate that unscrews to access the fuel pump, remove it. Cut a small hole through the grommet and run the wire through the hole. Cut the black wire with the blue stripe and connect the new larger wire to the wire running into the fuel tank. Tape up and protect the unused old wire.
FWD and AWD (2G) '95-'98
Lift up the rear seat bottom cushion. On the passenger side there is a metal plate screwed on, remove it. Cut a small hole through the grommet and run the wire through the hole. Cut the black wire with the blue stripe and connect the new larger wire to the wire running into the fuel tank. Tape up and protect the unused old wire or use it to trigger the relay.
An easy way to trigger the relay is to use the fuel pump check connector located on the wiring harness that runs along the firewall. You will see a single black connector that is taped to the wire harness near the battery. This connector gets power when ever the fuel pump should be on. Run a wire from this check connector to terminal #85 on the relay. From terminal #86 run a ground wire. If your relay also has a terminal #87A, ignore it (not used). Use care with all connections that you make, these are important wires !
1G AWD all 2G
You may find it simpler to install the relay close to the fuel pump. An easy way to trigger the relay is to use the old fuel pump voltage input wire to trigger the relay. The old small wire gets connected to terminal #85 on the relay. From terminal #86 run a wire to ground. Tuck the relay under the safely under the plastic 1/4 panel inner trim.
With this modification you should see 13.8-13.9 volts at the pump with a good charging system. This allows the pump to pull an additional 5 amps at idle. The electrical system is designed to operate at this (14 v) voltage. Denso fuel pumps are designed with this voltage in mind.
As you look these specs over you can see how it is worthless to
compare fuel pump flow with out specifying both voltage and pressure.
Lph = liters per hour. All Denso 50mm (1G) and 38mm (2G and GVR4) Dia.
in-tank fuel pumps start out with the part number 195130-xxxx