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Discussion Starter · #1 ·
Hi I have a 2002 lexus is300 and my fuel pump has low voltage. It also will not prime. I Have no idea what’s happing I’ve had other people look at it and they also have no idea. Does anyone know or have an idea what’s happening. I’ve already replaced the relay but I think that’s all.
 

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Hi I have a 2002 lexus is300 and my fuel pump has low voltage.
How many Volts are you getting between the Blue/Red stripe fuel pump power wire and chassis ground when you key-on the car?

I just have no idea where the wires run too becuase they go into a huge bundle of more wires
That is why you need to review and understand the wiring diagram, which spells out every wire in the car, its color, and location.

For power to get to the fuel pump, it must pass thru the EFI Relay, then the Circuit Opening Relay. With just these two relays closed, power can pass thru the Fuel Pump Resistor and on to the fuel pump; albeit at reduced voltage.

The ECU is programmed to open/close the Fuel Pump Relay to either allow full voltage to the pump (FPR closed) or reduced voltage (FPR open).



If I were you, I would first check and/or replace the Fuel Pump Relay. After verifying it is working correctly, if the pump is still not getting 12.5V, I would bypass the fuel pump resistor. The fuel pump resistor is the finned heat-sink unit with a little metal heat shield over it, located just aft and slightly above the ECU box.
 

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Side question, is there a problem you are trying to diagnose that is making you measure the voltage? Is the car having a fuelling issue?
 

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Discussion Starter · #9 ·
How many Volts are you getting between the Blue/Red stripe fuel pump power wire and chassis ground when you key-on the car?



That is why you need to review and understand the wiring diagram, which spells out every wire in the car, its color, and location.

For power to get to the fuel pump, it must pass thru the EFI Relay, then the Circuit Opening Relay. With just these two relays closed, power can pass thru the Fuel Pump Resistor and on to the fuel pump; albeit at reduced voltage.

The ECU is programmed to open/close the Fuel Pump Relay to either allow full voltage to the pump (FPR closed) or reduced voltage (FPR open).



If I were you, I would first check and/or replace the Fuel Pump Relay. After verifying it is working correctly, if the pump is still not getting 12.5V, I would bypass the fuel pump resistor. The fuel pump resistor is the finned heat-sink unit with a little metal heat shield over it, located just aft and slightly above the ECU box.
I will try this. I replaced the fuel pump relay and it didn’t fix it so I’ll try to bypass the resistor. Is there anything else I should know?
 

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Discussion Starter · #12 ·
How many Volts are you getting between the Blue/Red stripe fuel pump power wire and chassis ground when you key-on the car?



That is why you need to review and understand the wiring diagram, which spells out every wire in the car, its color, and location.

For power to get to the fuel pump, it must pass thru the EFI Relay, then the Circuit Opening Relay. With just these two relays closed, power can pass thru the Fuel Pump Resistor and on to the fuel pump; albeit at reduced voltage.

The ECU is programmed to open/close the Fuel Pump Relay to either allow full voltage to the pump (FPR closed) or reduced voltage (FPR open).



If I were you, I would first check and/or replace the Fuel Pump Relay. After verifying it is working correctly, if the pump is still not getting 12.5V, I would bypass the fuel pump resistor. The fuel pump resistor is the finned heat-sink unit with a little metal heat shield over it, located just aft and slightly above the ECU box.
So what all would I need to do to bypass the resistor?
 

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So what all would I need to do to bypass the resistor?
On the schematic I posted, it shows two wires going to the fuel pump resistor: Green/White-stripe and Blue/Red-stripe. You'll see a two-wire pigtail (with those color wires) going to the fuel pump resistor. Unplug the resistor and put a jumper wire across the two pins in the harness pigtail. Use 14 or 16 AWG wire for this, as it will have to carry the full current for your fuel pump.
 

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Discussion Starter · #14 ·
On the schematic I posted, it shows two wires going to the fuel pump resistor: Green/White-stripe and Blue/Red-stripe. You'll see a two-wire pigtail (with those color wires) going to the fuel pump resistor. Unplug the resistor and put a jumper wire across the two pins in the harness pigtail. Use 14 or 16 AWG wire for this, as it will have to carry the full current for your fuel pump.
I did that and it helped. Car was firing more but still not start
 
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