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Discussion Starter · #1 ·
Guys
Since I bought the car, the fuel pump never work. It’s being wired directly thru an aftermarket relay.
I would like to revive the OEM fuel pump system for safety, in case of an accident.
I checked Resistor pack with multimeter and it reads 0 ohm. The Relay passed the test. BGB recommendation is to replacement of the resistor.
Any body has one for sale? I don’t want to post a thread and get all the scammers.
 

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The BGB lists the resistor as 0.73 ohms (i.e. less than 1 ohm). Just wanted to be sure you knew how low the resistance value was. Most of my HF multimeters are not accurate enough to reliable check this (I have better meters).
 

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Guys
Since I bought the car, the fuel pump never work. It’s being wired directly thru an aftermarket relay.
I would like to revive the OEM fuel pump system for safety, in case of an accident.
I checked Resistor pack with multimeter and it reads 0 ohm. The Relay passed the test. BGB recommendation is to replacement of the resistor.
Any body has one for sale? I don’t want to post a thread and get all the scammers.
I think you are confused about how the systems work.

The ECU controls the fuel pump for safety but has a secondary speed system that the ECU also controls but does not relate to safety.
 

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Discussion Starter · #5 ·
I think you are confused about how the systems work.

The ECU controls the fuel pump for safety but has a secondary speed system that the ECU also controls but does not relate to safety.
I read some where on this forum, In an event of accident when the motor shut off but the key is in IGN position, the FPR and Resistor will cut off fuel.
They way I have the aftermarket relay set up, the only way to turn off the fuel flow is to physically turn the key to off. We assuming that the fuel line is ruptured I accident.
 

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The ECU will have an "FP" line which is used to ground (close) the Circuilt Opening Relay (COR) to allow power to flow to the fuel pump. The COR also has a 2nd terminal / coil that also closes it when the car is cranking.

The "Fuel Pump Relay" is for controlling high/low power mode of the fuel pump. In low (normal) mode, power flows through the resistor, thereby limiting power at the pump. In high mode the Fuel Pump Relay switches and power flows directly the pump, bypassing the resistor. The ECU determines when high mode is needed - presumably high boost and/or high rpm.

Some folks eliminate the FPR and the resistor and just run their pump in high power mode all the time.
 

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Discussion Starter · #7 ·
The ECU will have an "FP" line which is used to ground (close) the Circuilt Opening Relay (COR) to allow power to flow to the fuel pump. The COR also has a 2nd terminal / coil that also closes it when the car is cranking.

The "Fuel Pump Relay" is for controlling high/low power mode of the fuel pump. In low (normal) mode, power flows through the resistor, thereby limiting power at the pump. In high mode the Fuel Pump Relay switches and power flows directly the pump, bypassing the resistor. The ECU determines when high mode is needed - presumably high boost and/or high rpm.

Some folks eliminate the FPR and the resistor and just run their pump in high power mode all the time.
So, it’s safe to eliminate the the FPR/Resistor?
 

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So, it’s safe to eliminate the the FPR/Resistor?
Yes. The NA cars never had this dual speed function and plenty of swaps run like this. It's to stop more fuel than needed running through the engine bay getting heated. Due to the wiring for it being part of the body harness in a turbo you generally wouldn't install it to an NA.

Just to clarify with @JimKing comment. The pin on the ECU is FC rather than FP. Fuel cut. His description is correct on how both systems work.
 

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The OEM system is super confusing in how it's all named. The "fuel pump relay" should be called the "fuel pump SPEED relay". That's all it does, switch the pump from low (running through the resistor) to high. The actual fuel pump on / off relay is the "Circuit Opening Relay".
 

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Personally I think keeping the resistor is a better idea, it will reduce wear on the pump not having it run full speed all the time. That being said, my first SW didn't have it and ran just fine.
 

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Personally I think keeping the resistor is a better idea, it will reduce wear on the pump not having it run full speed all the time. That being said, my first SW didn't have it and ran just fine.
It's not there to reduce wear on the pump. It's to stop extra fuel and electrical load when not needed.
As an example some 2GR run this system while others do not. Fuel pumps are very reliable items from DENSO. Mine is still running in the NA 32+ years later and it runs full speed.
 

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And to reduce pump noise at idle when you are most likely to be able to hear it. Especially in a car like the MR2 where it's right under your elbow.

Actually, does it even reduce electrical load? Since it's a resistor dropping the voltage, the extra power is just getting dumped into the resistor as heat.
 
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Do not confuse the safety function with the high output function. The fuel pump resistor and its associated relay switch the fuel pump between normal and high output mode. It has nothing to do with safety. The Circuit Opening Relay is controlled by the ECU and turns off the fuel pump if the engine stops turning for any reason.

If your aftermarket relay is not getting power from the Circuit Opening Relay, you have bypassed the safety function.
 

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And to reduce pump noise at idle when you are most likely to be able to hear it. Especially in a car like the MR2 where it's right under your elbow.

Actually, does it even reduce electrical load? Since it's a resistor dropping the voltage, the extra power is just getting dumped into the resistor as heat.
Well now that you put it into words like that, electrical load does not change. I've not been able to hear the pump in my car but it's been awhile since I had a stock muffler on it so that's probably why.

@mtang65 so what is it that we are trying to fix on your car? Can you show us the setup with the aftermarket relay and where it is wired in to make it work?
 

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Discussion Starter · #15 ·
Well now that you put it into words like that, electrical load does not change. I've not been able to hear the pump in my car but it's been awhile since I had a stock muffler on it so that's probably why.

@mtang65 so what is it that we are trying to fix on your car? Can you show us the setup with the aftermarket relay and where it is wired in to make it work?
Rectangle Font Parallel Schematic Diagram

This is the set up I’m running with.
I’d like to have the idea that the fuel pump shut off in an event of fuel line ruptured in an accident.
 

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Discussion Starter · #16 ·
Do not confuse the safety function with the high output function. The fuel pump resistor and its associated relay switch the fuel pump between normal and high output mode. It has nothing to do with safety. The Circuit Opening Relay is controlled by the ECU and turns off the fuel pump if the engine stops turning for any reason.

If your aftermarket relay is not getting power from the Circuit Opening Relay, you have bypassed the safety function.
OMG! I got it. It’s so simple. I will run power from C.O.relay to my Aftermarket relay. Thank you!
 

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Actually, does it even reduce electrical load? Since it's a resistor dropping the voltage, the extra power is just getting dumped into the resistor as heat.
Yes it does. I = E/R. Increase R (by adding a resistor in-line with the pump) and you decrease current. E (voltage drop across both loads) remains the same.
 

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OMG! I got it. It’s so simple. I will run power from C.O.relay to my Aftermarket relay. Thank you!
Just use the power wire that would normally power the fuel pump to trigger the aftermarket relay. This is a semi common mod, the stock wiring is a bit under sized and causes a voltage drop, reducing power to the pump. It's fine with the stock pump, but with an upgraded pump it's marginal.
 

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OMG! I got it. It’s so simple. I will run power from C.O.relay to my Aftermarket relay. Thank you!
Question is, why do you need the aftermarket relay? Where is it located?
Like @Alex W mentions, you can use the old pump power wire to activate the new relay. I have done this for a mates car where we are running a DW300 340lph pump with significantly larger wiring.
For me I might end up upgrading the OEM wiring which will be a mission but worth if for my OCD.
 

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Discussion Starter · #20 ·
Question is, why do you need the aftermarket relay? Where is it located?
Like @Alex W mentions, you can use the old pump power wire to activate the new relay. I have done this for a mates car where we are running a DW300 340lph pump with significantly larger wiring.
For me I might end up upgrading the OEM wiring which will be a mission but worth if for my OCD.
I was not able to get the OEM FPR system to work. Another used OEM relay I got from eBay still didn’t fix the problem. I spent a lot of time tinkering with this issue, got sick and tired of it and just left it alone. Then I found the diagram on how to wire a relay to a fuel pump and I’ve been running with it. So, now I got time on my hand and trying to go at it again to see if I can get the OEM FPR back to functionally.
I’m not getting any power on FPR plug pin 3 when key in IGN.
Rectangle Slope Font Parallel Diagram
 
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