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12v mod with relay.


Guest Poopra1

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Guest Poopra1

I have a 1995 jdm supra with the 2jzgte

 

I recently replaced my fuel pump with a 450lph walbro and also added the 12v mod with relay. The car runs great but when at idle sometimes i can hear the relay clicking, i also notice it when i release the gas while crusing (no load on motor) as im coming to a stop. Is this typical of the mod?

Edited by Poopra1 (see edit history)
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I've always thought the 12v mod relay or not, is a bad idea. The purple and green wires are not switched outputs.

 

 

Is there a description of the control circuit's functionality anywhere? It's a mod I see done quite often, but not one I have done myself. I had assumed they were taking a switched output from the main ecu and using it to control a relays solenoid coil. The relay would then bypass the fuel ecu and its voltage regulation strategy, feeding the pump a fixed 12V based on the state of the main ecu control wire.

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My understanding of the 12v mod is bypassing the ECU and connecting the Blue/Orange and Blue/Red wires directly. The Relay is just using the Red/Orange to drive the relay 86 terminal and making a new power line to 30 and a from 87 to the pump. The small ground wire to the ecu being the ground to 85.

 

Green is DI (Diagnostic Interface) back to the Engine ECU

Purple is FPR (Fuel Pump Relay - legacy name of old I guess for continuity) and is the voltage control line from the Engine ECU.

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So really what people are seeing is the relay coil dropping out when this voltage drops below the hold in level....?

 

Needs a little box `o' tricks to give a high / low output from it then to drive the relay. Hmmmm...

 

If they are using the purple wire to drive the relay 86/85 side, yes, most probably. The diagrams I've seen where a relay is used are just using the blue/orange wire as the relay 86 12v trigger and a new battery feed to 30 and 87 to the pump via Blue/Red. with the white/black as ground (85). The thing I never liked was the pump is running as soon at you key on.

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The 12v mod with relay Nod is for that exact reason, the pump primes as normal when key turns to on but then goes off as normal until key is turned to start the car.

 

The one you are talking about is the 12v mod before it got improved to have the relay.

 

I see, so you are using the FPE as a relay to run a relay. That relies on the Relay switching voltage to be 9v or lower which might explain why some people have a clicking issue as this can't be guaranteed.

Edited by Nodalmighty (see edit history)
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I don't understand the 12v mod, is this needed for all fuel pumps? I've just fitted a 255 walbro and the car runs fine?

 

And of course, if it's not relayed it will remain constantly powering the pump in the case of a accident which is not what you want at all.

 

Or is it only the larger pumps what need this?

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Aeromotive pumps won't run properly without this modification to the power supply either.

 

You can start the car and it will tick over until the tank runs dry but as soon as you try to increase the engine speed it just stalls.

 

Haven't had any issues with the set-up in a couple of years, the Aeromotive unit was bought to replace a new Walbro 255 that seized solid after 6 hours of use.

 

My car does idle like a pig most of the time and sometimes cuts out on the way back into the paddock when at very low speeds with the clutch pressed, but I've always put that down to the idle control valve being in need of attention.

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I started this thread some time ago in regards to this

http://www.mkivsupra.net/vbb/showthread.php?272714-12v-mod-will-this-work

 

the reason for the 12v mod with relay is to keep the stock fuel ecu funtions and still be able to run the 400 series walbros, using the 9v out for the relay coil and the 12v as the feed .the reason you hear it drop out is due to the 9v not being enough to hold the coil but as soon as it drops it then has the power to reingauge the relay .

you need a lower voltage drop out relay so once switched it holds until a lower voltage like 6v

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Im about to install a walbro 450LPH fuel pump and Im a bit confused. Going to pull a new cable from the battery but what relay should I use and is the 12V mod needed? A drawing would be nice, how the relay should be hooked up?

 

Would this work? http://www.ebay.co.uk/itm/Fused-On-Off-Automotive-Fused-Relay-12V-30A-4-Pin-Normally-Open-Car-Bike-/252048082683?hash=item3aaf3c86fb:g:FswAAOSwMmBVwl5w

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Im about to install a walbro 450LPH fuel pump and Im a bit confused. Going to pull a new cable from the battery but what relay should I use and is the 12V mod needed? A drawing would be nice, how the relay should be hooked up?

 

Would this work? http://www.ebay.co.uk/itm/Fused-On-Off-Automotive-Fused-Relay-12V-30A-4-Pin-Normally-Open-Car-Bike-/252048082683?hash=item3aaf3c86fb:g:FswAAOSwMmBVwl5w

 

The drawing is in the thread I linked above dude

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