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buy me some race gas!
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Discussion Starter · #1 · (Edited)
okay. so i burnt up one fuel pump due to low voltage so needed to do this. i would highly suggest you do this with your fuel return system.

im going to try to explain this as best as i can and from what ive been told and learned.

the factory fuel pressure under load will drop because of the non existant fuel return setup. so the more boost you make the more the drop in fuel pressure you will have. by going to the fuel return system you dont lose fuel pressure. you gain it! so basically its opposite of stock. your fuel pressure actually rises. so basically whats happening is your putting a lot more stress on the fuel pump to work harder and whats really bad for it is voltage drop. thats what killed my fuel pump. under WOT its making that pump work super hard with not enough volts. so what i did was make a direct line from battery to help keep a constand volts.

The relay is just like a light switch. Anytime it receives 12 volts on pin 85, it will turn on the switch and make continuity between pin 86 and pin 87 on the relay. Being that pin 86 is wired straight to the battery this will send a nice, clean voltage straight to the battery with no other obstructions to the fuel pump. Once the car is shut off, pin 85 will lose its 12 volts causing the coil inside the relay to close and the light switch will then be turned off cutting the continuity between pins 86 and 87, which will then cut the voltage supply to the fuel pump.

heres the pics. i did not ground the fuel pump tho since the fuel pump is grounded through stock wirring.



The relay should have 4 pins on it. They are usually labeled 30, 85, 86, and 87
1. Wire pin 86 of the relay to the 12v supply wire from the stock ECU that you just cut. This 12v wire will now energize the relay to turn on. So now instead of the stock ecu energizing the fuel pump, it will energize this relay.

2. Wire pin 85 to a good ground on the car. Be sure it is a good clean ground, and use appropriately sized wire so you don’t burn up the relay. In fact you should be using appropriately sized wire for all of this.

3. Run a dedicated wire from your battery to pin 30 on the relay.

4. Run a wire from pin 87 to your factory wire that you cut that runs to the fuel pump.

this is everything i needed. cost me like 30 bucks for everything.


i used 14G wire to keep it semi close to stock wiring.

took the back seats out. remove 8 bolts for fuel cover.



after you need to pull the red wire with white stripe throught it. thats your factory power line



first i made the power wire coming from the battery. i put a 40A inline fuse in as well.



here the power wire put together. i solder the wires together by the way for a permanent hold.



cut the stock wire in half. put the a new wire here to this. the other side of this will go to the relay. this is the wire that will be power for fuel pump.



here it is all solder up.



here the wire all wrapped up. now if you look the left you can see the other red wire that is coming from the ecu to turn the fuel pump on. i did the same thing here with a new wire that will connect to relay.



i used a 4 prong 40a/14v relay. heres alll the wire connected with female connectors.



yes. i used the ground coming from the relay and mounted on seatbelt bolt. its a good ground. you can choose another if you like. i just stuck my relay in the corner here. i did wrap electrical tape around wires to keep them together and help clean it up.



after doing this. what a drastic difference in A/F since the pump now is able to keep up. so my fuel pressure was on 55psi and i was well below 10s A/F after so i had to lower my FP to 43.5 and im still in the mid 10's vrs before i did this i was in the high 11"s a/f. so this is a must for fuel return system as well.

big thanks to PRW for helping me throught this setup. pain in the ass but its well worth it now
 

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old guy
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So, is the 14 gauge wire larger than stock? It's been a while since I was under my rear seat.
If 14g is bigger than stock, then it's good.
 

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buy me some race gas!
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Discussion Starter · #3 ·
So, is the 14 gauge wire larger than stock? It's been a while since I was under my rear seat.
If 14g is bigger than stock, then it's good.
Yes 14g is a little bigger. 16g is what stock is.
 

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buy me some race gas!
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Discussion Starter · #5 ·
why did you sub? lol it does work and theres nothing i can really add to it. but i do suggest it if your doing fuel return line. my car fires up just like stock. no long start or hesitation. if you do the fuel return right it should start up normal.
 

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If I drop in a bigger fuel pump without a return line do you think I'll lose voltage and need this relay? Also, why are we losing voltage to the pump?
 

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It should be fine if your not doing a fpr..... But if you do a return system then do the relay !
 

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Cool. I'll bookmark it for down the road when I do the return line.
 

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buy me some race gas!
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Discussion Starter · #9 ·
If I drop in a bigger fuel pump without a return line do you think I'll lose voltage and need this relay? Also, why are we losing voltage to the pump?
if your staying stock setup then its fine.

by going to the fuel return system you dont lose fuel pressure. you gain it! so basically its opposite of stock. your fuel pressure actually rises. so basically whats happening is your putting a lot more stress on the fuel pump to work harder and whats really bad for it is voltage drop. thats what killed my fuel pump. under WOT its making that pump work super hard with not enough volts. so what i did was make a direct line from battery to help keep a constand volts.
 

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Good write up but it looks like you switched some numbers....86 should be 12V and 85 should be ground in step #1 and 2 if im reading it right.
 

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buy me some race gas!
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Discussion Starter · #11 ·
Good write up but it looks like you switched some numbers....86 should be 12V and 85 should be ground in step #1 and 2 if im reading it right.
good catch! those numbers are so hard to see sometimes lol. ill fix right away
 

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good catch! those numbers are so hard to see sometimes lol. ill fix right away
Np...ima have to do this really soon ive just been putting it off since my gen barely runs lol. i cant wait to get a tune already.
 

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buy me some race gas!
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Discussion Starter · #13 ·
Np...ima have to do this really soon ive just been putting it off since my gen barely runs lol. i cant wait to get a tune already.
it makes a huge difference on WOT with this fuel return. i couldnt believe it. just the a/f ratio change.
 

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Jedi Master
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MOre research on the topic.

If you look at say, DW, pump and then go to our car and measure voltage and apm it's drawing you'll see your not pulling 100% of what the battery generates, my guess is with the stock system, something gets lost in it.

so doign this on even a pump upgrade, i'd bet even on a stock pump stock fuel system, you'd get more out of it, might even have you running rich.
 

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buy me some race gas!
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Discussion Starter · #15 ·
MOre research on the topic.

If you look at say, DW, pump and then go to our car and measure voltage and apm it's drawing you'll see your not pulling 100% of what the battery generates, my guess is with the stock system, something gets lost in it.

so doign this on even a pump upgrade, i'd bet even on a stock pump stock fuel system, you'd get more out of it, might even have you running rich.
Yes! On stock setup with fuel return I was seeing super rich a/f. High 10 when turbo spooled but at top end it was so rich it stoped at 10 flat and woundlnt move because it was so rich. That's because u lose boost with stock turbo. I can't wait to see a/f with the tune I'm abou to run sice it was tuned on non fuel return. Bet I'm gunna run rich. But hey. Rather run a tad rich then lean. So more boost! Lol. I bet your can get over 400 Hp with stock pump and relay with fuel return
 

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Sweeeet... For the noobs, of course you'd have to tune timing to do this safely and get all the power you want!
 

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Interesting, but I wonder where the voltage drop happens. I'm an ASEE and this has me thinking. What's wrong with the factory fuel pump relay? Does voltage drop across it's contacts? Would swapping out THAT relay fix the problem? This just seems like putting a bandaid on the issue, albeit a solid bandaid, lol.
 

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buy me some race gas!
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Discussion Starter · #18 ·
Interesting, but I wonder where the voltage drop happens. I'm an ASEE and this has me thinking. What's wrong with the factory fuel pump relay? Does voltage drop across it's contacts? Would swapping out THAT relay fix the problem? This just seems like putting a bandaid on the issue, albeit a solid bandaid, lol.

the factory fuel pressure under load will drop because of the non existant fuel return setup. so the more boost you make the more the drop in fuel pressure you will have. by going to the fuel return system you dont lose fuel pressure. you gain it! so basically its opposite of stock. your fuel pressure actually rises. so basically whats happening is your putting a lot more stress on the fuel pump to work harder.
I don't know if you read this but because the pump is pumping more fuel its expected. the factory setup is expecting fuel pressure drop. not rise in fuel pressure. the pump has to work harder to keep the higher fuel pressure up. its not a bandaid. this keeps the voltage up when the pump is working harder.
 

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I don't know if you read this but because the pump is pumping more fuel its expected. the factory setup is expecting fuel pressure drop. not rise in fuel pressure. the pump has to work harder to keep the higher fuel pressure up. its not a bandaid. this keeps the voltage up when the pump is working harder.
I read all of it. It's this part:
this keeps the voltage up when the pump is working harder.
WHY does the voltage DROP is my question. What this is doing is putting a relay on a relay. Ok so the fuel pump is pumping more fuel with a return system. Still doesn't answer why the fuel pump is seeing a voltage drop. That's all :dunno:
 

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buy me some race gas!
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Discussion Starter · #20 ·
lets see if I can do it this way. the extra relay is there to turn on and off the extra power from the battery itself.

now take a bone stock car. bone stock. it has 55psi of fuel pressure. lets say the turbo is pushing 15lbs. the factory setup is 1:1 ratio as well. so when you reach your max boost your only seeing 40psi of fuel. the system was designed to see a pressure drop so it doesn't require as many voltage.

now take the same stock system. run a fuel return. start with 55psi. now add 15psi. your now at 70psi with 15lbs of boost. now the pump is pumping more fuel at WOT and at higher rpm. now the voltage must rise because the pump is working harder. not something the factory pump is use to seeing.

that's what I got out of it when learning. may not be right so if anybody has any corrections please tell me so I know and that way theres no mis information! I hate misinformation!
 
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