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Should I remove the fuel pump ECU?


Scott

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I've got a few queries regarding wiring up my fuel pump. I'm currently running a stand alone ECU (Syvecs) which outputs to the fuel pump ECU to turn the fuel on.

 

With this in mind, am I right in thinking that the fuel pump will be in 12v mode all the time? If not, what is it that controls the 9v/12v switching?

 

What wiring should I be switching out? I guess 12awg is plenty for most setups? I'm only running a single Walbro 450 pump so I would imagine that would be plenty? If I was to upgrade and run 2 pumps the second would have its own 12awg feed anyway.

 

What is overkill and what is worthwile? Should I just make a completely standalone system from the battery/ecu to the pump with my own relay etc, or is some of the wiring in the system useful?

 

There's an AWFUL lot of sketchy information around, with varying opinions on what way to go. I'd love to hear what people run in their cars and what sort of power you guys are running.

 

Ideally, if the fuel pump ECU worked, I'd like to leave everything in place and just beef up the wiring from the fuel pump ECU. I only want to do this job once though so I want to make sure I'm going the right way about it.

 

Thanks

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Just thinking out loud (voltage drop). I have a 0 gauge cable running from the fusebox to my boot for my various amps. I'm using a block to split the 0 gauge for the amps, I'm thinking it would be beneficial to use one of the take offs from the block in order to power the fuel pump given the size of the core. Any issues with this?

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The fuel pump ecu controls the 9/12 v switching . With my walbro 400 I had to bypass the stock fuel ecu 9v as there was just not enough power to run my pump. So done a 12v mod using a relay so in the event of a crash the ecu will still cut power.

Wiring straight to a live 12v in the boot that is not controlled by the ecu maybe a bad idea if you get into a crash and go up in flames.

Search 12 volt mod I done a drawing how to wire in the relay that's been used many times now

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Would that not mean that you're using a 9v signal to actuate a 12v relay? Is that not a little risky?

 

BTW I didn't mean just to feed 12v directly to the pump, I meant use the 12v via a relay to power the pump. Give me some credit ;)

 

Also, are you sure your information is correct in regards to what sends the 9v signal? This guide.....

 

http://mkiv.com/techarticles/12v_mod/12v_mod.htm

 

Suggests that it's a signal from the std ecu that tells the fuel ECU to switch between low power and high power. Does the Syvecs still retain this function? (Or any other ECU for that matter).

 

It's this sort of information I'm trying to weed out as there's so many people with so many opinions on how it works.

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One will be the correct answer, the others will have old wives trying to convince you that their wrong is right. :)

 

I'm thinking it may be a lot of he said/she said kinda thing without anything actually being tested properly.

 

My query comes as I've read a lot about people using the stock wiring to activate a relay, then using a 12v source to power the pump directly. That all sounds fine but there's surely an error in that. There's a 12v "in" to the fuel pump ECU and a 9/12v "out" from the ECU which goes to the pump. The 12v "mod" bypasses the ECU by connecting the 12v "in" and the 9/12v "out" making it a 12v constant. If you use the 12v "in" for your new relay circuit you're as well taking out the fuel pump ecu altogether, it's not being used at all. If you're using the 9v/12v "out" there's a danger that the 9v may not activate the relay or may drop at any point causing real issues, additionally I don't get how this benefits the system.

 

The Syvecs has a fuel pump 5v trigger onto a 12v relay (I guess). This then activates the fuel ECU/relay/whatever and allows the fuel pump to run. I'm thinking I can just connect this "out" directly to a high amp relay in the boot to control the fuel pump with a heavy duty 12v line.

 

I don't

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I ran my relay signal wire from the output of tge stock fuel ecu. Initially i tried it by using the ECU - fuel ecu signal wire, but it meant the fuel pump was running whenever the key was inserted.

 

So you are running your relay off of 9v until 4krpm? That doesn't sound safe to me.

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http://www.supraforums.com.au/forum/topic/27751-new-and-improved-12v-fuel-pump-mod/

 

Just going through the above just now. Good to see multimeters so will see what's said :)

 

They've gone with the same as you guys. It doesn't sit right with me at all but I guess the range on the relay selected is what matters?

Edited by Scott (see edit history)
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Any reason for ditching the ECU mate? I don't know if you have any other fuel prevention but the fuel ECU will cut the pump if the engine shuts down, having it a switched relay without the ecu won't. It's the main reason I want to keep the ECU in place but use a low enough pull up relay to make sure there are no issues with it dropping out

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I've gone with the following relay....

 

http://www.ebay.co.uk/itm/ON-OFF-Heavy-Duty-4-Pins-40A-40-Amp-12V-Relay-12-Volt-Top-Car-Bike-Automotive-/161886771221?_trksid=p2141725.m3641.l6368

 

The main reason is the drop off voltage which is 1.2vdc. This means that the relay will stay enegrised till the voltage drops below 1.2v which will only happen with a serious problem. I'm happy enough to go along with that so I'm definitely going to be following the majority method from this thread.

 

For anyone wanting to follow in my/our shoes, just make sure that the relay you use has a LOW drop off voltage. As long as it does, you'll never need to worry about the 9v "low power" standard.

Edited by Scott (see edit history)
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Think I'll go for that too, just to be on the safe side :) Cheers mate. (although I hid my relay behind the passenger rear quarter card :cry: )

 

Ooooo ouch. That's probably one of the worst places I've ever accessed on the supra (changing rear speakers). Mine will be going in with the fuel pump ECU :D

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Been running my 12v relay on 9v feed for 4 years now pritty sure its fine ;)

 

You say that, but it's not a good idea to give advice to do something when you don't fully understand it. Let me put it to you this way, if I had followed your advice blindly without looking into it and used a 9v drop out relay instead of a low v drop out relay I could blow my engine. The fact is, you've been lucky with your relay selection. Other people might not have been so lucky.

 

Now that I've investigated it fully I'm happy to accept that your method is indeed fine...... as long as a suitable relay is used in the circuit.

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