Wiring Questions For Intank Fuel Pump Upgrade

[ausdrift]

I am looking at fitting a universal fuel pump, eg walbro 255 to my R33 and I had a couple of questions on the wiring of it.

1, This may be a bit stupid, but from pics etc it seems like the wires and terminals are directly submerged in the tank with the fuel. How does this not ignite or pose an explosion risk?

2, I read that its a good idea to hook up a relay to get the juice from the battery direct. Its been about 10 years since I last did one of there, does anyone have a tutorial/diagram/link to video etc that explains it and what to use (or can you tell me now)?

Thanks all

[Hadouken]

Yes

[kingtube69]

Hi mate,

link below

http://www.sau.com.au/forums/topic/234796-re-wiring-your-fuel-pump/page-2

Should help - I'm about to do mine this weekend.

[Ben C34]

Full knows to not explode in the tank. It's not stupid

[89CAL]

Do you see sparks coming out everywhere when you flick switches?

Wires are fine as long as the insulation between them is fine.

I believe there may be types of wire that are suitable to use in fuel but i have never looked into it so not sure what sort

Remember that for a fire to start it needs an ignition point. Electricity does not provide an ignition point unless it suddenly becomes able to create a circuit between a gap. Think of how ignitors (think bbq lighters) and even spark plugs work.

This probably isnt a very good explaination

[Dose Pipe Sutututu]

mixture is too rich to ignite, not enough oxygen

even if you arc power wires inside a fuel tank it still won't ignite

[KiwiRS4T]

mixture is too rich to ignite, not enough oxygen

even if you arc power wires inside a fuel tank it still won't ignite

but don't try this at home!!

[kingtube69]

This is what I am using today - From Cal in an old post from a few years back. Looks simple to follow and I've done most of it in under 30 minutes. I need to change the pump so I'm procrastinating about changing the pump and finishing the wiring.

[Dose Pipe Sutututu]

if you're using a Walbro 255, there's not real need to hook up a fancy relay.. just bypass the FPCM by earth the fuel pump wire from the top connector of the fuel tank cover.

at 100psi load (which you won't ever hit) it only draws a theoretic max of 14amps @ 13.5v.. this would mean you're running 50psi of boost through the motor to achieve nearly 100psi fuel pressure....

Let's use real world numbers, your base fuel pressure is 3 bar, i.e. 43.5psi.. and you put another 1.5bar ~22psi through your motor.. that means you're only loading up the fuel system to 65psi or so...

Soooooo... that means using a Walbro 255 you're only drawing about 10.5 amps at full noise...

food for thought

[kingtube69]

if you're using a Walbro 255, there's not real need to hook up a fancy relay.. just bypass the FPCM by earth the fuel pump wire from the top connector of the fuel tank cover.

at 100psi load (which you won't ever hit) it only draws a theoretic max of 14amps @ 13.5v.. this would mean you're running 50psi of boost through the motor to achieve nearly 100psi fuel pressure....

Let's use real world numbers, your base fuel pressure is 3 bar, i.e. 43.5psi.. and you put another 1.5bar ~22psi through your motor.. that means you're only loading up the fuel system to 65psi or so...

Soooooo... that means using a Walbro 255 you're only drawing about 10.5 amps at full noise...

food for thought

I never knew about this! It would have been so much easier to do this. I got a Walbro 400 E85 pump so I thought it necessary to do this.

Is it still fine to do it either way?

[Dose Pipe Sutututu]

you should hard wire the E85 pump, they drain loads of current!

I've gone full boofhead on mine and have run 12ga wire to the fuel lid and to a 40 amp relay with a 30 amp fuse

[kingtube69]

Hmm, What you did is pretty much what I did.

My thoughts were this though (tell me if I'm understanding it wrong) Walbro would have never run such thin wire to the pump itself if they thought it would be a massive problem or that it couldn't handle it. Hell, they have 16 gauge from the pump to the plug it comes with. I have read at full tilt on E85 the pump will draw 19A (not sure if thats correct though). I selected 25A automotive power wire, relay and a 30A fuse.

[breaker1845]

If you read the specs you can determine how much you will be running at full load roughly. In general those bigger pumps draw much more current and if you are hard wiring you should use some thicker wire and an in-line fuse for safety measures. I've seen cases with the 460 pump drawing large amounts of current and burning through the stock wiring/fuel tank hat almost causing a fire.

Realistically the pump will draw as much current as it needs/wants for the given scenario and if the wire can't handle the current going through it you'll find out about it. Having said that it can be rare for it to happen and if you aren't pushing a fuel pump that hard then you probably won't ever experience that potential scenario. Better to be safe than sorry.

[scotty nm35]

Further to this, even the relay won't last long with a Walbro 460L, I have seen many drawing over 30 amps, blowing fuses and melting relays and tank lids. The issue isn't the pump, or the wiring. I suspect the relays don't get enough voltage to pull in the contacts hard, hence the current spikes as the voltage drops due to the bad relay contacts. Some last days, some months.

A solid state relay would fix it, but you lose 0.7V over the output switch. Probably best to run a solid state relay to power the coil of the 70 amp power relay, that way you can be sure the 70 amp relay is getting the full 13V it requires to energise properly, without affecting it's ecu controlled operation.

[kingtube69]

Jesus - I didn't think it was that bad.

Guess I may have to go this route.

Scotty, what are most people currently doing with their bigger pumps? The solid state relay or bypassing the ECU operation all together?

[ausdrift]

right.

And with soldering the pump wires together for in the tank, I assume you would need chemical proof heat shrink or similar. Anyone know where to get this?

[Dose Pipe Sutututu]

right.

And with soldering the pump wires together for in the tank, I assume you would need chemical proof heat shrink or similar. Anyone know where to get this?

I personally have use chemical proof heat shrinks, however when they loosen up with age your wires end up being exposed...

Better to use crimps, then slide the hard cover off.. heat up the metal, fill with solder and slide the cover back on.

DO NOT BYPASS THE ECU, you need the trigger from the ECU that goes into the OEM fuel pump relay... if you bypass the ECU and your motor stalls, the fuel pump will keep pumping... in the event of an emergency you don't want that especially when fuel leaks are involved and heat.

[kingtube69]

I personally have use chemical proof heat shrinks, however when they loosen up with age your wires end up being exposed...

Better to use crimps, then slide the hard cover off.. heat up the metal, fill with solder and slide the cover back on.

DO NOT BYPASS THE ECU, you need the trigger from the ECU that goes into the OEM fuel pump relay... if you bypass the ECU and your motor stalls, the fuel pump will keep pumping... in the event of an emergency you don't want that especially when fuel leaks are involved and heat.

Thank you for the info Johnny,

I'll see how mine goes but I believe I'll go the solid state relay unless there is some other way I should do it.

[kingtube69]

If I'm understanding correctly it should look like this

The idea is that the voltage coming from the standard wiring is significantly less than the voltage needed to keep the SPST/SPDT relay closed under load and that a solid state being a relay because it doesnt use a magnetic coil to close the circuit and copes better with small voltage levels making it suitable to use as a relay to charge the SPST/SPDT relay.

Correct me if I'm wrong unless there is a better way to do this all

[Dose Pipe Sutututu]

I think you've got the wrong idea...

SSR takes the trigger from the same trigger wire that comes out of the ECU to the relay at the back of the car.... do not use the output of the OEM relay to trigger your SSR because of the OEM relay dies you're f'd.