Fuel pump wiring advice

[Mk4Gaz]

As the title please guys, I'm about to fit my walbro 450lph pump for my single build, but want to ask how everyone wires their pumps up?

 

I fitted a 255lph in place of the factory one, a few months ago, but used the stock wiring setup for it.

 

With the bigger pump, do I need to upgrade anything?

 

I was considering the 12v mod, to bypass the stock ecu, but that would mean the pump would run every time the ignition was switched on - no major biggie, but it seems like a bodge to me.

 

I then thought about wiring a relay in, via a new feed pulled from the battery, and connected to a switched live. But again, the pump will run every time the ignition is switched on.

 

Any other options?

[jagman]

New fused feed from battery to relay , relay to pump ( use quality wire) , relay switched from ECU feed that went to the fuel pump control unit . Use high current relay .

Now the ECU controls the pump and shuts it off in an accident , it also runs pump for a couple of seconds on engine shut down to keep lines primed .

-Option to use a circuit breaker in place of a fuse , so you can reset if you have problem and not be stranded with a blown fuse ( you never have a spare fuse , no matter how many you leave in the glovebox )

[Mk4Gaz]

Thanks for the reply bud

 

Pretty much what I was planning to do, I bought some 20a wire and a 30a 4 pin relay for the job.

 

I've already pulled a battery feed into the boot. The main thing I need to know, is what colour wire to use as the switched feed for the relay?

 

Digging around on the Internet suggests a blue with red trace at the fuel pump ecu.

 

There's two power feeds at the ecu, blue/red and blue/orange by all accounts. One is an - ig live, and one is the 9v - 12v live, that makes the pump run high or low speed.

 

What I didn't want to do, is use the wrong wire to switch my new relay.

[mellonman]

http://www.mkiv.co.uk/vbb/showthread.php?272714-12v-mod-will-this-work

[Mk4Gaz]

Cheers dude, that's pretty much what I found last night whilst searching.

The only thing I couldn't find a definitive answer for, was what wire to pull from the stock fuel pump ecu, to trigger the relay.

[markssupra]

Its one of the thinner wires to switch the relay iirc. I've done this for the twin pumps so should know but cant remember:blink:

 

I know its either pin 21 or 22 on stock ecu.

[Mk4Gaz]

All done and working now, should've updated this but forgot!

 

I used the ecu side of the blue/red cable as the relay trigger, and the other side of that cable to send the battery voltage to the pump. It's the stock supply wire that normally feeds the pump, however it now carries the full battery voltage all the time, rather than the ecu varying the voltage.

[Mk4Gaz]

[jagman]

I did give the answer , but you seem to have not followed it - lol

1 fuse ratings are a multiple of the constant expected current , this is because of start currents can run higher

2 your current will be around 21 amps at full load

3 new cable is a single cable run and is better for heat ( loomed cables have reduced capacity)

4 quality cable is used as it has much better tolerance for overheat and fire resistance , a short circuit with cheap plastic insulation (read halfords cable) with melt and catch fire almost instantly

5 check the current max on those crimps you have used

6 supply cables drop voltage , more the longer the cable , so thicker cable is used - here the quality of cable counts - thick poor insulation tricks you into thinking the current capacity of the cable is much higher than it really is

7 using old original cable and forcing it to carry new / altered electrical loads can highlight any problems with chaffing or cable run

 

So how do you know what quality cable looks like ?

Some easy tips are , cheap cable is always plain copper conductors , this limits their ability to cope with heat , quality cable is tinned copper , or silver or nickel plated copper conductors .

Cheap cable is plastic insulated , quality cable is usually a vinyl coating - it feels slippery in your fingers

Lastly use a fag lighter on the cable , a sample piece obviously , cheap cable melts and catches fire in a few seconds , quality cable remains intact for several minutes and won't melt .- despite having thinner insulation

Sorry for lecture , but people simply don't know and many expensive project cars are done using awful cable and the cost of quality cables is not that expensive

Lastly for example a thin gauge quality cable around standard car size will run 75 amps for 5 mins without major melt down and fire - this gives you time to jump out and disconnect the battery - thus saving your pride and joy

[Mk4Gaz]

Ok, so here's how I've done it.

 

I already have a 4awg cable running from the battery to the boot. Fused at the battery, with a 40a fuse.

 

I have a distribution block in the boot, from which I've run a 20a rated cable, to a 30a 4 pin relay.

 

The blue/red cable from the fuel pump ecu to the pump is the stock supply wire, which carries 9 or 12v depending on what the ecu says.

 

I've used that cable to trigger the relay

 

The other side of that wire, goes to the fuel pump plug, which supplies the pump with the +ve feed. That wire now goes from the relay, to the stock plug - but carrying the full battery voltage from the relay.

 

I've put a 20a fuse on the supply to the relay, with 20a rated cable.

 

According to the walbro instructions, the pump will run at about 14a at 12v, and 16a at 14v, so I'm quite sure the cable will be ok. The crimps I've used are blue, and are rated at 15a, I guess I could change those to yellow as they're rated higher?

 

I thought I had followed what you'd said, albeit I've used the stock wire to feed the pump, rather than run a new cable from the relay to pump. I wasn't sure how I could get a new +ve feed to the pump itself, with the plug on top?

 

Also, the wiring I've used, is much thicker than the wires actually on the pump itself, which is pre wired at the factory. Not just the insulation, but the amount of strands that make the cables thickness up.