need pro's and cons of doing this... have been told that the skyline ECU changes the power of the fuel pump from 5volts at idle to 12v when revved?? is that true? i can hear the sound of the fuel pump change when reved, but it won't idle also, how do i go about wiring it straight to the battery through a switch? what wire would i use? what fuse? can i just take a power feed from the fuse box, send to switch then onto fuel pump, then earth the other wire? anything i've missed cheers si
You can power it from the battery use a 10A fuse off the battery then to the switch to the pump. If you also want an idle setting you can have another switch but put a resistor in line with it to reduce the voltage to the pump
So would I. Its not variable speed on mine but I rewired it ages ago with some 16AWG cable running from a distribution fuse block left over from my ICE days (with 4AWG cable to the battery), running to a relay using the original pump feed wire as the switching signal. Voltage at the pump went from 11.5 to 14v.More V = more flow.
so the relay is instead of a manual switch? so it is as simple as wiring a switch in, with an inline fuse
Si if you want ring me and I'll talk you through wirng it up or msn I can send you diagrams to do it either of the ways PM me if you want more help
I'd do what Steve says. Run a new wire from the battery to the pump via a relay, then use the original fuel pump wire to turn the relay on. Don't be scared by using a relay, it's very simple once you know where to wire the 4 pins.
just sounds a bit advanced for me, also wondered how i know which wire is + and which is - will it make any difference doing it anyway? is it right about the changing voltage on idle? si
It's easy once you get your head round it Si A multimeter will be handy so you can figure out which is + and - I know the GTR pumps have a 2 stage voltage thing, but I presume it's ECU based rather than pump based which is why a GTR pump sounds loud in an S-body, cos it gets full voltage all the time. Either way, getting a good feed direct from the battery and using the stock + wire to trigger the relay will give a guaranteed good strong power feed that is still ECU controlled for priming and such
i've put in a switched relay to my fuelpump. it sounds hard, but when you get enough info, it's dead easy. use what's called an "87 relay" it's a 4-prong relay. like this one {} connect like you see the bottom part of the picture, can't go wrong. and this is coming from an electrical retard. if you look at my buildthread, you'll see all the wiring i've done. about 90% of the car, and that's just because somebody told me how to do it. it's really easy actually
Yeah the dual pressure thing is ECU controlled as I've looked at it for the VEMS RB25 harness adaptor, I was told by a highly respected Skyline tuning company to not bother trying to control it because they often don't work, and the cars run fine without them. I think its there to lower fuel pressure for low RPM emissions purposes (less fuel pressure = longer injector opening times which means more control resolution). You should be able to use the standard fuel relay control wire, to pin 86 on James' diagram.
The OEM feed goes direct to the fuel pump, then the ground wire goes through the FPCM (Fuel Pressure Control Module) which either switches to ground (giving full voltage), or through a dropping resistor (giving the voltage drop).
Why do you lose voltage throught the FPCM then when its directly connected to ground? as the post above where its mentioned you get a 14v feed when connected directly. I'm just trying to understand the ins and outs and why you actually benefit from it. Surely you should get the same feed voltage with the new setup?
I'll try and add clarity to my previous post: The FPCM switches the pump's ground either directly to ground - or to ground via a "dropping" resistor. If it goes directly to ground you get full power, if it grounds through the "dropping" resistor you get less. The problem peole have found with voltage drop is that the stock wire causes too much of a voltage drop so they 'hardwire' a cable with a higher current rating and use a new relay while they're at it.
