Thread: Fuel pump problem

Having an issue with my fuel pump.

I have it hardwired as follows:
The original thin + and - wires that usually power up the pump, are now switching on the aftermarket relay, which then gives 12v+ to the fuel pump, while the ground on the fuel pump is now taken straight form the battery negative terminal.

The problem:
When I turn on the ignition, the fuel pump primes and gives 3.7bar pressure, as set with the afpr. But then after the pump stops priming, the pressure drops back down to 0 quikly. Also, while cranking the AFPR gauge is not registering any fuel pressure.

When I give the new fuel pump hardwire relay constant 12v+ then the fuel pressure stays at 3.7bar while cranking. But when I use the OEM fuel pump wiring to switch on the relay it drops off and doesn't pump on cranking as explained above.

Now, I'm busy fitting full management, and non of the original distributor wires are used. So I'm wondering if the ECU perhpas doesn't know that the motor is cranking over, and therefore somehow it's not supplying further power to the fuel pump wires? Any ideas?

Also, if I leave the ignition in the ac position, the ECU starts making this buzzing sound. Like the green relay on top of it is switching a 1000times a minute. If I turn the ingiton to "on" it stops.

No one??

At least tell me if the fuel pressure is supposed to hold steady after the pump primes...

my setup always held steady after it primed. I was set at 4 bar and never had problems with it holding. I had a Megan racing fpr on my last setup that didn't hold pressure at all once the car was off however. I don't think that the distributor gives any feedback to the ecu as to whether or not the car is cranking vs. sending fuel. At least I've never heard of that. Miko might know, but I'm not that great with this ecu either.

Sorry to say I have no idea on the relay on the ECU, almost sounds like the relay is dying. In one of my old CRX's I had a relay that started doing that right before it died.

i know this is off topic. are you putting the 60-2 pick up in the dizzy?

oh yeah i agree bout the relay thing. when it does that its about to die

Is it a problem if the FPR doesn't hold the pressure? I think to avoid any possibility of an issue I'm going to power up the fuel pump whenever the ignition is in the "on" and "start" positions. So it won't prime by itself, but I can prime it manually by holding it in "on" for a second or two before switching on the car. (what's the purpose of priming anyways?)

I'm using the VE dizzy, which is wired directly to the management system's outputs.

As for the relay. It's one of those OEM nissan jobbies that sits on the ECU. I suspect it powers the ECU? If that goes I'll probably have to get a new one from the agents. - crap!

I'm using a combination of the management system and the ecu at this point. The ECU to regulate and power the radiator fans, and the EMS to manage the Ingition, fuel, tps etc. If I do wire the fuel pump relay directly to another ignition power source, then I'm actually thinking of ditching the OEM ECU entirely if I can get the radiator fans to run on their own independant circuit.

Can't think of anything else the ECU controls that won't be taken care of with the EMS?

Found this on another site:

A computer-controlled relay is the most common method of controlling the pump. The computer looks for an rpm signal to decide if the engine is running. If it sees the proper signal, it grounds the relay, and, in turn, powers the pump.

So it seems my ECU won't power the fuel pump when cranking if the ECU isn't getting the distributor signals.

here's the full article:Prime your skills to tackle electric fuel pump trouble - Building & Home Products, Automotive, professional tool and equipment news, professional tool information, professional tool info, professional tool news, professional tool magazine, profession

I would suspect that the relay has something to do with this issue. You are going standalone anyway why not just take out the OEM ECU and make the Standalone control the fans? Or does it not do that? I am sure you could find something that would turn on the fans at a certain temp.