Fuel Pump Control Module & Dropping Resistor

[J_Red33]

Hi everyone, I've reacently read up on different issues with stalling & so on & believe I've stumbled across my problem being to do with the fuel pump control module (or FPCM) or the dropping resistor that's also in the circuit.

But what I want to know, so I don't have to go pulling my amp out & stuff for nothing (went to do it today, it's gonna be a moungrel) is where are these components located? I want to actually fix this problem properly as opposed to just doing the old earth the pump wire. Once I've established it's location I plan on coming up with a mod to prevent the stall on take off issue that it causes, so if anyone can tell me & maybe provide pics it will be much appreciated.

Cheers

[J_Red33]

Well since no one else seems to have found these components I finally took it upon myself today to find them. The first photo you see is of the back right corner of the cabin. The fuel pump control module is located in the U shaped bracket underneath the parcel shelf:

This is a closer shot of it. Though you can't see it in this pic, it has a 4 wire connectio. Earth (Black), Power(Light blue), Pump negative (Grey) & control (Orange) wires.

What wasn't immediately apparent however was that there were in fact 2 grey wires with the same marking coming from the fuel pump. These did turn out to be commonly connected. The second wire was traced around till I ended up on the passenger side of the boot (having pulled all the boot trim out) where the ballast resistor is located.

This was bolted in above the car jack mounting bracket. You can see the ring mark on the hole it was bolted in on.

What I found while I had all of this exposed was that the wiring to & from the dropping resistor is not good enough, with voltage drops across the wiring going to & from the resistor. The wiring for the dropping resistor is actually thinner than the FPCM, & why Nissan shortchanged on such an important piece of wiring I don' t know.

I will now have to think about all the stuff I'll need for a proper fix to this, will post it up once I've got it soughted.

[rbscreamer]

Hey Buddy, I know its a little late from 2006. Thanks for the above information. I have a r33 series 2 turbo. My cars getting resprayed at the painters. Car was working fine the day before. Than today, owner of shop said that car is starting and dies after a min of running and would not start. Call the auto electrcian and he said that there was no earth going to pump. I thought what the hell. Earth would not just disappear in a day. I am trying to find out where does the fuel pump get its earth from. I know it starts from the fuel pump but I am trying to trace it till where it gets its earth. Can u help me Bro. I am going to check the fuel pump module and ballast resistor. I think the painters must have undid somthing when they strip the car for paint. Cheers.

PS I am like u. I want to fix the problem and not just do the direct earth to fuel pump.

[J_Red33]

Hey as per my email:

Hi there,

Yeah it was a long time ago. I had to remind myself what thread you were on about.

Luckily for you I know just what you're looking for.

The earth for all the fuel pump wiring is an eyelet that has 4 black wires going to it, 2 are for the pump. This is located on the panels behind the back seat towards the right hand side.

The seat is a bit of a bugger to get out if you haven't already, though I assume you have if you know where the control module is.

Seems a little odd that it will run for a while & then die.

Just looking at the circuit diagram though earth is via the ballast resistor & the control module. So the only way the pump is going to have a full earth is with the control module active while the engine is running. Or you could do what I did & bridge the pins on the connector.

If you're just checking with a meter, measure resistance, not continuity as that only measures a few ohms. Possibly the trap that the stupid sparky fell for (there's a lot of them that don't know much).

Let me know how you go. Hope that helps

Just to add to this if you look at my first photo from my old post the earth wires are on the eyelet bolted just under the white box in the centre of the picture.

You can see they come off the main loom.

[BH_SLO32]

It sounds like the painters have disconnected the dropping resistor when accessing the aerial. With it disconnected the FPCM will allow the pump to run for a short period before the ECU switches it off and if the dropping resistor is not connected the pump is open circuited.

Cheers

[rbscreamer]

It sounds like the painters have disconnected the dropping resistor when accessing the aerial. With it disconnected the FPCM will allow the pump to run for a short period before the ECU switches it off and if the dropping resistor is not connected the pump is open circuited.

Cheers

Thanks Bro, thats what happened. The stupid spray painter disconnected the aerial and removed the resistor when he was wet sanding the car. I even paid $25 bucks for a auto electrcian to fix it. He found no earth to the fuel pump so he tap earth from another source. I had to repair the earth wire he cut. But thanks to J_Red33 topic. He has shown me where to look. So I say thanks again to J_Red33. (^_^)

[discopotato03]

A big thanks to J_Red33 for showing me where the fuel pump resistor lives in a GTS25T , I would have found it eventually but you showed us where to look .

Man they go around that boot and rear fire wall looking for places to hang the fuel pump control system , I suppose the resistor needed to be away from the fuel tank filler for crash / fire reasons .

I'll be curious to see how hot it gets cheers A .

[discopotato03]

I ended up in the back of my GTS25T yesterday chasing the standard fuel pump wiring so I know where it all goes . The upper rear seat was already out and I removed the firewall access panel as well .

It goes like this in a 96 S2 .

The fuel pump relay switches power to the pump via a light blue wire with silver bands . It runs into a common loom with the large power feed wires ie White , White with red trace , and red which feed the fuse block under the parcel shelf in the boot .

This loom runs behind the top of that access panel hole on the boot side and is taped up inside a split black plastic insulating tube from near side to off side . It then runs into a tall shallow white plastic insulator gadget that the access panel overlaps . I opened up the white gadget and found three light blue wires with silver bands so I then opened up the above mentioned loom to confirm that the single wire had branched into the three inside the black plastic insulator tube . I taped it back up with the fuel pump wiring separate from the large power feeds .

Now those three light blue wires , the first runs into the boot and down the loom until it branches towards the fuel tank lid - pump power feed .

The second runs down the inside of the firewall in the main body harness heading towards the front of the car on the drivers side . I believe this goes to the air regulator under the inlet manifold that heats up when the engine warms up .

The last light blue wire runs up the inside of the firewall to the top RHS corner and back into the FPCM .

I then started to follow the pale grey wire from the pumps loom back towards the boot side of the firewall and to the inside at that white rectangular gadget . Inside there is a pair of pale grey wires and if you trace them back towards the pumps loom they both join under the insulation in the boot .

Actually where they are joined the second wire is noticeably smaller and they run inside and up the firewall where the thicker one heads back to the FPCMs plug . The thin one goes back into the boot and into the loom that runs across the back of the boot under the trim . I'm 99% sure this reappears at the loom side of the dropping resistors plug .

Now for the body earth/grounds . As mentioned in an above post there is a bolt into the rear firewall with two brass eye terminals and from memory five or six black wires running to the drivers side and back into the main body loom . There is a black wire at the FPCMs plug and it runs back to this earthing point . In roughly the same area as the above mentioned thin pale grey wire heads back to the boot and a thin black one appears and runs to this body earth terminal/bolt . Again I'm 99% sure this is the earth return from the dropping resistor .

So the system must work like this .

ECU switches on the fuel pump relay which powers up the pump , the cold air bypass reg , the FPCM .

The earth return from the pump is permanently connected to the dropping resistor via the thin pale grey wire , after the resistor the circuit is connected to ground via the thin black wire .

Off idle the ECU sends a signal to the fourth wire on the FPCMs plug switching its fancy electronic switch to basically connect the pale grey wire to the black one earthing the pump and bypassing the resistor .

Now the OP mentions below his third pic , of the resistor , than Nissan used quite thin wire to and from the resistor which concerned him .

If you think about it at idle inlet manifold pressure is low (in relation to atmospheric) so the vacuum signal to the FPR will also be and the load on the pump at low pressure will be low . The current draw from the pump would be low so Nissan obviously thought light wiring was all they needed .

Off idle the FPCM uses the slightly larger pale grey pump earth return wire and the larger black earth return wire to ground .

Now if you choose to use heavier wire it's easy to replace the section between the relay and the fuel tank cover though I'd still have power to the other pale blue wires .

It's also reasonably easy to use heavier wire between the pumps earth return (pale grey) and the FPCMs plug . Ditto for the black wire from that plug to chassis ground .

Once you know where the dropping resistor is it's simple enough to replace the thin black lom plugs wire with a heavier one to earth and the pale grey one back to the fuel tanks cover/plug .

There's really only two questions now , can we buy the terminals for the Nissan plugs which all look the same BTW .

And can the FPCM handle the higher current draw of larger aftermarket pumps .

A .

Edited September 1, 2013 by discopotato03

[Dose Pipe Sutututu]

THE FPCM can handle it, however not with massive walbro 460L pumps, this is where you need to be smart and use the output of the FPCM to trigger an external relay and run your own dropping resistor.

I've used the stock resistor, however it's not capable of dissipating enough energy. I've ordered a new 0.3 ohm 50 watt resistor to replace the one in my circuit:

http://www.skylinesaustralia.com/forums/topic/430312-r33-fuel-pump-wiring-better-feed-retaining-fpcm/page-2#entry7163251

[SmashBoxx]

Hey guys.
I know it's a hella old thread but this is the closest I've seen to my problem.

Hit a dirt embankment with the drivers side rear of the car, enough force to bend LCA and knuckle.

The car now runs initially for a second after a prime but then shut off.

If I prime it a few times before cranking, it runs for a couple seconds then cuts off.

The car has fuel pressure to rail just fine.
I swapped the FPCM and the resistor module but no good.

Any ideas?

[89CAL]

As an FYI for this thread, here is the Fuel pump control wiring circuit:

[Dragondan25]

I know this is an ancient thread but it was helpful with my issue blowing fuel pump fuses. I had replaced my pump which had seized up but when I tested it the fuse blew straight away. Did some testing with multi meter and following the wiring diagram.

Ended up being the FPCM having an internal short causing it. Fuel pump and fuses worked happily with the FPCM unplugged, even took it for drive. Got another FPCM and tested the pins to confirm not shorted, plugged it in and it is working fine.

[GTSBoy]

32 minutes ago, Dragondan25 said:

Got another FPCM and tested the pins to confirm not shorted, plugged it in and it is working fine.

Time to plan to bypass that, because it's probably only a matter of time 'til the new one dies too.

[Dose Pipe Sutututu]

being a R33, just bridge / delete the resistor pack next to the power antenna, done.

[EndZee]

Guys since i bought r33 gts25t coupe 1994 automatic a/t(manual swap 350z gearbox)  all i got is problems, always problems. Lets start with that when i turn key into ignition(ON) fuel pump doesnt always works. Sometimes i have to turn key twice Off/on/off/on until it primes. Its new, dw300 - 340lph. My gearbox broke so i did gearbox swap, install different intake manifold, injectors and i take pipes. Car was sitting in garage for more than half a year. I did assembly all not that long ago and when i turn ignition cant hear prime. All of sudden it stopped working. Theres many videos on YouTube how to make relay mod on r33 straight from battery so i did and it doesnt work! 😰

30 - battery positive 
87 - positive from fuel pump to relay

85, 86 - one of two wires from original fuel pump wires(light blue, grey)

and it didn’t work.

so I check on ignition and took original BLUE relays wires from trunk, next to fuses. (I believe it’s IGN+ and ECU pin 18.

it didn’t work… 

tried connecting (IGN+ from og relay) and (ECU 104 from 1of4 FPCM wires) to my new relay 85/86 and it didn’t work. 
I unplug FPCM. Didn’t work.

im thinking what’s wrong

 

fuel pump is working, if I leave IGN+ on 85 and 86 straight to ground it works but it’s just nonstop. Since it getting constant 12v after key in ON.

light blue wire gives me 6-8v. 

so how this should be connected? What causing ECU not giving — on pin? Or I did sth wrong and that’s why it doesn’t work?

I need negative signal on ECU that control fuel pump. What this should be?

[GTSBoy]

Have you got the wiring diagram?