R33 Gtr Fuel Pump Issues

[r33gtrv-spec]

Hey,

After countless hours of reading about similar problems with -ve voltage regarding the fuel pump I've decided that I'll have to put my problem to you guys to hopefully help me out.

The car has been in a security and audio workshop for the past few days getting a new system put in. As we were going through the new additions to the vehicle, starting the engine via remote start, running it, stopping it etc.. It all of a sudden died. Tried starting it again, no luck. It sounded like it was a fuel pump issue as the fuel pump stopped priming, but being so late we decided to work on it again come Saturday morning.

Next day the same problem occured. We managed to start it for a minute but again it just died. After speaking with a mechanic and doing a fair bit of research we were under the assumption that it must be fuel pump related. We began by swapping the dropping resistor from another GTR. No luck. We ended up pulling the whole new alarm system out to make sure it wasn't related. No luck either.

We directly earthed the pump to ground and presto. She started up and ran, albeit rich, she stayed running. So we were now under the assumption that it must be the FPCM. So out I went and purchased a second from the wreckers. Plugged it in. No luck.

So this is where I'm at at the moment. Dropping resistor not the problem. FPCM not the problem. Pump only works on full voltage.

Does anyone here have any other ideas as to what the problem might be?

What are the consequences of running the pump full voltage?

[r33gtrv-spec]

Anyone?

Car details for those who really want to help a brother out.

R33 GTR V-Spec S1.

Stock fuel pump.

Stock injectors.

New Compustar alarm (was just fitted when this problem arose - Installer swears this is not the issue, can't really argue otherwise considering he took it all back out trying to diagnose the problem).

Just cam out of the sprayshop with a full respray (unrelated, but it's made me super paranoid of it being marked or damaged again)

New TE37SL wheels from Japan (also unrelated but the stress these wheels have caused me in trying to keep them flawless is sending me crazy)

Like I said, I really need help in trying to diagnose this issue. It seems to be running fine now I've bypassed the FPCM. Should I be concerned or is it fine to run my pump at high voltage?

Prize for any help. Booby prize for everybody else.

[Hadouken]

run a direct feed from the battery via relay. You need to do this in anycase if you are going to run a aftermarket fuel pump.

Look up the diy on here.

[r33gtrv-spec]

Yea i've earthed it direct. Completely bypassed the -ve. I will eventually upgrade my fuel pump, just not sure when. All out of coin now. But she looks tough and well worth every cent of my savings lol.

Is this gonna cause any problems running my stock pump? What are the side effects of having my pump run on full voltage at all times?

[Hadouken]

running rich.

you still havent wired your fuel pump up to support the extra current that will be dragged through the shitty old wiring on the positive side.

[KiwiRS4T]

New pump. Directly wired as per the 2 tutorials on this site.

[r33gtrv-spec]

Is it possible my pump could be on the way out as to why i'm having this issue? or maybe it's a wiring issue to the resistor which could be the problem?

[Hadouken]

Wiring is know to kark it. Google it. And your fuel pump is 20 odd years old. Why do you think?

[Duncan]

I just wanted to clarify, there is no issue with running the pump at full voltage at all times, it certainly won't cause it to run rich or anything like that (the fuel pressure regulator manages pressure, the pump has no impact unless it can't provide full pressure to the FPR - in which case your engine will almost certainly go bang).

I guess they run at lower voltage stock to keep the fuel cool by not pushing it through the system unnecessarily. It returns to full voltage once you leave idle anyway.

One thing to watch, the ECU uses the negative side to stop the pump running when the engine isn't (after priming) so you do still need the negative from the ECU. If you directly earth the pump you will lose that important safety feature.

[r33gtrv-spec]

Thanks guys, really appreciate all your help.

[discopotato03]

GTRs use a three step earth return system for the fuel pump . The fuel pump control module has switching to allow high resistance (two resistor banks in circuit) , low resistance (one resistor bank in circuit) or no resistance (no resistor banks in circuit) .

There are from memory two wires from the ECU to the FPCM to switch in/out bypasses for the two separate resistor banks .

If you've tried good FPCMs and you still don't get an earth return for the pump the issue may be upstream of it so no matter what it does you get an open circuit .

If you can get the relevant wiring diagrams you could try running your new pump earth to the appropriate FPCM wire and create a new earth on the down stream side of it . You know your new earth circuit works so if you splice a healthy FPCM into it the system should work like Nissan had it .

A .

[Dose Pipe Sutututu]

One thing to watch, the ECU uses the negative side to stop the pump running when the engine isn't (after priming) so you do still need the negative from the ECU. If you directly earth the pump you will lose that important safety feature.

but that negative goes to a relay which triggers a positive feed to the fuel pump. Connecting the pump's earth directly to the chassis won't affect its on and off ability

[timmy94]

On 8/2/2015 at 10:10 AM, Hadouken said:

run a direct feed from the battery via relay. You need to do this in anycase if you are going to run a aftermarket fuel pump.

Look up the diy on here.

What is the cause to the lower voltage in these fuelpumps?

[Duncan]

2 things; the wiring was only just big enough for the factory pump when it was shiny and new 30 years ago, often leading to voltage drop issues after all these years, and second is a computer on the earth with reduces the current at lower rpm to try and stop too much fuel being pumped.

It was probably overly complex 30 years ago, and today it is much better with a modern fuel pump to feed it full battery voltage and use you ECU to control it if you are worried about warming up the fuel by circulating it too much 

[joshuaho96]

On 7/29/2022 at 1:54 PM, Duncan said:

2 things; the wiring was only just big enough for the factory pump when it was shiny and new 30 years ago, often leading to voltage drop issues after all these years, and second is a computer on the earth with reduces the current at lower rpm to try and stop too much fuel being pumped.

It was probably overly complex 30 years ago, and today it is much better with a modern fuel pump to feed it full battery voltage and use you ECU to control it if you are worried about warming up the fuel by circulating it too much 

The other concern is that the dinky factory FPR cannot flow very much and if you're trying to push 300 lph of fuel through it while only injecting enough fuel to idle you will overshoot the FPR target fuel pressure.