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Recommendations on dropping fuel pressure RB26

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Hi i have been dealing with some fuel pressure issues and am looking for a recommendation. Vehicle is an R32 Gtr with RB26. Fuel setup is a Walbro 450 HP pump with a battery fed 8 awg circuit. 3/8" fuel lines, larger diameter fuel rail and Tomei type S regulator. Really the engine is not in a highly tuned state right now, I'm just beginning to bring the boost off of wastegate pressure (15pisg) with tuning and noticed the injectors are prematurely maxing out as well as the VE table numbers seeming to be higher than normal. (low 120's at high load) So I went ahead and fitted a honeywell pressure sensor and plumbed it in to log fuel pressure data, also at the same time cleaning/inspecting the entire fuel system. Currently the fuel pressure slowly drifts form the MAP as boost builds to 15psig which is about 4.5 psi lower than expected at that level. pressure seems consistent/repeatable but low and I expect would diverge more with more pressure. tests under no load confirm that the regulator responds like it should with 1:1 rise but not at load. I'm about to buy a new regulator to try but I thought I'd get a little feedback. Did I make a mistake on a Tomei type S? Or maybe I failed to check something. I was considering stepping up the pressure until I logged it and saw the diverging pressure. the attached picture is from a WOT run. Any thoughts are appreciated.

Attached Files

That gauge wire should certainly be up to the job - I assume it is a fused, relayed feed from the battery, but what about the return/ground side, it also has to be up to the job? There will be a graph for pressure/flow/voltage available - can you monitor the voltage drop across the pump under load to check it has the minimum to maintain the required pressure/flow required?

The Tomei S should be up to the job, but there are a lot of counterfeits around and if you were tricked into buying one of them, all bets are off -

When you checked and cleaned the fuel system, did you remember to check the tank 'sock', and a suitable pump pre-filter is used? Can't recall, but does that pump have an internal filter on the inlet and was it checked?

Right on the pump circuit, its fused with a relay. The ground is 8 awg also and just goes to the chassis. I also got rid of the factory pin connector on the hangar and soldered the wiring directly to the pump pigtail connector. I'm relatively sure I purchased a genuine regulator as I had heard about the fakes and used a reputable distributor. On the fuel system cleanout I did replace the tank sock and went as far as replacing the injector baskets even though all this stuff is basically new.

I'll have to perform the voltage test and see what I come up with. I had basically assumed it to be good with the wiring and low load voltage. I'll need to report back on that.

I once had a fuel pump relay that would vibrate and drop the power at high-RPMs. Put a digital voltmeter on the pump and watch it during a dyno pull.

Hi Johnny

David Is bang on here

another check is to test the flow returning to the tank you should be seeing at least 2 litres per min returning you may well find the fuel pump and or reg are the actual issue even tho they are new, it sounds like you have the wiring side covered but as stated above to check the voltage is following what the ecu is seeing or close to would be a great check also,

OK back with some test results.

Test 1 - voltage measured at pump during run

Pump voltage ~13.15 V: Pressure results were identical: Controller voltage logged ~13.6 V

Test 2 voltage measured at pump with the relay wires jumped with a wire.(no more relay in the picture)

Pump voltage ~13.15 V: Pressure results were identical: Controller voltage logged ~13.6 V

So basically no change and reviewing the IDC and some math I just picked a point about 5000 rpm to check fuel flow. Its about 42 gal/ hr and relating it to the flow curve for the pump under my conditions the pump should flow should be capable of 58 gal/hr or so.( pretty large gap) At this point I suppose it's the pump or the regulator. I dont have a good method to check the return flow under load which would identify my problem.

Any recommendations on tried and true pump / regulator brands from experience?

Is it possible that the pump basket in the tank(specific to the skyline and unlike anything else Ive ever seen) is somehow restricting flow to the pump?

Maybe before I buy more things I'll construct some sort of test to get the pump out of the basket.

Hello just from my experience on these cars a few things come to find here,

1: a loose hose clip inside the tank on the pressure side of the pump.

2: split hose same area oh internally perished hose restricting it

3: wiring from the pump to the fuel tank lid this is common

4: i prefer 044 pump adapted sock,

i recommend using a safe way to test the return flow to the tank which you i use the HV electronics combo flow meter, pressure sensor and E85 meter in my own dyno shop this has proven its worth in its first month of ownership

Regards Ross

OK so I though I'd close the loop on this for future reference. lots more inspection, no leaks or blocks. I also found and installed an in tank dual mounting adapter for the pump in the skyline. (shout out to OSTDyno, very reasonable) and relocating the pump made no difference. :( After testing my pump flow at pressure it is in spec at the intended pressures. It flows about 80 gal/hr at the point where I need 42 gal/hr. ( I misread the pump curve the first time) So after a call to the manufacturer about my tests I determined the regulator to be at fault. With some more searching I believe the issue is the "regulation slope" of the regulator. I found a nice writeup for this on . So I can either spend some money on a better regulator with about half the slope of the Tomei and still raise the pressure a little, or just raise the pressure sufficiently to bring the IDC into a reasonable range.

Which injectors do you have?

i have also seen the fuel pulsation dampner inside the fuel tank to leak. If you still have that try removing it.

i normally stick to turbosmart fpr1200 or gfb fx-r regs with bigger pumps.

the injectors are DW 800 cc/min units. and its a pump gas engine. currently there is no damper in the system. Thanks Ill take a look at those regulators

and for final closure on this I went with an FPR1200 after doing some spec reading and it fully solved the problem. its a nice regulator and worth the money. also for the record a tomei type s regulator is probably better suited for 255 lph and less flow applications. I could have used it but didnt want to fudge the fuel pressure.


Excellent :)