First attempt at Fuel Map - Road Tuning R32 GTR RB26

[Japtastic141]

Just a small update to this. Spent some time today testing the alternator and then the fuel pump again. Once again I can't find anything wrong lol...

Fuel Pump Scope - Amps up from cruising @ 6A to 8A @ on a power run. As you can see, the voltage doesn't budge.

https://ibb.co/y4s2SkH

Next is the alternator on a power run. Again, all looks fine. Voltage doesn't dip whatsoever..

https://ibb.co/bLBRSH3

Still clueless as to what is causing this. 

Will try to figure out why ECU is seeing a voltage dip. I've checked the obvious areas and continuity/voltage drop and run a new earth to the ECU so not sure where to look next but will try.

[dx4picco]

what fuel line do you have between pump and fuel rail?

is there any chance it's too small to support the flow without pressure drop?

[Japtastic141]

Just the standard 8mm ID. Only running stock power at the moment so plenty big enough + return flow test comes out good.

[Japtastic141]

Another update. Found this little *?@**! weeping. After taking it off it was clear it was split all the way through and leaking. It's the small pipe that comes off the hard line to connect to the filter deep in the engine bay.

Very hidden from view and couldn't see it leaking when doing any pressure testing with the Mytivac.

Either it wasn't at idle or engine off or I didn't spot it. Not sure why it wouldn't leak at idle (or maybe only a tiny amount) but my only theory is that under load the injectors turning on and off at a much higher rate than at idle caused the little splits in the pipe to open and up and release pressure and spit fuel over the little shelf. Which is also why I couldn't see any leaks under the car when checking even after a fast run and pulling over to check. You can see that the fuel leak has caused some corrosion.

Now, unfortunately, although finding that was good it still hasn't fixed my issue. I was so hopeful when I saw it and fixed it that this would finally be the issue fixed 

Looking at my old logs it looks like around a 10-20kpa differential fuel pressure improvement from fixing that leak..... But I've also moved the fuel pressure sensor directly attached to to the FPR rather than T'd off so it may just be the move of sensor has improved things. The signal certainly looks a lot smoother.

So now looking at around 30-40kpa difference vs 40-50kpa. What's considered normal / acceptablele?

Does anyone have an screenshot of a normal fuel differential log? How much does it normally drop or is it normally pretty flat?

[Japtastic141]

On 4/19/2024 at 1:09 AM, Adamw said:

All mechanical regulators have what is known as a pressure gradient or regulation slope.  Pressure varies with flow and the pressure control is never perfectly 1:1 with the boost reference. The slope is typically around 0.25kPa/LPH but some are much worse than others.  I think your last pic with the pressure dropping 60Kpa is more than just the regulation slope though, it looks more like a supply restriction or lack of pump.       

@Adamw Could I check what the 0.25kpa/lph would equate to in a kpa drop please. I see some FPR’s publish this but can’t find Tomie data anywhere yet. I found some other FPR’s publish 3psi/gpm. Also what made you think the 60kpa drop was a restriction rather than normal slope?

I’m seeing a few posts and comments about the Tomie and Sard FPR’s not holding 1:1 and slopes being worse than others but nothing from the manufacturer. I’m asking my supplier today if they have that data.

I may have butchered this completely but if I base this on 300bhp using 108 litres per hour at full throttle / power.

0.25kpa x 108 = 27kpa. 

If this is correct and the Tomei FRP isn’t the greatest, it does get me in the 40kpa slope ball park I’m in and if so would that be acceptable to tune around or does is still look too far off / wrong in your opinion?

[Japtastic141]

I'll update this later properly but swapping the Tomei Type S FPR to a Turbosmart FPR6 has fixed the problem of dropping such a big amount. It wasn't the only problem as I'll update later.

The spikes now down only happen when I let the throttle off as you can see then it's back to normal. 296kpa is reported as a baseline so now only dropping 10-12kpa at a maximum while on 1 bar of boost and 7k RPM! Well happy!

[Japtastic141]

Ok, will keep it fairly short but essentially I had multiple issues.

The original old fuel pump and FPR were well past their best.

The replacement 450lph Walbro was overpowered for my setup and wiring.

Wiring was replaced but the problems persisted.

Out-of-sight fuel hose was leaking but seemed to be only under high load and not at idle even with the Mytivac bringing fuel pressure up to 5Bar.

Once the fuel hose was replaced, the fuel pump swapped to a 255lph Walbro and FPR replaced, the problem was essentially fixed.

What skewed the results after everything was fixed was that the Tomei FPR has a very bad regulation slope. @Adamw Said the typical slope is around 0.25kpa / LPH.

Tomei Type S (and probably the Type L) = 0.43kpa / LPH which equates to a 47kpa loss at the high rev range. This matches what I found online and my own logs.

Turbosmart FPR6 (and their other models) = 0.16kpa / LPH which equates to a 10kpa loss at the high rev range. Which again matches very closely to my logs now.

I hope someday this whole thread is useful to someone in the same situation. Got to say a big thanks to everyone who helped as well. I've learnt a huge amount. Really appreciate it.

Now back to tuning the car which is a lot more fun than troubleshooting this!