frustrating fuel pressure issue

[damnonrs]

hey guys, very long term lurker here. I always use the search function for most things but im stumped here. 

 

I got a built hks rb28 car from japan, it came with documentation of the build and dyno numbers, car should make around 600awhp. Ever since i received the car i hadnt floored it since it was tuned on japan fuel so i ordered a haltech 2500 and went for a tune locally. On the dyno we found that it was dropping fuel pressure from 4.1(idling pressure is at around 4 bar, i know that idle fuel pressure should be 3 bar this is another tell tale that somethings wrong ) to all the way leaning out so the tuner called it quits and told me i should probably replace my fuel pump. I ordered a bosch 044 with a new sock filter, 1050cc injectors, higher flowing fuel filter and a 30 amp relay for the fuel pump we also changed the fuel regulator to an AEM one.. went on the dyno and same exact problem occured except the tuner said its a little bit better. this time, he sent me off with a 6000rpm red line so i dont get into leaning out territory and keeping the car drivable. Here is what the car is doing on the fuel pressure with higher rpms. https://imgur.com/a/qjr8yuY the mechanic and tuner don't really know what the problem is and they are recommending to change all the fuel lines to new braided lines so everything is fresh or performing a fuel pressure test, i've spent close to 4k chasing this problem and im kinda burnt out. 

Could this be a leaking vent hose, either on the fuel tank or the charcoal cannister? maybe a bad fuel damper? replacing the fuel pump to a stronger one than before made car lean out a bit later in the rpms but still is running way too rich to lean, what could this mean? Any leads would help! 

thanks

Edited December 6, 2022 by damnonrs

[robbo_rb180]

A single Bosch 040 isn't big enough........
Go to a modern drop in TI or bosch probaly 2x 460lph with a new or modded hanger and stage the 2nd pump at like 3500rpm and 50% TPS

[damnonrs]

2 minutes ago, robbo_rb180 said:

A single Bosch 040 isn't big enough........
Go to a modern drop in TI or bosch probaly 2x 460lph with a new or modded hanger and stage the 2nd pump at like 3500rpm and 50% TPS

im using a bosch 044 which is good enough for 600ps. but bosch 040 you said is also good for 700hp. my car leans out at 450hp on the dyno, i dont think this is a fuel supply issue, i think im chasing a vaccum or fuel pressure problem.

[Murray_Calavera]

Did you recently purchase that Bosch 044? That fuel pump was released about 30 years ago and has been discontinued by Bosch... Even if it isn't a fake, there is no reason to use this pump over a modern fuel pump. 

If a pump is advertised as "supporting 600HP" that does not guarantee that it will indeed support 600HP on your build. Also, certainly the HP rating of the pump is at the motor and not at the wheels. 

There is a huge difference in the fuel pump requirement between a big NA V8 on pump 98 making 600HP and a small 4 cylinder turbo on e85 running 40+psi boost making 600HP.

In the defence of your 044, maybe it's 28 years old and has finally worn out lol. In any case replace the pump with something modern. I'd recommend starting with a Walbro 525 and going from there. You can always throw in a twin hanger and get a second one if need be later down the track. 

For $200 you can replace your dinosaur fuel pump and most likely resolve your issue. I don't understand why you are reluctant to do so. 

[robbo_rb180]

1 hour ago, damnonrs said:

im using a bosch 044 which is good enough for 600ps. but bosch 040 you said is also good for 700hp. my car leans out at 450hp on the dyno, i dont think this is a fuel supply issue, i think im chasing a vaccum or fuel pressure problem.

same thing ones internal one is external.
its 600hp is generous and at 4 bar of pressure and drops off shows its not big enough but hey what would I know..............


 

[damnonrs]

12 minutes ago, Murray_Calavera said:

Did you recently purchase that Bosch 044? That fuel pump was released about 30 years ago and has been discontinued by Bosch... Even if it isn't a fake, there is no reason to use this pump over a modern fuel pump. 

If a pump is advertised as "supporting 600HP" that does not guarantee that it will indeed support 600HP on your build. Also, certainly the HP rating of the pump is at the motor and not at the wheels. 

There is a huge difference in the fuel pump requirement between a big NA V8 on pump 98 making 600HP and a small 4 cylinder turbo on e85 running 40+psi boost making 600HP.

In the defence of your 044, maybe it's 28 years old and has finally worn out lol. In any case replace the pump with something modern. I'd recommend starting with a Walbro 525 and going from there. You can always throw in a twin hanger and get a second one if need be later down the track. 

For $200 you can replace your dinosaur fuel pump and most likely resolve your issue. I don't understand why you are reluctant to do so. 

My tuner put me on this fuel pump which actually made the flow a bit better than my previous pump. I attached a picture of what the car was doing in japan with a less flow fuel pump, we put it on a dyno here and it couldn’t even break 400hp with the fuel pump the car came with. Fuel pressure is all wacky and fluctuates. Also they made a new 044 pump  

[damnonrs]

I also want to mention that the car gets about 150km on a full tank with normal driving and just spews fire non stop

[Murray_Calavera]

7 minutes ago, damnonrs said:

I also want to mention that the car gets about 150km on a full tank with normal driving and just spews fire non stop

Post your ESP map. 

Log every channel and go for a drive. Post your data log. 

[Murray_Calavera]

 

22 minutes ago, damnonrs said:

My tuner put me on this fuel pump which actually made the flow a bit better than my previous pump. I attached a picture of what the car was doing in japan with a less flow fuel pump, we put it on a dyno here and it couldn’t even break 400hp with the fuel pump the car came with. Fuel pressure is all wacky and fluctuates. Also they made a new 044 pump  

Just a FYI. The 044 is indeed gone mate. 

https://www.bosch-motorsport-shop.com.au/blog/tech-product-overviews/the-044-is-dead-long-live-the-bosch-motorsport-200/#:~:text=After 28 years of setting,number%3A 0 580 254 044.

[GTSBoy]

Another vote for the "044 is too small". It is too small. We all learned 20 years ago that you would need more than one such pump to support the sort of power you're wanting.

As to your fuel consumption issue......that's most likely to be a tune thing. Do as advised above.

[Dose Pipe Sutututu]

Sounds like you need a new tuner, the fuel pump recommendation is one indicator that he/she may not be up to date with mainstream modern/proven products.

[damnonrs]

47 minutes ago, Dose Pipe Sutututu said:

Sounds like you need a new tuner, the fuel pump recommendation is one indicator that he/she may not be up to date with mainstream modern/proven products.

yea i kinda agree, hes smart and the car came with this problem from japan so it was the logical thing to go to a new fuel pump. but i agree maybe 044 wasnt the best choice. anyways the fuel pump is not the problem here, its a fuel pressure issue where it idles too high fuel pressure and drops under load.

 

I have attached some data logging. this was from the last time i drove the car, car is put to storage while im trying to figure out this problem. i think fuel pressure logging wasnt turned on by the tuner but i have attached a video of what the fuel pressure does under boost. https://imgur.com/a/qjr8yuY

I inspected every single line in the front and underneith. what im thinking is maybe a vaccum line or a vent line ontop of the fuel tank is broken and it cant build pressure under boost in the fuel tank. 

2022-12-06_0528pm_Logs323to386.csv

[Dose Pipe Sutututu]

Not sure if the GT-Rs use them, but is there anything between the fuel pump and fuel tank lid/cover? On the S15s (no idea why) there's an over pressure valve that dumps fuel back into the tank when fuel pressure goes above 4 ish bar.

Looks like this:

[damnonrs]

51 minutes ago, Dose Pipe Sutututu said:

Not sure if the GT-Rs use them, but is there anything between the fuel pump and fuel tank lid/cover? On the S15s (no idea why) there's an over pressure valve that dumps fuel back into the tank when fuel pressure goes above 4 ish bar.

Looks like this:

from the googling i did, i dont see anything like that. i also just tried priming the pump. it primes to 4.11bar and then drops to 1.1, are the pumps supposed to hold the pressure at around where it primes to? I also tried without the gas cap and it acts the same way as with it screwed on.

[robbo_rb180]

Does the car have an adjustable fuel regulator? If it does lower the pressure.

The way a fuel regulator works on these is there's a set base pressure (usually 3bar or just under with vac reference removed) and as manifold pressure increases so does fuel pressure. 

It still a fuel pump issue. As has been stated. Your American yeah? I'd listen to the Australian guys who have more than 30years of experience with this platform.

when the factory regs failed I've had low pressure not high.

@Dose Pipe SutututuI still think we should go over there and show them how to set these things up properly and tune more than just full throttle cells.

[Dose Pipe Sutututu]

There's a business idea!

Just timing couldn't be any worse, I'm a dad now - can't just bugger off for a tuning trip  

[damnonrs]

28 minutes ago, robbo_rb180 said:

Does the car have an adjustable fuel regulator? If it does lower the pressure.

The way a fuel regulator works on these is there's a set base pressure (usually 3bar or just under with vac reference removed) and as manifold pressure increases so does fuel pressure. 

It still a fuel pump issue. As has been stated. Your American yeah? I'd listen to the Australian guys who have more than 30years of experience with this platform.

when the factory regs failed I've had low pressure not high.

@Dose Pipe SutututuI still think we should go over there and show them how to set these things up properly and tune more than just full throttle cells.

I'm in canada lol

 

can you explain how the car as is in japan 4 years ago with a lesser flowing fuel pump than whats in there now was making 550rwhp and i can't get past 400 with the same exact setup except 4 years later. the car had been sitting for a bit. i dont know how else to explain its not a fuel pump issue unless the pickup is leaking. 

 

I understand how a fuel regulator works and buying a new regulator and playing with it could damage my engine. its the stock regulator on there which is good for heaps of power, the car has been tuned around this problem (which is no good i understand) i am trying to solve it and put it back on a dyno asap.

Edited December 7, 2022 by damnonrs

[Murray_Calavera]

1 hour ago, damnonrs said:

I'm in canada lol

 

can you explain how the car as is in japan 4 years ago with a lesser flowing fuel pump than whats in there now was making 550rwhp and i can't get past 400 with the same exact setup except 4 years later. the car had been sitting for a bit. i dont know how else to explain its not a fuel pump issue unless the pickup is leaking. 

 

I understand how a fuel regulator works and buying a new regulator and playing with it could damage my engine. its the stock regulator on there which is good for heaps of power, the car has been tuned around this problem (which is no good i understand) i am trying to solve it and put it back on a dyno asap.

It's very easy to explain, you can make a dyno show whatever power figure you want very easily. For all we know the car never really made a genuine 550rwhp, it's just what the dyno printout showed. 

I don't know why you are so focused on the past and what the car supposedly did in Japan. 

Why not just focus on the issues you have now and resolving those. 

[GTSBoy]

25 minutes ago, Murray_Calavera said:

you can make a dyno show whatever power figure you want very easily

Just hang the ambient air temp sensor over the top of the exhaust manifold, f'rigsample.

[damnonrs]

1 hour ago, Murray_Calavera said:

It's very easy to explain, you can make a dyno show whatever power figure you want very easily. For all we know the car never really made a genuine 550rwhp, it's just what the dyno printout showed. 

I don't know why you are so focused on the past and what the car supposedly did in Japan. 

Why not just focus on the issues you have now and resolving those. 

So you are telling me a reputable shop built and documented a 2.8 build by hand and gave the car to the customer that goes through a fuel tank in 100km and ran his car on the dyno leaning out and he drove it for 4-5 years like this? 
 

anyways I’m focused on the present. What would your next step be knowing all this?