Jump to content
SAU Community

Fuel Pressure Problem.

StealthX

By StealthX,
in Engines & Forced Induction

 Share

Recommended Posts

StealthX Veteran

StealthX

Posted
Posted

Hey guys. A little issue came about when my car went in to get tuned the other day.

It's a GT2860rs turbo, walbro 255lph pump, WRX 440cc injectors and an EMS standalone engine computer.

Now from stock, the X-Trail runs a returnless fuel set-up. i.e. no FPR, no return lines. The fuel pressure is governed at the tank, gosh darn knows how... All i know is it has about 52psi of fuel pressure in the rail, and at this 13psi of boost, its dropping.

Here's the dyno graph of power vs AFR:

(remember that power figure is at 4 wheels, not just 2!)

P1000847.jpg

P1000848.jpg

I'm starting to go lean at 13psi as you can see...

I'm not sure if my injectors are maxing out, but I wouldn't imagine they would cause this type of problem, would they?

WHATS GOING ON!??

p.s. the reason for my wacky boost curve is the dump, its getting sorted soon...

Link to comment
https://www.sau.com.au/forums/topic/318580-fuel-pressure-problem/
Share on other sites
Crans Mentor

Crans

Posted
Posted

the OEM fuel pressure regulation system probably isn't designed for boosted applications. Might be a good idea to rip it out set up the fuel pump to supply the fuel rail and put a FRP on the fuel return as per your normal Skyline setup

StealthX Veteran

StealthX

Posted
  • Author
Posted

Yeah that's what i thought. I just went for a drive with the laptop hooked up looking at injector shit.

Under full boost, they never got close to maxing out, i didnt see them go over 70% even at top revs.

@ zebra, i dont really know how big they are mate...

zebra Grand Master

zebra

Posted
Posted

With out a rising rate / boost referenced fuel reg the +ve manifold pressure forces back against the incoming fuel.

so although the injectors are seeing 52psi under vacuum, with 13psi in the intake they really only have 39psi of effective pressure.

which no doubt is causing the lean off.

Harey Veteran

Harey

Posted
Posted (edited)

Quote from here: http://www.aa1car.com/library/returnless_efi.htm

" A returnless fuel injection system, by comparison, manages fuel pressure a little differently. Instead of using a spring-loaded vacuum diaphragm in the regulator to change fuel delivery when throttle opening and intake vacuum change, the regulator in a returnless system operates at a constant pressure. The older return-type systems need to vary fuel pressure to maintain the same pressure differential across the injectors when intake vacuum drops. When vacuum drops, the regulator increases pressure to compensate. But in a returnless system, this isn't necessary because the line pressure is always the same.

So how does the system compensate for changes in engine load and vacuum? A returnless system uses the Powertrain Control Module (PCM) to regulate fuel delivery. A fuel pressure sensor mounted on the supply rail allows the PCM to monitor fuel pressure. When pressure in the supply rail drops as engine load or speed increase, the PCM compensates by increasing injector duration (on time) and/or the operating speed of the fuel pump."

1psi of boost basically reduces the fuel pressure by 1psi. Therefore, if the fuel pressure going in is 52psi, under 13psi of boost, the fuel rail pressure will only be 39psi! The only way to combat this is for the ecu to get more out of the injectors, however the injectors can only flow so much fuel at 39psi. I am assuming your tuner cant put in any more fuel, therefore if you dont want to change the fuel system design I believe you need bigger injectors.

Edited by Harey
Harey Veteran

Harey

Posted
Posted (edited)
Under full boost, they never got close to maxing out, i didnt see them go over 70% even at top revs.

That is very strange, I would be quizzing your tuner and saying why dont you put more fuel in??

As said above, your ecu needs to compensate for the lack of effective fuel pressure. I ran a turbocharged car with 43psi of effective fuel pressure, so I dont see why you cant on 39psi. You just need your ecu and injectors to compensate.

Edited by Harey
StealthX Veteran

StealthX

Posted
  • Author
Posted
That is very strange, I would be quizzing your tuner and saying why dont you put more fuel in??

As said above, your ecu needs to compensate for the lack of effective fuel pressure. I ran a turbocharged car with 43psi of effective fuel pressure, so I dont see why you cant on 39psi. You just need your ecu and injectors to compensate.

Yeah Andrew did, you can see the A:FR drop rich just before it starts to go lean, so he tried. I dunno about just then if i read the duty cycle correctly, it was hard to read the computer screen, wrestle with the steering wheel from the torque steer/wheel spin AND watch the road at the same time...

Thanks for the help! looks like i might just fix this boost curve and run a flat 10psi, then avoid touching the fuel system at all, cos its a prick of a job on my car entire intake manifold needs to come off just to get to the injectors!

R31Nismoid Grand Master

R31Nismoid

Posted
Posted
the OEM fuel pressure regulation system probably isn't designed for boosted applications. Might be a good idea to rip it out set up the fuel pump to supply the fuel rail and put a FRP on the fuel return as per your normal Skyline setup

Exactly what I'd do :)

Rip the shit out from the tank end, run the pump... fit a FPR up the front and run a return line back and problem solved.

Harey Veteran

Harey

Posted
Posted (edited)
Exactly what I'd do :)

Rip the shit out from the tank end, run the pump... fit a FPR up the front and run a return line back and problem solved.

Yes that would be the best solution, but its far from simple.

39psi can be enough fuel pressure if the injectors can flow enough fuel (also if the fuel pump can flow enough).

Increasing the voltage to the stock fuel pump could also be enough. It doesnt look like it needs a lot more fuel. Whether you do this by running dedicated power cables from the battery or you use a voltage amplifier.

Edited by Harey
StealthX Veteran

StealthX

Posted
  • Author
Posted

Thatt was a great article Jeff, thanks!

For now I might focus on fixing that boost curve... 13psi is too much for what I wanted, so I think I'll address that issue rather than the fuel system... The guys in the US who mod these QR25 engines use return setups with fprs so I'll go with that sorta setup of I need more fuel. At the moment Im pretty close to the limit of the stock block and the chassis, I desperately need some suspension mods and a bit more rubber (I've only got 215s at the moment) for some better handling/traction.

I'm armed with all these options now, so that's great!

Thanks guys!

femno Grand Master

femno

Posted
Posted

Not having enough fuel pressure in the rail seems dodgy.

If I wanted to feel comfortable driving the car hard and wanted to know the setup was solid, id do things properly.

440 injectors for 220HP is heaps. I think changing injectors out is masking the real problem of a weak fuel system.

It aint good to run shit on the limit, especially fuel.

Braise a fitting on the end of the rail, run a Sard reg, and run an extra line to the rear for the return. Also hard wire the pump. Ditch the Walbro and go 040. Piss easy.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted
The walbro dropped in perfectly, needed no wiring/plumbing mods at all...

So basically you probably haven't wired it correctly...

You need to ensure the pump has the correct voltage it requires!

Bolt-in does not mean "work correctly (especially on a N/A previously setup)...

StealthX Veteran

StealthX

Posted
  • Author
Posted
So basically you probably haven't wired it correctly...

You need to ensure the pump has the correct voltage it requires!

Bolt-in does not mean "work correctly (especially on a N/A previously setup)...

I see where you're coming from, cos in theory, the bigger pump should need different voltages!

According to the guys in the US with the same motor, the walbro is a direct swap. uses the same voltage as the stock one as far as i know.

Hundreds of guys have done turbo setups, similar to mine and there's not one mention of altering the wiring at all, that's why i chose the 'bro over a bosch. They are a drop in and (usually) good for upwards of 400whp.

Just talked to Andrew on the phone and he said the pump and/or injectors are fine for well over the power im making, so im leaning (pardon the pun) towards the stock in-tank regulator doing weird things and not having enough pressure to support the boost.

Either way its not a huuge problem, its only starting to lean out on 13psi and 5500 revs, and on the street in the last 2 days, i havnt seen 13psi yet. The load on the dyno is substantially more than on the street in 1st 2nd and 3rd gears so hopefully i wont have much of an issue to deal with.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Testing the voltage is such a simple thing to check mate, to simply rule out that it's not an issue I'm not sure why it wasn't done?

Just because other people drop in and it works is great, but doesn't automatically mean that voltage isn't your problem if you've not checked it.

StealthX Veteran

StealthX

Posted
  • Author
Posted

Ok sure I'll have a look. what should the voltage be? Won't it be hard to measure?

I was under the impression that said voltage changes with fuel needs in a returnlessn system, so it would be hard to be in the back seat with a voltmeter, when I need to vary the engine conditions to check!

Or am I mistaken?

rob82 Mentor

rob82

Posted
Posted (edited)

In the 30 odd so of boosted Gen3 and 4 I've tuned I've never had an issue up to 350rwkw and 10Psi of boost using the std 1 one way fuel system - they do however have injector flow scaliing vs injector pressure drop. There is no reason to swap to a return system you have an aftermarket ECU - just tune around its not like the ems has any brains anyway. There should be no reason to assume fueling wont be consistant.

The things I would be checking is whether or there is a fuel pump controller. It maybe PWM if the std ecu is still controlling the fuel pump side of things.

Edited by rob82

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • hoodedreeper
      Chris' Toyota Mark ii JZX110

      By hoodedreeper · Posted

      Next on the to-do list was an oil and filter change. Nothing exciting to add here except the oil filter is in a really stupid place (facing the engine mount/subframe/steering rack). GReddy do a relocation kit which puts it towards the gearbox, I would have preferred towards the front but there's obviously a lot more stuff there. Something I'll have to look at for the next service perhaps. First time using Valvoline oil, although I can't see it being any different to most other brands Nice... The oil filter location... At least the subframe wont rust any time soon I picked up a genuine fuel filter, this is part of the fuel pump assembly inside the fuel tank. Access can be found underneath the rear seat, you'll see this triangular cover Remove the 3x plastic 10mm nuts and lift the cover up, pushing the rubber grommet through The yellow fuel line clips push out in opposite directions, remove these completely. The two moulded fuel lines can now pull upwards to disconnect, along with the wire electrical plug. There's 8x 8mm bolts that secure the black retaining ring. The fuel pump assembly is now ready to lift out. Be mindful of the fuel hose on the side, the hose clamp on mine was catching the hose preventing it from lifting up The fuel pump/filter has an upper and lower section held on by 4 pressure clips. These did take a little bit of force, it sounded like the plastic tabs were going to break but they didn't (don't worry!) The lower section helps mount the fuel pump, there's a circular rubber gasket/grommet/seal thing on the bottom where the sock is. Undo the hose clip on the short fuel hose on the side to disconnect it from the 3 way distribution pipe to be able to lift the upper half away. Don't forget to unplug the fuel pump too! There's a few rubber O rings that will need transferring to the new filter housing, I show these in the video at the bottom of this write up. Reassembly is the reverse Here's a photo of the new filter installed, you'll be able to see where the tabs are more clearing against the yellow OEM plastic Once the assembly is re-installed, I turned the engine over a few times to help build up fuel pressure. I did panic when the car stopped turning over but I could hear the fuel pump making a noise. It eventually started and has been fine since. Found my 'lucky' coin underneath the rear seat too The Youtube video can be seen here: https://www.youtube.com/watch?v=uLJ65pmQt44&t=6s
    • hoodedreeper
      Chris' Toyota Mark ii JZX110

      By hoodedreeper · Posted

      It was picked up on the MOT/Inspection that the offside front wheel bearing had excessive play along with the ball joint. It made sense to do both sides so I sourced a pair of spare IS200 hubs to do the swap. Unfortunately I don't have any photos of the strip down but here's a quick run down. On the back of the hub is a large circular dust cover, using a flat head screw driver and a mallet I prised it off. Underneath will reveal a 32mm hub nut (impact gun recommended). With the hub nut removed the ABS ring can be removed (I ended up using a magnetic pick up tool to help). Next up is to remove the stub axle, this was a little trickier due to limited tools. I tried a 3 leg puller but the gap between the hub and stub axle wasn't enough for the legs to get in and under. Next option was a lump hammer and someone pulling the stub axle at the same time. After a few heavy hits it released. The lower bearing race had seized itself onto the stub axle, which was fine because I was replacing them anyway. With the upper bearing race removed and the grease cleaned off they looked like this The left one looked pristine inside but gave us the most trouble. The right one had some surface rust but came apart in a single hit, figure that out?! I got a local garage to press the new wheel bearings in, reassemble was the opposite and didn't take long at all. Removing the hub itself was simple. Starting with removing the brake caliper, 2x 14mm bolts for the caliper slider and 2x 19mm? for the carrier > hub bolts. I used a cable tie to secure the caliper to the upper arm so it was out of the way, there's a 10mm bolt securing the ABS sensor on. With the brake disc removed from the hub next are the three castle nuts for the upper and lower ball joints and track rod end. Two of these had their own R clip and one split pin. A few hits with the hammer and they're released (I left the castle nuts on by a couple of turns), the track rod ends gave me the most grief and I may have nipped the boots (oops). Fitting is the reversal and is very quick and easy to do. The lower ball joints are held onto the hub by 2x 17mm bolts. The castle nut did increase in socket size to 22mm from memory (this may vary from supplier) The two front tyres weren't in great condition, so I had those replaced with some budget tyres for the time being. I'll be replacing the wheels and tyres in the future, this was to get me on the road without the worry of the police hassling me.
    • Haggerty
      RB25DE NEO with Haltech ECU

      By Haggerty · Posted

      Yep, the closest base tune available was for the GTT, I went with that and made all the logical changes I could find to convert it to Naturally Aspirated. It will rev fine in Neutral to redline but it will be cutting nearly 50% fuel the whole way.  If I let it tune the fuel map to start with that much less fuel it wont run right and has a hard time applying corrections.  These 50% cuts are with a fuel map already about half of what the GTT tune had.  I was having a whole lot of bogging when applying any throttle but seem to have fixed that for no load situations with very aggressive transient throttle settings. I made the corrections to my injectors with data I found for them online, FBCJC100 flowing 306cc.  I'll have to look to see if I can find the Cam section. I have the Bosch 4.9 from Haltech. My manifold pressure when watching it live is always in -5.9 psi/inHg
    • brillo
      Leak from Tokico BM50 Brake Master Cylinder

      By brillo · Posted

      Hi My Tokico BM50 Brake master cylinder has a leak from the hole between the two outlets (M10x1) for brake pipes, I have attached a photo. Can anyone tell me what that hole is and what has failed to allow brake fluid to escape from it, I have looked on line and asked questions on UK forums but can not find the answer, if anyone can enlighten me I would be most grateful.
    • MBS206
      Cas issue

      By MBS206 · Posted

      It will be a software setting. I don't believe many on here ever used AEM. And they're now a discontinued product,that's really hard to find any easy answers on. If it were Link or Haltech, someone would be able to just send you a ECU file though.
×
×
  • Create New...