2jzgte vvti Fuel pressure drop (Fuel Cut?)

[Brohan]

Hello everyone

I've been having some fuel problems with my engine, what happens is I take off lets say 2nd gear WOT and I was noticing that fuel pressure will start dropping once It starts going up in boost, I thought it was a fuel pump problem at first, but after confirming that the fuel pump is working with no issues I continue to look for other problems.
I did several pulls on 2nd gear and notice that my boost is going as high as 15-16psi, once it gets up there i also see that the fuel pressure starts dropping down from 60-75psi to 30psi then i let off.
Installed a HKS FCD and that does not help. so m running out of ideas on what it can be.

This is an Aristo 2jzgte vvti on stock ECU R154
3" exhaust from downpipe back no cats or muffler, possible problem here with the 3" downpipe right after the turbo.
Mid mount intercooler , 3" intake side piping, and 2.5" turbo side piping.
after market fuel pressure regulator
-6 fuel lines, Feed and return
deatschwerks fuel pump
12v fuel pump mod


car idles perfect
drives great only when i hit around 15-16psi is when I'm in trouble.

Cheers
Johan

[woggin]

Fuel pump supplies fuel, fuel regulator regulates the pressure.

There's 3 things to check here, the voltage at the pump, the pump and the regulator.

Wat did u do to confirm the pump is fine? Maybe as the motor demands more fuel, the pump can't keep the flow and pressure up.

Maybe the pump is internally failing under load. There's a couple things it could b, changing the fuel pump is one way of eliminating it as a cause, the other is changing the fuel pressure reg, both are a pain in the ass tho.

[woggin]

Additionally, if ur running out of fuel, the pressure starts dropping off (pump can't flow way the injectors are capable of)
You haven't mentioned if stock turbos either....

[Brohan]

yeah i haven't check for voltage at the pump, will try that today, i can change the pump out and try that out

the motor is still running on stock twins

[Brohan]

Just did a voltage, test at the pump and I'm getting 13.47 volts at the pump under load, going to swap out the pump with a walbro and see what happens

[Daddio]

Assuming you are measuring pressure in the rail and not before the pressure regulator....Why are you getting 60-75psi in the first place? Stock fuel pressure is around 35psi, which suggests that with your aftermarket regulator you are getting too much pressure at lower rpm (which is likely making the motor run a little rich) then dropping off to close to stock pressures at full boost. Appears to me your fuel reg is not doing its job properly?

[Brohan]

No yeah the fuel pressure at idle is 35psi

[lexsmaz]

So its a rising rate regulator ?? if so you are getting way to much fuel pressure increase ..

Also have you checked / changed the fuel filter too

[Brohan]

The fuel pressure rises when it starts going into bost (60-70psi fuel pressure) then it goes down, the filter is a brand new auromotive filter

[Draven]

To confirm - your fuel pressure is initially ok. When does it go up to 70psi (at what boost/rpm)? if it's hitting good boost then losing pressure higher up in the rev range, it would suggest a fuel volume issue (ie: pump or restriction) That's a lot of fuel pressure for ~15psi of boost. Was there a reason you went to an aftermarket reg? Stock fuel pump should be fine for that power (unless it's shagged).

The 3" downpipe will be causing your boost spike, but shouldn't be a fueling issue for stock pump

also (slightly off-topic), what is a mid-mount intercooler?

[wilbo666]

What fuel pressure regulator do you have? As said it sounds like you might have a non linear rising rate fuel pressure regulator, which is NOT what you want!

Page 8 of the following has a nice image of how the fuel pressure regulator acts so that the injectors "see" the same pressure all the time...

i.e. When the pressure in the intake drops, the fuel pressure also drops so that the pressure difference between the fuel rail and the intake manifold stays the same! (36 or 41psi depending on engine)... the reverse happens when "on boost", the fuel pressure is raised as a result of the pressure in the intake manifold.

http://www.autoshop101.com/forms/h22.pdf




That said the issue you have maybe a fuel pump issue... the amount of fuel that a fuel pump can flow decreases as pressure increases. I suspect that your fuel pump is unable to supply the required amount of "full load" fuel due to the very high fuel pressure your regulator is trying to achieve...!


Cheers
Wilbo

[Brohan]

Thanks for the help guys, wanted to let you guys know that I found the
Problem to my fuel pressure drop. Checked my tank and fuel pump assembly and
Saw that the pump was sucking a lot of crab and look in the tank and it was filty, so I just build a new fuel cell with an internal surge tank.
Long story short finished everything and went for a drive and no more fuel pressure drop and car runs amazing.

Here are some pics of the new setup.

[woggin]

hmmmmm sxc! good to hear u found the issue!

very elaborate fix tho isnt it?

[Draven]

holy crap that's a pretty fuel tank

[Brohan]

hmmmmm sxc! good to hear u found the issue!

very elaborate fix tho isnt it?

thanks man, yeah i always said that if i run into fuel tank issues is switch over to a fuelcell and make it so that i wont have to ever change anything other than filters agian and not worried about it.

holy crap that's a pretty fuel tank

thanks dude!