Fuel Pressure drop at WOT!

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Koki Factory Racing
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Car: 1994 Nissan 180SX

Fuel Pressure drop at WOT!

Postby Koki Factory Racing » Thu Dec 03, 2020 9:35 am

Hello all, I'm new here.

Figured this problem i've been having should be shared to the forums. So recently I upgraded my turbo from the APEXI AX53B70 to the newly designed MMP NS400 Turbo. (.86 exhaust and .63 AR T2 stock replacement turbo pretty much.) After changing the turbo, I obviously went to get it tuned. Found out that the fuel pressures were dropping, causing the AFR to go SUPER lean. Fuel pressure would rise up until 6100 RPM and fall drastically to base pressures (38 psi). We changed to DW200 (255lph) and changed fuel filter to Z32 filter. Problem was still there. Left the tuner, installed an Aeromotive FPR, upgrading from the what looked like Nismo FPR. Problem still existed. We decided to run a separate, completely new fuel line above the car, it's own specific fuel filter to the feed. Although it held a little longer, fuel pressure still dropped almost similar. The new fuel pump was hard wired from the start, then hard wire with relay was done directly to the battery since it's in the back. I've ran out of ideas. If this situation has been on here, I apologize and ask that you direct me to that forum with a link.

Upgrades that have been done since but not taken back for tuning are:
AEM 340lph In tank fuel pump
FiveO 750cc side feed injectors.
PS: Turbo was at 18psi, with the 6000 rpm pull, the car made 366 WHP but for safety precautions further tuning was not done. Please guys help me out! Thank you in advance!


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AZhitman
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Re: Fuel Pressure drop at WOT!

Postby AZhitman » Thu Dec 03, 2020 9:08 pm

Welcome aboard!

Dumb question: Is the FPR before or after the fuel rail?

Koki Factory Racing
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Joined: Tue Dec 01, 2020 5:43 pm
Car: 1994 Nissan 180SX

Re: Fuel Pressure drop at WOT!

Postby Koki Factory Racing » Fri Dec 04, 2020 8:44 am

AZhitman wrote:
Thu Dec 03, 2020 9:08 pm
Welcome aboard!

Dumb question: Is the FPR before or after the fuel rail?
After. The return line gets fed in to the FPR then goes return like normal. Fuel pressures were dropping before changing to the new FPR with the Nismo one which is on the rail itself.

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AZhitman
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Re: Fuel Pressure drop at WOT!

Postby AZhitman » Fri Dec 04, 2020 9:00 am

Only thing I can think of is a line is collapsing, or the pickup is cavitating at the tank.

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PapaSmurf2k3
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Re: Fuel Pressure drop at WOT!

Postby PapaSmurf2k3 » Sun Dec 06, 2020 10:53 am

What's your injector duty cycle?
You might be able to just drop your base fuel pressure and increase duty cycle so you don't have the pressure drop issue. Pumps flow more at lower pressure.
You could also try running a 2nd pump, or larger fuel line.

Also take a look at your line voltage at those higher RPMs. Maybe your alternator is going out or something and isn't putting out the voltage you should have.

Koki Factory Racing
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Car: 1994 Nissan 180SX

Re: Fuel Pressure drop at WOT!

Postby Koki Factory Racing » Sun Dec 06, 2020 7:35 pm

PapaSmurf2k3 wrote:
Sun Dec 06, 2020 10:53 am
What's your injector duty cycle?
You might be able to just drop your base fuel pressure and increase duty cycle so you don't have the pressure drop issue. Pumps flow more at lower pressure.
You could also try running a 2nd pump, or larger fuel line.

Also take a look at your line voltage at those higher RPMs. Maybe your alternator is going out or something and isn't putting out the voltage you should have.
Tuner said he had the injectors past 100% to try and trick them into getting more fuel. I kinda scratched my head at that 'cause I thought I had 550cc's. If that's the case, I think my previous injectors were smaller than that, hence why they were at 100% + duty cycle. What larger fuel line would you recommend?

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Re: Fuel Pressure drop at WOT!

Postby PapaSmurf2k3 » Sun Dec 06, 2020 10:31 pm

I'd do the larger fuel line last. The factory size should be able to flow plenty of fuel... I'm just wondering if the diameter is causing restriction.
Was the fuel filter you removed ok?

Koki Factory Racing
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Re: Fuel Pressure drop at WOT!

Postby Koki Factory Racing » Mon Dec 07, 2020 7:53 am

PapaSmurf2k3 wrote:
Sun Dec 06, 2020 10:31 pm
I'd do the larger fuel line last. The factory size should be able to flow plenty of fuel... I'm just wondering if the diameter is causing restriction.
Was the fuel filter you removed ok?
Before replacing it with the Z32 fuel filter, it was really dirty. It shocked me because it was literally the OEM Sr20det fuel filter, so swapping with the z32 was a significant change.

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PapaSmurf2k3
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Re: Fuel Pressure drop at WOT!

Postby PapaSmurf2k3 » Mon Dec 07, 2020 5:19 pm

Hmmm... I wonder if you've got some trash in the tank clogging up the pump sock and even your new filter. Maybe check them again...


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