So,

I had my 03 z on the dyno tonight (mustang dyno). I have an AAM stg 1 RFS with rc 750cc injectors, and Walbro 255 pump. I also have a Vortech supercharger on the car with 2.87 pulley. Running Uprev Osiris for management.

The runs were going great and we were making decent power, but then couldn't get enough fuel above 5800 ish rpm. No matter the changes we made it kept wanting to lean out. So after a couple failed attempts to rich it up some we watched the fuel pressure gauge during a pull.

Base pressure was aprox 50 psi, during the pull pressure would fall from 50 all the way down to maybe 10psi. Now with the A1000 regulator it should be increasing 1:1 per pound of boost. Took the vacuum line off still did the same thing. Tried increasing the base pressure, same thing.

Now I'm just wondering your opinions on if it's the regulator that's screwed or the pump...??

Car ended up making 380whp and 318wtq only reving to 5800. Afr's up to that point were still pretty rich too. I want to get this problem figured out so we can finish off and make over 400whp

Thanks for any input

 

pic of the car for anyone curious.

 

the stage 1 AAM RFS removes the pressure regulator in the fuel basket right? I know the CJM ones does.

If it does, then your have a bad fuel pump. It might be the non-high pressure model or its relief valve might be fubar. If it was new, exchange for new one.

 

1. Remove fuel pump fuse located in IPDM E/R.
2. Start engine.
3. After engine stalls, crank it two or three times to release all fuel
pressure.
4. Turn ignition switch “OFF”.
5. Reinstall fuel pump fuse after servicing fuel system.
ITEM SPECIFICATION
Idle speed A/T: 650±50 rpm (in “P” or “N” position)
M/T: 650±50 rpm (in “N” position)
Ignition timing A/T: 15±5° BTDC (in “P” or “N” position)
M/T: 15±5° BTDC (in “N” position)
SEF214Y
PBIB1094E
EC-54
BASIC SERVICE PROCEDURE
Revision; 2004 April 2003 350Z
FUEL PRESSURE CHECK
NOTE:
Use Fuel Pressure Gauge Kit (J-44321) to check fuel pressure.
1. Release fuel pressure to zero. Refer to EC-53, "FUEL PRESSURE RELEASE" .
2. Install the inline fuel quick disconnected fitting between fuel
damper and injector tube.
3. Connect the fuel pressure test gauge (quick connector adapter
hose) to the inline fuel quick disconnected fitting.
4. Turn ignition switch ON and check for fuel leakage.
5. Start engine and check for fuel leakage.
6. Read the indication of fuel pressure gauge.

At idling: Approximately 350 kPa (3.57 kg/cm2 , 51 psi)

7. If result is unsatisfactory, go to next step.
8. Check the following.

Fuel hoses and fuel tubes for clogging

Fuel filter for clogging

Fuel pump

Fuel pressure regulator for clogging
If OK, replace fuel pressure regulator.
If NG, repair or replace.

hopefully this helps

 

I would say fuel pump is taking a dump.

 

Does it go up at all before it drops or does it drop straight away?

 

I'm gonna go with; needs a new fuel pump housing assembly or at least a rebuild.

1: crack in housing causing max output limit
2: bad oring sealing pressure bleedoff from filter housing. This is the oring combo on the small fitting that replaces the regulator with any proper RFS.
3: backed up internal filter. Not replaceable, requires new fuel pump housing.

 

^^^ use a Leakdown tester at 60 psi or so, and feed it into the fuel output barb of the fuel pump housing. Remove it from the tank first Incase it explodes. It should have 0 Leakdown. If it has any... That's a cracked housing or bad oring like I mentioned above. Unless the fuel pump check valve is bad, but that's not likely.

 

Also could have internal leak at the fuel pump output bushing... Which is the rubber seal that seals your walbro output barb into the fuel pump assembly.

Sorry for 3 posts but can't edit on my phone

 

Thanks for the reply's!! I really appreciate the help. Once I'm off work today I'll be trying these ideas

And for the question of if it rises at all or falls straight away. It doesn't rise at all, hovers around the set base for a second then steadily falls.

 

Hi there. It looks like I'm having the same issue as described on this thread. I had my car on the dyno 2 days ago and we couldn't maximize the power output of my LS3 due to the fuel pressure falling from 60psi down to 50psi under heavy loads. I modified my OEM fuel basket to fit the 450lph walbro fuel pump. I increased the size of the orifices on the swirly piece, as well cut off a portion of the nipple that seats on a seal. I'm wondering if that could be my culprit for the falling fuel pressure. My car is making 436whp but it's on a lean fuel curve. I'd like to resolve this so any help and advice is welcomed

 

Stock Fuel Feed?

Fuel Return?

 

It's set up as return less system. The stock LS3 fuel rail was replaced with a Holley -8AN fuel rails. A Holley fuel pressure regulator preset to 60psi is attached to one end of the fuel rails to control the pressure after it. I'm using a Sikky -6AN fuel hose from the OEM steel fuel line coming from the gas tank to the fuel rails with an Earl's in line pre-filter in between

 

Sounds like a leak in the feed line inside the tank.

 

That's what I'm thinking. I've attached a photo of the fuel pump basket nipple I trimmed to get the pump to fit.


This is the OEM fuel basket. I trimmed the top of the niplle per a DIY guide on how to install a walbro pump in the 350Z. I did all the LS swap work myself with a friend that can weld.

 

What type of hose did you use in the tank? Did you get submersible fuel line or standard fuel injection hose? Standard hose will swell and burst. I always use Gates submersible hose.

https://www.gates.com/us/en/fluid-po...-000000-000012

 

I kept the OEM hose.

I contacted ConceptZPerformance who supplied me with DIY walbro fuel pump installation I used to install my pump. They gave me this link:
https://conceptzperformance.com/blog...stem-addendum/

It's an addendum to the fuel pump write up. Looks like it might actually be the OEM wires supplying power to the pump not being able to carry enough current for operation. My tuner on the dyno suspected this as well. I need to drain the tank and get about 12 gallons of fuel out before I can work on it but, I'm going to study the write up and make a plan. I will also take your advice and upgrade the hose while I'm in there. Thanks for taking the time to reply.

 

Ah, I didn't realize you were on stock wiring. I always run a dedicated 12-Ga circuit for an upgraded pump. Use a 4-pin relay. Run a fused 12-Ga. wire directly from your battery. Use the factory pump wire to activate the relay.

 

I would look into a bigger feed line and get a return line as-well - eliminate all choke points as you can. You're only as strong as your weakest link ... and that is likely the junction from the OEM fitting on the basket to the hose line ... if I remember correctly its roughly 1/4" ... I core'd mine out a bit to get it bigger ... possibly 5/16" but not quite 3/8" ... I think this is your weak-point


I actually blew-out my OEM wiring / wiring tabs on the fuel basket when I hooked my 525 to an aftermarket relay setup. I ended up putting a hole in the fuel basket and epoxy'ing it back into place.

Post #849
https://my350z.com/forum/forced-indu...-build-17.html

 

Thanks, i8acobra for the advice. I've got to replace that wiring