Fuel pump question

TBatt

Do any of you know if the fuel pump is a constant run type using a bypass regulator in the pump assembly. I believe it is but not 100% sure.

The reason I'm asking is the pump will run for a couple of seconds when the car is turned on and then it shuts it's self off developing only 20 psi where it should be 50+ psi. It was working fine yesterday but today when I went to start the car after work it took a long time for it to start and then it ran terrible due to the low fuel pressure (very lean). I managed to limp the car home, barely.

I have the CJM fuel gauge installed along with a AFR gauge so this is how I know it is a fuel pressure problem.

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RJM pedal, Hotchkis Sway Bars, FI TDX, FOG Light, Z1 Slotted Drilled rotors, Stillen SC, Quaife ATB, Z1 Oil cooler, AEM Gauge Set, Galeforce gauge mount, Avant Garde M590 Hypersilver w/RE-11, TopgunZ A2A kit., ECUtek tuned by Seb: ROLL TIDE!

FairladyZ40th

Bump for answers I have the same issue I believe.


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SouthArk370Z

Every centrifugal pump used to pump volatile liquids that I've seen has had a bypass/re-circulation system. If you deadhead a centrifugal pump, heat is generated in the bowl and the liquid being pumped can flash. But I've never taken an electric fuel pump apart, so I can't swear that they follow the "rule." The FSM may have an exploded drawing or you may be able to suss out the info from the piping diagrams and descriptions.

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TBatt

According to what I have read about the Walbro 255, it is a Genrotor type pump, which is a positive displacement pump and it should run all of the time letting the regulator bypass what is not needed to maintain ~55psi. The ECU starts the pump for a few seconds and then turns it off until the engine starts to turn over. This way the pump doesn't get overloaded when it doesn't need to run. This is what it is doing, coming on and then shutting off until the engine starts. So, the electronics seems to be working but the pump is not developing pressure any more. That could be the pump or the regulator. I'm waiting on a call from Stillen to see what there tech guys says.

When I first installed the new pump (part of the Stillen SC kit) the fuel pressure was around 55psi and has now dropped to 10. The engine will run but the car is not drive-able. The idle AFR was 14.4 and now it is in the 16s which is way lean due to the low fuel pressure.

I'll keep you posted on what I find.

__________________
RJM pedal, Hotchkis Sway Bars, FI TDX, FOG Light, Z1 Slotted Drilled rotors, Stillen SC, Quaife ATB, Z1 Oil cooler, AEM Gauge Set, Galeforce gauge mount, Avant Garde M590 Hypersilver w/RE-11, TopgunZ A2A kit., ECUtek tuned by Seb: ROLL TIDE!

TBatt

I did check the FSM and it really is no help. It covers removing the pump assembly and replacing it. RockAuto.com has some great pictures of the pump assembly it you want to check it out.

Getting the pump out is a real PITA. This time I'm taking the passenger seat out first.

__________________
RJM pedal, Hotchkis Sway Bars, FI TDX, FOG Light, Z1 Slotted Drilled rotors, Stillen SC, Quaife ATB, Z1 Oil cooler, AEM Gauge Set, Galeforce gauge mount, Avant Garde M590 Hypersilver w/RE-11, TopgunZ A2A kit., ECUtek tuned by Seb: ROLL TIDE!

FairladyZ40th

Idk if I'm on the same topic here, but is fuel pressure the reason the car lags at start up? I used to have engine start up with no issues just an instant "vroom" now it's laggy, very weak and forced start. Is this what you're talking about?


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TBatt

Sort of. The engine was spinning over for about twice the normal time to start. This was due to the low fuel pressure and lean start condition. The engine needs a little extra juice at start up.

If the engine is not spinning over fast you most likely have a problem with your battery. Mine was doing that early this spring. I checked the battery start voltage and saw that it was sagging indicating that the battery was weak. I installed a new battery and it was starting normal then. Have your battery checked at a local parts store. They will usually do this as a free service. If your battery is over four years old it is most likely the problem.

__________________
RJM pedal, Hotchkis Sway Bars, FI TDX, FOG Light, Z1 Slotted Drilled rotors, Stillen SC, Quaife ATB, Z1 Oil cooler, AEM Gauge Set, Galeforce gauge mount, Avant Garde M590 Hypersilver w/RE-11, TopgunZ A2A kit., ECUtek tuned by Seb: ROLL TIDE!

SouthArk370Z

Ah. I didn't realize it was a PD pump.

As you can tell, I'm no expert on car fuel systems but I do have a lot of experience with industrial pumps and control systems. The regulator would be the first thing I would check. Another possibility is the pump intake is partially blocked. If the pump motor is variable speed (I'll guess not, since it has the regulated recirc), it may not be coming up to speed. The pump itself is low on my list but always a possibility. If the recirc return line was obstructed, the pressure would be high. Low voltage at the pump (bad relay contacts, wiring is too small, cut wire, &c) could cause your symptoms - check voltage at pump motor while pump is under a load.

Hope that helps.

__________________
Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub
Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

FairladyZ40th

Thanks for that tip man I was considering the battery but never really gave it too much thought I kept focusing on the pump haha. I even purchased a 340lph walbro fuel pump but I have a NA application and feel nervous about putting that in...


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FairladyZ40th

That's actually a very nice observation! I mean if it's just bad wiring or shot circuit of some kind that is robbing power from the pump you could save your self good money and time I'm gonna stick around this thread since I'm ignorant to fuel systems, 'see if something don't stick to my brain.


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TBatt

Just got off the phone with Ivan at Stillen, he thinks the pump has failed and is sending me a new one.

I'm pretty sure the wiring and such is okay because of the way the problem got worse over time. When it first happened, the fuel pressure had dropped from 55 psi down to 40 and by the time I got home it had dropped to around 15. Sure sounds like the pump motor was giving out or something was progressively clogging up.

I will need to partially drain the fuel tank. When the tank is full, the fuel level is above the opening for the pump and it will spill out. The FSM says that I will need to drain about 4 gallons out from full. I plan on attaching a hose to the output fitting and let the pump drain the fuel into a gas can. I will be sending power through the pump connector so I can have it run without the engine running because the engine won't run without fuel. It the engine isn't running, the ECU turns off power to the pump.

It could be a regulator problem like you stated. I sure hope not because the regulator is not sold separate from the pump assembly and the whole pump costs $500. Ouch!

__________________
RJM pedal, Hotchkis Sway Bars, FI TDX, FOG Light, Z1 Slotted Drilled rotors, Stillen SC, Quaife ATB, Z1 Oil cooler, AEM Gauge Set, Galeforce gauge mount, Avant Garde M590 Hypersilver w/RE-11, TopgunZ A2A kit., ECUtek tuned by Seb: ROLL TIDE!

FairladyZ40th

So you have a 255lph pump and still require a regulator? I was told I'd be ok without a regulator using a 340lph pump


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TBatt

The fuel pressure regulator is part of the fuel pump assembly. It is built in.

I would NOT change the pump from the stock setup unless you are going to forced induction (turbo or supercharger). It is a real pain to swap out and you just don't need that much flow with a stock setup.

Most of the guys I have seen using the 340 and up are also using a return line fuel system and those guys are running lots of boost and or E85. The 255 Walbro pump is good up to 450-500hp. Beyond that you will need to go to the 340. If you run E85 and high boost you will need the 450.

__________________
RJM pedal, Hotchkis Sway Bars, FI TDX, FOG Light, Z1 Slotted Drilled rotors, Stillen SC, Quaife ATB, Z1 Oil cooler, AEM Gauge Set, Galeforce gauge mount, Avant Garde M590 Hypersilver w/RE-11, TopgunZ A2A kit., ECUtek tuned by Seb: ROLL TIDE!

FairladyZ40th

Well I was considering on doing the e85 conversion but staying NA for a while. At least till I can get some cash to pull of a TT or SC kit. I'd like to stay as stock as possible and whoop a$$, feel me?


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TBatt

All I can say is to plan ahead and do your research on what direction to go. I've been planning (and saving) for six months, reading every post I can find.

Some of the kits are very complete and some are not. I don't think that any TT or SC kit includes a pump or injectors that will support E85 so you will need to research that aspect. Big injectors (+1000cc) and a high volume pump will be needed such as the 340 or 450 depending on your target HP.

What I did was to set a target HP and then find the best bang for the buck. The stock Stillen SC kit is very complete but it also has a 400-420 rwhp limit. I wanted 450 so I looked into the air to air kit that Topgunz was working on and it looked like it would give me what I was after. The dyno results from the prototypes looked good and were getting into the 450 range. A single turbo could have done the same but I wanted the linear hp pull that a SC has. You always know where the HP is because the SC is directly driven by the engine and has very predictable power which is very important when you are pushing the car at or near it's limits in a curve. Turbos are load driven and can supply boost in a non-predictable way when compared to SC.

Anyway, the parts I need are on the way and all should be here by Thursday. Till then I will drain the fuel tank partially and take the passengers seat out and start removing the pump assembly. I won't take it out until the new pump is here because I don't want to leave the gas tank open and smell the garage and house up.

__________________
RJM pedal, Hotchkis Sway Bars, FI TDX, FOG Light, Z1 Slotted Drilled rotors, Stillen SC, Quaife ATB, Z1 Oil cooler, AEM Gauge Set, Galeforce gauge mount, Avant Garde M590 Hypersilver w/RE-11, TopgunZ A2A kit., ECUtek tuned by Seb: ROLL TIDE!