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Discussion Starter #1
We are currently tuning my 2001 Vortech Cobra, everything is going Very well EXCEPT the fuel pressure. i have a Walbro 255 in-tank pump and a kenne bell boost-a-pump. my gauge shows 55psi all the way to 6k then fuel pressure drops to 20-25 psi. whats goin gon here? we have played with basically EVERYTHING. with no luck....whats the deal???

thanks Jason
 

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How or who is tuning your car? What is meant by tuning? ie chip tuning on a dyno and laptop or mechanical under the hood stuff in the driveway.

Any dataloggers on car? That's probably the best way to figure it out.

I really hope it works out, I am not doing the blower until the steeda or 03 cobra pump is out and ready.

Best of luck and please keep us posted on progress and results.
 

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Discussion Starter #4
The fuel canister IS modified, there is a 9/16 hole in the front of it to promote fuel flow.

There is a VERY well known installer/tuner here in michigan doing my install and tune. we are using 2 laptops (one running monitoring in real-time, on edoing the changes, and a wideband) the car was dyno tuned AND is being tuned on the street

Jason
 

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Discussion Starter #6
well its wierd i think it MAY be hidden somewhere in teh software. but we dropped the tank today and put a new pump in it justin case, didn't help.

J
 

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just a thought but the pcm monitors the fuel rail pressure, it keeps the fuel pressure at a steady lets say 40psi by duty cycling the pump in the tank. so if you have external pump raming fuel up to the rail constantly the pcm will probably try to reduce the pressure to get it to it's normal range! since it can't adjust the external pump it's going to adj. the pump in the tank. it could duty cycle the pump down so low it's not feeding your secondary pump! jmho. i would try to run just the pump in the tank and see what it does! good luck.
 

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Discussion Starter #8
the boost a pump doesn't move fuel, all it does is send extra voltage to the intank pump tomake it work harder. Would aftermarket fuel rails fix anything?


J
 

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What does the tuner/installer say?

Seems like this would not be a new issue. Obviously you have already checked the normal things. But now it seems you are in the stage of second guessing and looking to add more parts. I've been there and done that. Sometimes it works and sometimes it doesn't.

Personally, I wouldn't add parts yet, because most likely your system as it sits has worked on other identical cars. I am not saying adding parts won't help or is not good, but you may be masking the real problem.

You are seeing the fuel pressure through the laptop, not gauge, correct? I know I had trouble with my electric fuel gauge, autometer replaced it no problem. just a thought.

Again, keep us posted becuase this is interesting and good luck.
 

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stradt14 said:
The fuel canister IS modified, there is a 9/16 hole in the front of it to promote fuel flow.

There is a VERY well known installer/tuner here in michigan doing my install and tune. we are using 2 laptops (one running monitoring in real-time, on edoing the changes, and a wideband) the car was dyno tuned AND is being tuned on the street

Jason
Who's doing it? Thanks Ron
 

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Discussion Starter #11
no we are watching the fuel pressure through a Autometer full sweep gauge. it SEEMS to be very accurate.

We dropped the tank again today and noticed soemthing sort of odd. The rubber thing on the top of the pump had a few small fractures in the rings of it. (sorry crappy description).

Ther fuel pressure is at 50 psi at WOT (3k-4.5k) then when i hit 4# of boost the boost-a-pump kicks in and shoots the pressure to 80 psi. After the initial "boost" from the boost-a-pump the pressure drops off to 20-25 psi.

could it be the computer pulling voltage from the pump?

oh we are using Autotap v.2

Jason
 

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What happens without BAP? Or have you tried just wiring BAP constant (no Hobbs switch) at say 0% (which makes sure pump gets 12V) or at 10% constant. A 255 hi pressure by itself should be enough for 400-450 RW in a return system. Not sure about returnless system. Don't see how changing rails would help.
 

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If you cannot figure out hte problem> It might be worth it to convert to return style fuel system. I converted about a year ago and it is MUCH better. I was told that when that pressure spikes like you desribe that you may blow the sensor inside the fuel rail or the fuel rails themselves> if you only see 80psi. spike then you should be ok> Does your gauge bounce at all when you drive the car? Returnless systems usually do> and it was very annoying for me. You can use the factory rails> just have to weld on a plug ont the end of the left rail> you can see some pictures here www.98cobra.com if you would like. Click on Harold 99cobra and you can check it out. Lidio at alternative auto has had some good luck with these boost a pumps> you might want to try him? What Vortech blower are you pushing> an S trim or the E trim? The return style fuel system is definately better when dealing with a supercharged motor.
Hope this helps :D
 

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Discussion Starter #14
I am dealing with Lidio. when we run without the BAP the pressure hangsout around 50 psi with NO spike to 80 psi then it drops as usual to the 20-25 psi.

about how much money is involved in converting to a return style fuel system? trying to keep costs down (I just turned 20, still have college tuition PLUS saving for a built block)

J
 

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Which Walbro pump are we talking about (GSS317 or 342)? What kind of power level are you seeing? I see similar effects in my car with no BAP. FP spikes up to ~55 psi then at about 5500, it starts to drop. Fortunately, Im shutting it down around 6000 so the a/f stays rich until then.

My suggestion would be to change out the fuel lines. I also am interested in someone (besides me) trying out Steeda's duel pump.

good luck.
 

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stradt14 said:
I am dealing with Lidio. when we run without the BAP the pressure hangsout around 50 psi with NO spike to 80 psi then it drops as usual to the 20-25 psi.

about how much money is involved in converting to a return style fuel system? trying to keep costs down (I just turned 20, still have college tuition PLUS saving for a built block)

J
PM Coop before you go returnless. I would think that the computer is seeing the 80psi and is trying to reduce it to "normal" range. The returnless uses a varible voltage fuel pump, but I think the boost a pump is messing up the voltage/pressure function that the computer expects. I would think that a inline pump would be better, because it would not increase the pressure but would help increase the flow.
 

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Coop99cobra still has returnless style fuel system> and is making I think 570rwhp.........problem is> with returnless he cannot get any more fuel to make more power> from the last time that I talked to him that is what he told me. For that power level its great> but NOT if you are 20 years old and yearning for more power! LOL > if you build a new motor and throw more boost at it> you're gonna need to go with a return style fuel sytem in the future> all depends on how fast you want to go.
I have the same yearning to go fast> just about to turn 24 years old. Lidio knows his ****> but I think you may need to decide how far you really want to take your car? Its gonna be much cheaper building an older mustang> these modular motors are not cheap.....but> if you like your car> you're going to have to step up to the plate :D The return style fuel system will probably set you back close to $2000. Cooptried running some larger injectors> I think they were 50's> but they went static on him because of the HIGH fuel pressure of the BAP> he had to go back down to the 42's to make that kind of power. Do you get a bouncing fuel gauge? I used to> hated it!
Hope this helps you out bud! :D
 

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Discussion Starter #18
actually, my FP gauge is pretty constant. It does a little bounce when you stomp on it, but it recovers in a blinck of an eye. Other than this little blip it is very smooth. I will EVENTUALLY build the motor, this winter probably.

As for the 80 psi theory, the BAP is adjustable, we started with having it shoot the FP from 50 up to 60, it would still drop, so i think we can rule out the BAP sending too much voltage.


I believe that it is the Walbro 317

Does anyone know if i can run a inline pump as well as the BAP and the big intank one?


thanks Jason
 

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I was thinking of going returnless also but I want to see what kind of fuel setup the 03 Cobra has. I'm guessing the injectors are 42 pounds since I read somewhere that the mass air meter is the same as the lightnings. Does anyone know if the Lightning has the returnless style fuel system?
 

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Discussion Starter #20
i don't think going to bigger lines will solve the problem, i think it is a voltage problem TO the intank pump.

any other ideas?

J
 
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