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Discussion Starter #1
i am running a Ford GT intake pump. when i am in higher rpm's my fuel pressure is at 40 psi. when i get to 5800 rpm the pressure drops to 30 psi. the car made 416 rwhp at 6k. it was dropping fuel pressure on the dyno. my tuner said this pump should be good for 500rwhp. is that right? should i run an inline pump to help this in take pump? or should i just swap out the GT pump. the car also will not build fuel pressure when i 1st hit the key to prime the fuel system. i've put a manual gauge on the pressure feed line at the fuel rail and the pressure spikes, but then falls right off. i assume the pump is leaking down. this pump maybe has 3k miles. thanks
 

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Discussion Starter #3
96-97 fuel rails with stock fuel pressure reg, 60lbs injectors, return style system and i swapped to the 94-97 style tank. I got rid of the fuel delivery module setup
 

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What kind of boost are you running??? If your running stock fuel rails your likely pulling too much fuel out of the rails with the 60lb injectors. I had the same problem on my 96 cobra when i switched from 42's to 60's.
 

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Discussion Starter #5
I dont run a boost gauge, but i think on the dyno we were seeing 10 psi at 6k. The car should spin to 7k rpm. I am running a 3.33 pulley and a stock lower. Hhhmmm, i could see big injectors doing that. Any other ideas to try?
 

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I find it hard to believe that the rails would be getting drained from the 60's...There are a lot of fox body guys running 60's with factory rails making around 500 rwhp.

I'm thinking it is either pump or regulator related.

Dustin,

Have you tried priming the pump a few times to see if it will hold pressure? Maybe the check ball is failing at the pump?
 

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Discussion Starter #7
Yeah, when i hooked the mech gauge to the presure line at the fuel rail i cycled the key a few times. No go. I deffinetly think the check ball is f'ed. I also hooked the mechanical gauge to the return side of the fuel rail and i saw no presure spikes when cycling the key. I was really leaning twards a stuck open regulator like we talked about the other night. I am thinking the pump is faulty, which is crazy cause its been doing this since day one. I think the pump has like 3k miles on it
 

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I had a smiliar problem on my 89. It turned out to be my fuel pressure regulator. It wasnt holding pressure consistently and when it did it would bleed back after a few minutes
 

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Yeah, when i hooked the mech gauge to the presure line at the fuel rail i cycled the key a few times. No go. I deffinetly think the check ball is f'ed. I also hooked the mechanical gauge to the return side of the fuel rail and i saw no presure spikes when cycling the key. I was really leaning twards a stuck open regulator like we talked about the other night. I am thinking the pump is faulty, which is crazy cause its been doing this since day one. I think the pump has like 3k miles on it
Can you get your hands on a stock pump or another GT pump to test, to see if it holds pressure?
 

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I find it hard to believe that the rails would be getting drained from the 60's...There are a lot of fox body guys running 60's with factory rails making around 500 rwhp.

I am talking about factory 96-98 cobra fuel rails. I was running 15psi with the stock fuel rails using the 60's with an Aeromotive fpr and experienced the same problem. Exactly what fuel rails are you running??? The fuel pump could very well be the problem too. You need to get a boost gauge hooked up!!!!!
 

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Put a fuel gauge on the regulator and see if it holds pressure, if it doesnt its probably the regulator. Like i said earlier my 89gt had that problem last year.
 

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Discussion Starter #12
I hooked a pressure gauge up after the regulator and cycled the key and i did not have pressure. The funny thing is, i pulled the fuel pump assy out and stuck it in a can of gas and cycled the key. Fuel came out the return side of the sender. Not alot, but some did. But if the regulator was sticking open, i would have gotten a pressure reading on my gauge
 

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If the gauge is after the regulator you shouldn't see pressure as there is nothing restricting it. Put the gauge right before the regulator and see what it does. I still vote for the pump or regulator causing the issue.
 

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Macs Stang is right, mount the gauge before the regulator when trying to check the pump pressure. Your still not clear what fuel rails your using...... I can't remember how the factory stuff is arranged, but is the factory FPR a 1:1 ratio or ???? They are non adjustable correct??? I had an Aeromotive FPR on my factory rails and had to set the pressure @ 50psi with the vacuum source unhooked. It was a 1:1 ratio and gave me 60psi fuel rail pressure when i was set-up running 10lbs boost. I think your starting with the pressure too low...... Still believe your draining the rails at the pressure your running. I assume your not running an FMU either???
 

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We tested a few things last night...when priming the pump the fuel pressure gauge read zero, even after cycling the pump three times. My vote still stands as a bad regulator. The pump holds pressure when the engine is running.
 

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I am having a similar problem at the dyno with my procharged 4v setup on my 98. When it reaches 4700rpm and 480hp it starts dropping pressure. I am running a Fore dual pump setup. Looks like I am running on 1 pump and I can not tell as the previous shop wired both pumps to 1 circuit. I have asked them to wire each pump independent as it will make it easier to diagnose in the future.

As for your issue have you checked the voltage at the pump when it starts dropping? Maybe the CCRM is not providing enough voltage or you alternator is having an issue and not providing enough voltage at that rpm.
 

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Discussion Starter #18
Thats where i am at with it right now. I am gonna run a 12 ga wire back from the battery to a relay in my trunk. If that doesnt work, i am gonna replace the pump
 

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Thats where i am at with it right now. I am gonna run a 12 ga wire back from the battery to a relay in my trunk. If that doesnt work, i am gonna replace the pump
Muuuuuuuuuuuuuustang! Let me know if you need help, neighbor. :cool:
 
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