fuel pressure ? - MustangForums.com


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Old 07-03-2007, 06:16 PM   #1  
bighungrymatt
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Default fuel pressure ?

After I upgraded my fuel pump last weekend, I noticed on my autometer fuel pressure gauge that when i turn the key to on the pressure will go to 30psi and then slowly drop close to zero. But if I start my car right when it gets to 30psi it will stay there. I never had this problem before I put in my 255lph fuel pump.
What do you guys think the problem is?
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Old 07-03-2007, 06:30 PM   #2  
7upedition
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Default RE: fuel pressure ?

Are you saying that when the pump primes the gauge jumps to 30 and then slowing recedes, and once you turn the car over the pump stays at 30 psi? By the way that pressure is low... should be 32-38psi.
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Old 07-03-2007, 06:45 PM   #3  
bighungrymatt
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Default RE: fuel pressure ?

yeah it jumps to 30 then slowly recedes... and if i turn the car over it will stay at 30psi

yeah I was thinking it was kinda low, but thats what my tuner set it at when he tuned my s/c
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Old 07-03-2007, 06:47 PM   #4  
7upedition
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Default RE: fuel pressure ?

wow.. what size injectors are you running, what your a/f ratio with boost?
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Old 07-03-2007, 06:53 PM   #5  
bighungrymatt
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Default RE: fuel pressure ?

I have 24# injectors. While in boost I am at 12.2 a/f ratio
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Old 07-03-2007, 06:56 PM   #6  
LTnone
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Default RE: fuel pressure ?

When you turn the key w/o cranking, the pump pumps fuel into the lines, and therefore creates pressure. If it remains off, the pressure will dissapate slowly. Try a pressure of ~38psi w/ vacuum disconnected and plugged
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Old 07-03-2007, 06:59 PM   #7  
bighungrymatt
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Default RE: fuel pressure ?

ok I will give that a try, I was just puzzled because i didnt recall seeing that happen on my stock fuel pump
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Old 07-03-2007, 07:04 PM   #8  
Joel5.0
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Default RE: fuel pressure ?

Leakdown problem.....pressure drop should not exceed 5 psi in 60 seconds....and 30 psi is the minimum OEM acceptable pressure spec.....when you say "thats what my tuner set it at when he tuned my s/c"....do you have a tuned chip installed?
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Old 07-03-2007, 07:18 PM   #9  
bighungrymatt
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Default RE: fuel pressure ?

no tune chip... the tuner adjusted my kirban fpr and my fmu and that is what the fuel pressure ended up at...

so you think I have a leak?
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Old 07-03-2007, 07:23 PM   #10  
mattdel
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Default RE: fuel pressure ?

so you paid someone to tune your car, without a custom chip.
he just dialed in your fuel pressure, 9 psi lower than stock? and your A/F shows leaning on the rich side?
with 24# and boosted?

im lost
i'm aparently missing something

anywho, yah. leakdown problem. i suppose you didn't replace the included hose when you installed the pump?
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