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Old 01-04-2018, 08:51 AM   #1
spotamiss
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fuel pressure problem

having trouble with fuel pressure on my 03 mach 1. at idle, its only 15-18 lbs. I have changed everything in the fuel system. new fuel pump, it's an aeromotive 325 lph pump, I have a Kenne Bell boost-a-pump set to 25%, new fuel filter, new FPDM, new FIPS, AND STILL only 15-18 lbs at idle. My vacuum is 21 1/2 inches at the FIPS, and I'm getting 5.1 volts to it. if I disconnect the harness to the FIPS, vacuum increased to 22 inches and fuel pressure goes to 40. any ideas ?
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Old 01-04-2018, 09:06 AM   #2
01yellerCobra
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How are you measuring fuel pressure? Is the car running bad? Returnless set ups will change more than a return style.

The FRPS maintains a 39-40psi drop across the injectors. Meaning the pressure in the rail is about 40psi higher than what would be at the outlet of the injectors. Easiest way to think about it is if you have 10psi of boost going into the engine, then fuel pressure would need to be 50psi at the fuel rail to maintain the 40psi difference. When the engine is in vacuum it doesn't need as much pressure. So the 21.5" can be thought of as negative. 21.5+19=40.5. Of course I'm using absolute values. But going by that math your pressure is correct.

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Old 01-04-2018, 09:40 AM   #3
spotamiss
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Re: fuel pressure problem

I have a electric fuel pressure gauge, it's an autometer. it takes fuel pressure at the fuel rail, passenger side. it is supercharged, and I have all the supporting pieces, 42lb injectors, bigger MAF, 65mm throttle body.
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Old 01-04-2018, 09:47 AM   #4
spotamiss
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Re: fuel pressure problem

and the pressure doesen't go up when I'm driving. stays just under 20psi. I had it on the dyno, and the shop that I use told me that my fuel pump was bad. it was breaking up when it would go past 3500-4000 rpm. which was when the boost would start. it's a procharger p1sc ho kit. 10 psi.
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Old 01-04-2018, 09:50 AM   #5
spotamiss
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Re: fuel pressure problem

it threw a p0190 code, so I'm going to replace the sensor(again)
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Old 01-04-2018, 10:31 AM   #6
01yellerCobra
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Check your pressure across the injectors. If you're blowing the FRPS that fast I'd say the tune still needs work. That should be plenty of fuel for your set up.

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Old 01-04-2018, 10:52 AM   #7
spotamiss
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Re: fuel pressure problem

gonna give it a shot, and lets see what happens. wish me luck, and thank you for the advice.
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