05 Gt fuel pressure dips

Justin302

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This happens at almost ANY rpm and the fuel pressure gradually increases as the rpms climb in wot. When it the fuel pressure dips to 32psi right off the bat the fuel pressure duty cycle is at .31 and when the fuel pressure gets to 38psi the fpdc is at .40. I just installed a new fuel pressure sensor with no change.

I have an Eforce blower, gt500 pump.
 

Pentalab

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The GT-500 pump is a dual pump.

I have a single pump on my 2010 with Roush M90 blower. With key on, eng OFF, fuel rail pressure is 50 psi. With eng on, whether idle or wot, it's 40 psi. FPDC (fuel pump duty cycle) is 40% at idle....and 80% at 6.2 krpm, gas pedal mashed, blower on, max boost.... 5.8 psi.

One day, the eng would gag.... but only when trying to get into boost.... IE: would gag when boost gauge hit 0 psi. Fuel rail pressure would drop to 5 psi ! FPDC went up to 98%. Problem was a clogged sock filter, on bottom of fuel pump. Pump removed, sock removed and cleaned out with garden hose, dried, re-installed. Problem solved.
 
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07 Boss

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This happens at almost ANY rpm and the fuel pressure gradually increases as the rpms climb in wot. When it the fuel pressure dips to 32psi right off the bat the fuel pressure duty cycle is at .31 and when the fuel pressure gets to 38psi the fpdc is at .40. I just installed a new fuel pressure sensor with no change.

I have an Eforce blower, gt500 pump.


I'm having a hard time understanding the issue. Fuel pressure should increase with manifold pressure not rpm's. Fuel pressure should remain at a constant pressure above manifold pressure or vacuum. So at a given manifold pressure or boost level, the fuel pressure should remain constant with the duty cycle increasing as the rpm's increase. So you will have different duty cycles for a given pressure at different rpm's.

But let me see if I can decipher this. When you step on the gas the pressure drops to 32. As the rpm's increase pressure increases to 38 psi. How much boost are you running when the pressure is at 38 psi?
 

Justin302

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The boost is 12psi. And even low rpms like 2k where no alot of fuel is needed it still dips the fuel psi ro about 32psi. My fuel pump is real new like 2k miles and the fuel filter was done at the same time.
 

Pentalab

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Is the ..'sock' on the bottom of the fuel pump clean ? If not, your pressure will drop off.
 

07 Boss

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So the pump is new, why was it need of replacing? Did this pressure issue start then or did it run fine for a while? What I find a bit odd is that if the proper commanded fuel pressure is not met, wouldn't the ecm increase pump duty cycle until it got the pressure to where it was supposed to be. I'm curious as to what the fuel pressure does in relation to boost and what ecm is telling the pumps to do. I suppose you have already checked out both fuel modules and made sure power was getting sent to both the motors.
 

Midlife Crises

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I just went through a wrestling match with the GT500 Pumps in my 2010 GT. Lag in response, .3+ duty cycle while idling and a few psi low fuel pressure. In my case fuel pressure would never increase. Turned out I was only running on one pump. Replaced both pumps and still had intermittent duty cycles, voltages and pressure. When I fixed the loose wire connections at the fuel pump hat and the FPDMs all the problems went away.
 

Justin302

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This is a new build with a freshly forged motor. The original owner has died and the car ran pretty good (580 whp). It always had a lag tho when you first hit the pedal and was lean at first too. I decided to have LaSota tune it and he saw the fuel psi drop at first too. I am trying to get that fixed so I can get my car on the road. I am all out of ideas tho....
 

Midlife Crises

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When I repaired the bad connections my pump duty cycle dropped to .17 while idling with 39 psi. Bad connections loose voltage.
I am sure I created some of the connection problems myself by pocking a multimeter probe into the sockets during the build. Look for spread sockets that may not grip the pins. My biggest offender was the command wire to the second FPDM and a black wire at the pump hat.
 

Justin302

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I will check my connections. I did unplug each fuel pump one at a time to see if one pump was failed, they both are operational.
 

Justin302

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I checked all my connections and everything looks good. Any guesses would be appreciated, thanks!
 

Justin302

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Edelbrock Eforce tech support seemed to think that is normal, wonder if they are right?
 

07 Boss

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I will check my connections. I did unplug each fuel pump one at a time to see if one pump was failed, they both are operational.

They might be running but are they pumping what they should? You gotta time and measure to check actual flow to completely rule out the pumps.
 

07 Boss

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Edelbrock Eforce tech support seemed to think that is normal, wonder if they are right?

There's always going to be a slight drop but it should be almost undetectable. The concern is the amount of time it takes to get back to where it should. It should be almost instantaneous in recovery.
 

JeremyH

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OP based on your original post I see no issue. Pressure should be 30ish under vac, is there a afr issue? What is the root problem you are trying to solve?
 

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