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Old 05-27-2012, 10:01 PM   #1
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Car: 1989 Iroc Z 5.7L
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Fuel Pressure

Got a 1989 iroc z with a 350 tpi. Right after I bought the car one of the injectors went bad and a few were weak so I got some 24lb injectors from summit and a custom tune. Car was running great with about 50psi at the rail, then the fuel pump started getting weak. Finally got a racetronix wiring kit and 255 walbro pump installed but only getting 24psi to the fuel rail. It seems to run fine but the pressure does not make sense. Anyone else running a 255 fuel pump and 24lb injector combo, what is your pressure to the fuel rail?
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TPI STREET Performance

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Old 05-27-2012, 10:42 PM   #2
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Car: 91' Firebird SOLD
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Re: Fuel Pressure

Quote:
Originally Posted by rwstegne View Post
Got a 1989 iroc z with a 350 tpi. Right after I bought the car one of the injectors went bad and a few were weak so I got some 24lb injectors from summit and a custom tune. Car was running great with about 50psi at the rail, then the fuel pump started getting weak. Finally got a racetronix wiring kit and 255 walbro pump installed but only getting 24psi to the fuel rail. It seems to run fine but the pressure does not make sense. Anyone else running a 255 fuel pump and 24lb injector combo, what is your pressure to the fuel rail?
Pressure as high as that is hard on the fuel pump. Stock pressure for a 350 tpi is 43.5 psi.
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Old 05-28-2012, 11:22 PM   #3
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Join Date: Nov 2010
Location: Raleigh
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Car: 1989 Iroc Z 5.7L
Engine: 5.7L
Transmission: auto 700R soon T56
Axle/Gears: built 3.08 10 bolt Locker

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Re: Fuel Pressure

I have the GM service manauls and hans manual so I knew the 43.5 psi to the fuel rail. I am trying to figure out how I went from 24lb injectors and original fuel pump at 50 psi to today situation of 24lb injectors and a 255 fuel pump with only 24 psi ish to the rails. What am I missing?
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Old 05-28-2012, 11:34 PM   #4
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Car: 91' Firebird SOLD
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Re: Fuel Pressure

Quote:
Originally Posted by rwstegne View Post
I have the GM service manauls and hans manual so I knew the 43.5 psi to the fuel rail. I am trying to figure out how I went from 24lb injectors and original fuel pump at 50 psi to today situation of 24lb injectors and a 255 fuel pump with only 24 psi ish to the rails. What am I missing?
If u are running 24lb injectors then it is going to run overly rich. You would need to turn down fuel pressure about a pound and a half from stock to get it to run somewhat normal. Yes, stock is 43.5 psi.Now if you are running 24 lb inj at 43.5 psi then that is just like running the stock injectors (22lb) at 50 psi. Too much fuel pressure and u lose power and it is also hard on the pump.
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Old 05-28-2012, 11:38 PM   #5
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Re: Fuel Pressure

Trying to run 24lb inj at 50 psi is way too high. Try 42psi with inj that big! Sounds like u need to get a custom tune now to adjust for those 24 lb injectors,so it can perform like u have 22 lb injectors in there. Yes, try 42 psi fuel pressure and it should run better.
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Old 05-28-2012, 11:40 PM   #6
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Re: Fuel Pressure

im surprised your car even started with inj that big and running 50psi of fuel pressure! How bad was ur pump whining?
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Old 05-29-2012, 06:54 PM   #7
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Re: Fuel Pressure

fuel pressure is set with car idling,vacuum hose disconnected and plugged ,manifold nipple plugged. This simulates WOT.
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Old 05-29-2012, 06:54 PM
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