Fuel pressure... - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 5 Old 11-14-2013, 03:54 PM Thread Starter
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Fuel pressure...

Another newb question...

What does everyone set their initial fuel pressure to? I was thinking 43.5 was the standard, but this is a turbocharged E85 application. So does this impact the initial setting at all? I have a rising rate regulator that should compensate for the boost and 160lb injectors.

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post #2 of 5 Old 11-21-2013, 01:25 PM
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There is no standard for your application. You didn't say what year vehicle you have.
43.5 is a good starting point. All FPR's are rising rate, even the factory one. The rate is 1:1, add 1psi of fuel pressure for every 1 psi of boost.
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So many people get this wrong (not saying you), here it is, directly from the Ford 1988 Car Shop Manual

Ford specifies the following in the Shop Manual for 5.0L SEFI HO (p. 24-35-7)
Engine Running: 30-45 psi (i.e. vacuum line attached)
Engine Off (Ignition On, Pump On): 35-45 psi (i.e. no vacuum line attached)
Ford also says: Balancing one side of the fuel pressure regulator diaphragm with manifold pressure maintains a constant fuel pressure drop across the injectors.
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Convert manifold vacuum to psi
20 inHg (inches of Mercury) vacuum = 9.8 psia (about 10 psia, pounds per square inch absolute pressure)
10 inHg (inches of Mercury) vacuum = 4.9 psia (about 5 psia, pounds per square inch absolute pressure)
Ford spec allows for a 5 psia drop, since manifold vacuum can vary.

40 psi is the generally accepted value with line on. Pulling the line generally goes to 35 psi. Most all FPR's won't go below 35 psi, line on or off.


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post #3 of 5 Old 12-17-2013, 08:25 PM Thread Starter
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Thanks for the info! I should have given you some specifics. 72 Maverick with a 347 that is turbocharged with E85. I ran a carb setup for about a year, but I decided to go FI for consistency. I have the Aeromotive regulator for FI (boost referenced) now and the Aeromotive Pro pump. 160lb injectors (just had them flowed) and I am running an MS3 pro. I expect around 800-1000hp from this combination (of course that could be argued).
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post #4 of 5 Old 12-19-2013, 03:59 PM
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I would start at 43.5 as Blown88gt said.

keep in mind you can adjust your pulsewidth to deliver the correct amont of fuel with your ecu IMHO (H is very humble in this case) changing fuel pressure is a trick to use when you can't adjust injector pulsewidths when your injectors are too little or little to big .

However i can see in some cases when you have a good motor (like the one you said) having trouble at idle becuase the pulsewidth can only go so small (this is theory), you'd lower the pressure a tiny bit, the injector has to remain open a tiny bit longer to get the same fuel .

Fuel pressure isn't as critical with an aftermarket ECU. You want it to be in the range of coarse and the post above give what you should start with. The pulsewidth part of the VE number is releated to fuel pressure.

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post #5 of 5 Old 01-07-2014, 05:33 PM Thread Starter
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Thanks for the input! I will be setting it up and we shall see what happens this weekend.
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