fuel pressure dropping

ruiz83

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so i took my car to get dyne tuned, they called me and said i didn't have enough fuel :shrug: on the dyno the pressure would start at 60psi at 3k-ish then drop while rpm's were climbing ( 4k 50psi, 5k 40psi and 6k-sih 30psi). i could actually hear where the engine was struggling to climb rpm. i have stock fuel rails that are hooked up to a fore innovation pressure regulator and fore innovation fuel hat. i would think this is enough fuel, the tuner told me that it could be my fuel rails or a bad pump....im leaning towards a bad pump.

here is my question, how much fuel pressure will the stock 03 cobra fuel rails hold before needing aftermarket fuel rails? how can i test the flow on a fuel pump?

- e85 fuel
- 2 walbro 450lpm pump
- kb boost a pump
- ported eaton
- 2.76/4lb lower
- 80lb injectors
- sct ba2600
- accufab plenum and tb

thanks in advance
 

MG0h3

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Its not the rails holding pressure, its the volume that they can flow. So if your engine is consuming enough fuel to essentially drain the rails (not literally but enough to lower pressure) you could see the pressure drop. Many run stock rails up north of 700rwhp so I dont think that is your issue.

What is your feed line setup? Id start with checking your fuel filter. Some hat/pump combos dont fit the tank correctly and the sock could be buried into the bottom of the tank.
 

98 Saleen Cobra

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Why is your base pressure at 60psi on the regulator? That seems really high. Most regulators are boost referenced. It should be like 39 with the vacuum off. Then go up 1psi for every 1psi of boost. IDK seems weird there for 1.

2. it kind of sounds like you have a pump going bad.. BUT two 450's and a damn BAP should support a ton of power regardless. Is it a full return fuel system?
 

c6zhombre

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it's not the fuel rails...you're not even close combo wise to having the factory rails be the bottle neck point
 

JeremyH

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May also be an issue with the setup. Sounds like your regulator is pre rails so going to a dead on the rails. How is the regulator (what ports etc) setup and is vac/boost referenced? How far away is the regulator from the rails and what are the line sizes.
 

JeremyH

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Also you listed two 450 pumps and a bap? Get rid of the bap 2 450s will do 1000rwhp on e85 in return that's a lot of voltage and current your putting to the pumps, they already pull about double the current of a 255 pump so that will wear them faster and suffer high temp flow losses. Also how is all wired and what size wire. Wiring to pumps that big is overlooked so much and makes a big impact on pump performance. 600-700rwp range is where you want to consider rails and pass though regulation ie regulator after rails. Much more optimal setup and the fuel is forced through the rails so no chance in the rails getting starved. When setup properly you can get to 700-800hp range dead heading to the stock rails but some data for you, on a 650rwhp e85 setup we got 26% flow back going to Fore rails and 8an line throughout.
 

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