Fuel pressure issue

[MercuryLs]

So I'm having an issue with my fuel pressure. I have a built DOHC 4.6, Vortech V2 Si (3.1 blower pulley, IW 7.75 Crank pulley), Stock 1997 Cobra fuel rails, Stock fuel lines (return style), 80lb Injectors, TWIN in-tank 255lph fuel pumps.

This is what it is doing>
-Base fuel pressure is 41.
-It drops into the 30s under vaccum, When I get into boost (close to 10psi) the fuel pressure rises to 50-52psi than falls FAST down to 35psi.
So my car goes LEAN BAD as soon as it starts to come into power.

-I checked both pumps, they both are working.
-I pulled the pumps out to check the lines, and that is all good as well.
-My fuel filter & Fuel Pressure Regulator (stock) is new.
-Voltage is consistent
-I can not find any kinks in the line, although I do need to trace them all the way from the tank to the rails to be 100% sure.


There has got to be NO WAY im am exceeding (in HP terms) my fuel systems capacity . :shrug:

 

[sunburned]

Try upgrading the fuel lines. I had a similar issue with my car when I installed dual walbro pumps. In my case, the fuel pressure would not go below 50psi, even at idle. Turned out the return line was just too small for the amount of fuel the pumps were putting out. Ended up going to a FORE hat and AN lines, -8 feed and -6 return. Hooked up to the stock rails and worked perfectly. However, you really can't have ANY of the stock sized lines because they will create a bottleneck in the system and screw with the pressure.

How exactly did you mod your fuel hat to fit dual walbros? Are they both in tank or is one inline? Mine ran in parallel, both in tank, so it was pushing a ton of fuel.


Looks like Lethal has '03 Cobra tanks for $328 and then you can get the dual Walbro FORE hat setup for return style systems. This will let you hook up the AN lines very easily. Adapters from AN to the stock rails are available through JEGS I believe.

http://www.lethalperformance.com/96...04-cobra-fuel-tank-fuel-pump-assembly-p-30501
http://www.lethalperformance.com/03...-04-cobra-dual-walbro-pump-billet-hat-p-17794

http://www.jegs.com/i/Russell/799/640880/10002/-1
http://www.jegs.com/i/Russell/799/640870/10002/-1

 

[MercuryLs]

Well it's actually in my Lincoln, and I modified the hanger to hold two pumps and y-together into the factory line. I'm returning fuel just fine, my pressure is at 42 base and drops to 30s in vac.

 

[sunburned]

Well, there are only so many things it could be. Maybe the new regulator is faulty? i think with all that fuel flowing and all that power, I'd be running something aftermarket that's made for it.

Check two threads above for the FORE precision FPR.

 

[TheShadow]

Measure the diameter of the supply line. In the Mustangs anyway, Ford used 3 different sized lines, with no apparent reason. 1/4", 5/16", and 3/8". I found that my 94 Cobra had 1/4". You'll run out of fuel at around 350-370 rwhp, in my experience. I saw the exact same thing; lean a/f and a serious drop on fuel pressure measured at the rail. Hope this helps!