Well I have an 03 GT Hardtop. Mods include a MAC straight shot intake, UPR offroad X Pipe, Flowmaster cat back, Steeda Pulleys, ZEX wet nitrous system, Nitto Drag radials, Pro 5.0 shifter, and a Walbro 255 fuel pump.

Since I had the fuel pump installed the fuel system is overpowered running around 45 psi. This kills my top end so its really embarrasing trying to race it right now. The shop I go to said I need a custom tune with the returnless fuel system to fix it.

So 3:73 Gears Or the tune????

 

well your first problem is that walbro doesnt make a returnless fuel pump for our cars 99-05 so you got the wrong fuel pump and it needs to come out asap.
2ndly if it was me i would dyno tune it to get the most out of your nitrous and mods.

 

if it was me i would get a new fuel pump, then put in the gears, then get a tune. If you do it the other way, your going to need to get your car tuned anyway after the gears, so why waste the time and money doing it twice?

 

I kinda agree, because you dont HAVE to tune your car for gears, you could just buy a speedcal, but if you can wait, save for the gears and tune at the same time. But, change the fuel pump out asap as Spike said. The focus pumps are supposedly pretty good.

 

As said before get the walbo out now. I dont know who sold it to you or told you it would work properly but I would bitch at them.

Get a Focus or Aviator fuel pump, buy the gears, and then tune it.

 

I think we covered the fuel pump part. As for the tune or gears. get an SCT chip and just have them put 2 tunes on it, one for stock gears and another for your 3.73's or whatever.

 

OK, I dont get it. Im not saying I dont believe you guys but, How do I have the wrong fuel pump? I know 2 other guys with returnless fuel systems using the same pump. Delk Performance sold it to me and they recommended it for my car. Since they have worked on fuel systems for countless 03 cobras and returnless style GTs I went with it instead of a focus. I just dont see the difference between the two. The walbro looks exactly like the stocker except its bigger, and theres only a positive and a negative wire that connects to it. It even uses the stock sock on the end of it.Sure the car doesnt run well now because the pump is putting out 45 psi at idle instead of the stock 39 psi. Since the cars computer controls the fuel pressure the big pump is running at the same speed as the smaller one so it makes more pressure in the system. So its not the pump itself, it is the fact that the computer doesnt know theres a big pump in there and a custom tune will fix that.

Maybe Im wrong. Fill me in.

 

the fuel pressure unit on the fuel rail reads fuel psi and adjust the pump voltage accordigly like i said walbro doesnt make a returnless fuel pump for our cars. I have heard of other people getting the same problem as you. it happens. and even an aftermarket larger pump like the focus the car will just just as it did before. meaning the computer adjust the voltage to the pump. the reason for the other pump is to extend the amount of fuel it can push. so the focus will push high 30's at idle like the stocker becuase the computer is regulating the voltage. I hope this makes sence its been a long day with school.

 

I dont see why youd need a tune when putting in a new pump. You dont need a tune after installing a focus or cobra pumps. I have been told that its normal to have higher psi at idle during hot weather because the fuel is being sent faster so it doesnt boil in the lines. Ive seen my psi go up to 50 at idle while sitting in heavy traffic.

 

go to www.modularpowerhouse.com and go to the forum and ask about the walbro fuel pump.

As said above the adjustable voltage the pump is send will burn up the walbro as it was not designed for that.