fuel pressure issues

[mustang98gt]

I greatly appriciate any assistance in this matter: I own a 1998 Mustang GT 4.6 liter (manual). I have just installed a Walbro GSS3017 255lph fuel pump after my stock fuel pump started to fail (loss of 6psi and going). Since installing the pump and sealing it all back up, I immediately noticed problems with engine performance while driving. It would start to 'buck' wildly at just above idle speed and through a small portion of accelerating up to WOT. Pressure at the schrader valve was 90 to 100psi!

I looked at my 1998 Mustang GT to replace the apparent (to me) faulty fuel pressure regulator attached to the fuel rail / fuel injection supply manifold, while looking at a Chilton's and Haynes car manual. Wouldn't you know it, the 1998's are different than the 1996/97 4.6 liters. The 96 and 97 you can replace the regulator by detaching it with an allen tool. The 98 is WELDED to the fuel rail!

I have replaced successfully the 98 fuel rail with a 97 ford crown vic police car fuel rail and added a BBK1707. I adjusted the regulator far down as it would go like the instructions said. The best I can get it down to is 65 PSI. The voltage at the pump is 12.5 volts. Both the Haynes and Chilton's manuals say the voltage is suppost to be 10.5 volts. Right now my car runs okay but it still bucks somewhat at just above idle speed. I had a full tank of gas and I get approx 300 to 320 miles out of a normal tank. I am down to 1/4 of a tank of gas and I only have 150 miles to show for it. The gas gauge is dropping faster than this last Iraqi war we just had!!!

Is my pump pushing too much fuel pressure and causing my car to still buck at just above idle and make the check engine light come on (no brainer on the MIL light). I saw a product from Weldon called the 14000 Dial-A-Flow which can change the voltage with a dial. Could this be a solution to lower power to my Walbro fuel pump power? Should I consider replacing my fuel return line with a larger one (say by as much as 2mm) to reduce pressure?

My major concern is fuel consumption but drivability is a big issue as well.

Here are the aftermarket bolt on power adders I have implaced on my car just in case you see a possibility of a conflict of any sort.

March underdrive pulley system
K&N air filter
Cervini's Ram Air hood w/ ram air kit
9mm spark plug wires w/ autolight double platinum spark plugs
70mm throttle body
Bassani X pipe w/o cats 2.5 inch (malfunction indicator light eliminators attached)
Flowmaster 2 chamber 2.5 inch
Jet Performance Superchip
BBK 1707 Fuel Pressure Regulator
Timing adjustor set at 16 degrees

Car is at 107,000 miles (3/4th of it is highway)

Thank you for any help and recommendations you may have in this matter!

[Badass_yellowGT]

aren`t the 98 great
i have not replaced my pump yet .i too bought a walbro pump and we have the stupid basket setup for the fuel pump in the tank i could not get mine to fit so i sent it back.

i beleive the problem you are getting is that with the pressure so high the engine is flooding with fuel, it`s like you have 24lb injectors thats how much fuel your trying to burn even tho your stock at 19lb and your maf is only getting a signal for 19lb injectors .you need to get the pressure down even if you have to buy the pump that ford made specifically for the 98 in the frpp catalog. thats what i`m getting, 255 is alot for a normaly aspirated engine 190 is more than a nuff. as for the voltage i`m not realy sure ask hammer he has the same model year as us.

the pressure at idle with vacum should be 20-22 psi and 40+ with no vacum attached.

how much did you pay for your fuel rail mines is welded to and i need to replace it.


ps. if you ever get the chance do the head swap it`s well worth it

[mustang98gt]

Badass_yellowGT,

Looks like were closer Ford Brothers in two different ways. Mine's Canary Yellow as well, and I'm just across the state line over in NH. I checked up on your website and brother, that is one nice yeller 'stang. I'll shoot you an email w/ a pic of mine here in a minute. Would you consider a NH GT in your club?

I will definately look at ditching the 255 lph and save it for a rainy day later in life aftermarket major mod. I just can't understand why it has to be so difficult (the 98's) being a 'bastard year'. I love my car to death, but I just wish mechanically, they would be absolutely the same as the 96-97, and even the 99's on up.

The vaccum rates you quote are what I'm getting. I did like the instructions were saying and capped off the vaccum line with my thumb while I adjusted the regulator.

I paid 10 bucks off ebay for my 97 crown vic rail. It was from a wrecked police cruiser that was being parted out. It didn't have a regulator attached but that was just fine with me because I decided to put on an aftermarket BBK instead anyways.

NOTE: I don't want to mislead you at all. The regulator does appear to be welded onto the fuel rail. When you look at the regulator (on the passenger side *WTF*) there is a black metal cover that rounds over it and bolts three different places; one of which is to the backside of the engine block (I say again WTF). After detaching that (your hands will be absolutely black after touching the heater core piping) and pulling the railing off, you will notice the regulator actually is held inside that cup that is welded to the rail. Its held in by a C-spring loaded clip. A pair of needle nosed (fine tipped mine you) should do the trick if you really care to look inside at it fully. First impression is that it is welded to the frame though, and it might as well still be, because you cannot fit a bigger nor adjustable regulator inside this 'cup'.

I'll be shooting you an email after this post with a pic and my contact info.

You have been a great help. I'll order up a new pump then from FFRP. 110 is too low and 255 sounded great at first, but man oh man. I'll let you know how the 190 will turn out.

[Badass_yellowGT]

sent you a pm