Do I use the older or newer style pump, I think the older style (95-97) should work, but cant find a definite answer, my fuel rail has two lines on it so I've assumed it is a return style.
If its return use the 94-97 pump...if not then grab a walbero pump...they just came out with a direct fit pump for the 98-04 return style cars...check the build date on your car...if its early 98 then you have a lot of choices...late 98 is the returnless style...I can't tell without seeing a pic though but it sounds like you need the 94-97 pump
You can't use a 96-97 fuel pump in your '98. It won't fit right.
The '98 is an oddball pump. It is a 2-speed pump and it is for a return style fuel system. My vehicle was built in Sept. 1998 and it has the 2-speed pump and a return style fuel system. I don't know when the change was made to returnless other than all of the +99 models are returnless.
If, by chance, your car has a returnless fuel system then it will have a fuel rail pressure sensor (FRPS). The '98 fuel pressure regulator is welded to the fuel rail (passenger side) in the return type system.
My original pump quit last year and the replacement was the pricey FoMoCo '98 GT pump. Had I done my research before the pump quit, I would have found that the SVT Focus pump "allegedly" fits with no modification. The Aviator pump "allegedly" fits with no modification. Let me go and dig up some threads about the compatible pumps for the '98 model. Many parts are unique, unfortunately, so they are expensive to replace.
edit
Here's a section of a thread on another forum. "Diesel" is replying to my post:
Thank you for posting hard (real) information. Please bear with me but I have a question or two. The SVT Focus pump will drop in without any modifications? No bucket modification? Plug & play?
No mods needed. It's plug & play. The bucket is nearly the same except for the top piece to accommodate the return line. Just swap the pump.
I have Mustang 1997-08-21 build date, and first I bought 170 liter/hr. fuel flow pump for 1998 Mustang from Ford Racing (I have it for sale ). Now I have Vortech and Focus SVT fuel Pump and it works very good. I read a lot post in many forums and there doesn't exist 1998 Mustang with returnless system. 1998 model has different fuel pump andbasket. If you want, you can send me PM with your Vin number and I can check which pump do you have 96-97 or 98.
Svt Focus fits with no modifications, you only need pump, without basket
Thanks for the picture. It is exactly like mine so your car has a return style system. "vitoGT" gave some very helpful info about the SVT Focus pump: plop it in (and you can use your old basket). Thanks, vitoGT!