It will effect your mileage very little. The 190lph fuel pump is a good choice. It is what I run as well.
Here is a write-up for a fuel pump install I did...it might come in handy for you.
To begin a in-tank fuel pump replacement you will want to make sure you have everything you might need to make the install go smoothly and with as little down time as possible. You will want the capabilities of getting the car up and off the ground for ease of install by using either a lift or a couple jacks and jack stands. Get a friend to help you out if possible along with some hand tools. Always be careful when working under a car. The least amount of fuel in the fuel tank makes it much easier so run it low or carefully siphon it out. The Walbro (190lph) pump I got from
www.50resto.com came with all the hardware included. This is quoted about the Walbro pieces: “190 & 255 fuel pumps that are marked w/ hardware will include all necessary hardware. 155 fuel pump includes sock only. The 255 fuel pump marked pump only will require the use of a HDW-9350D installation kit.” The hardware has the gasket for between the sending unit base and fuel pump inlet hole, the fuel line clips, crimps, wires, sock, pump, rubber hose and it’s clamps, and lock ring gasket (shown in pic). To go along with the below text here is a Acrobat file off of 50resto’s site that will provide better visualization to go along with the detail.
http://secure.50resto.com/images/do...s/fuel_pump.pdf
First you will want to release the fuel pressure. You can do this with one of 3 ways – 1: You can release the fuel pressure by the schrader valve behind the alternator. It looks like a tire stem valve once the cap is removed. Use a flathead screwdriver to pry in there and release the pressure while using a rag to catch any “built-up” pressure in the system. 2: You can go in your trunk or hatch on the driver side and go underneath the back panel and unplug the inertia switch. Then go ahead and turn the car on until the car dies. You will not be able to crank it up because you burnt the excess fuel off. 3: This is the easiest if time permits because alls you need to do is let your car sit overnight and the fuel pressure will release naturally. Disconnect the negative side of the battery as you will be working with electrically controlled parts.
Jack up the car safely and make sure the jackstands or jack isn’t protruding into the way where you can eventually drop the tank. Get another jack that is handy with a friend to help balance a piece of board to install underneath the fuel tank to help support it. When working under the car with the road dirt and potential fuel spray I think it is a good idea to wear some glasses to keep those things out of your eyes. Get under the car and see that there are two bolts (13mm) that hold on separate straps (2) to pin the fuel tank under the car. Undo the bolts and start to drop the tank a few inches. You will then see different connections into the top of the fuel tank. Just as well you will see the filler neck (where gas is pumped into) coming out of the side of the tank. The filler neck protruedes into the tank quite a few inches so what I did is shift the tank a little to the drivers side carefully to give me more “playing room.” I then began to pull out the filler neck by hand until it was completely out of the tank. There is a very small bolt that holds on a “handle” looking strap that goes over the filler neck which is 8mm in size. Make sure it is undone to move the filler neck where it needs to be. Keep the flexing to a minimum and only do what you need to do to get it out. Now you may lower the fuel tank a little bit more so you can have better access to the sensors/vents in the fuel pump.
Start removing the sensors by pulling up on them and using a broad flathead screwdriver to help you get under the grommets. You can do them by hand as well. Your going to need some A/C-Fuel Line disconnect tools from your local parts store to release the fuel lines off of your fuel pump sending unit (back passenger side of tank). There are two lines: 1: Sending line and 2: the Return line. I believe you can undo one of them with a flathead screwdriver (plastic clip) and the other one you will need to use the proper size fuel line disconnect tool to release it if not both of them. Now that all the grommets/vents/lines are disconnected you can start to lower the tank carefully while being VERY careful to keep any dirt from falling into the tank during the process that could cause premature pump failure. Put some paper towels in the holes to help any falling mistakes that might occur. Pull the tank over on a table or the ground for you to work on. Now is a good time to clean up the tank from any dirty debris all around it. You can also pour out all the gas and take it to a car wash and wash it inside and out and let it air dry for quite a while (depends on your time). I just left the gas in there and was careful about cleaning it and scraping dirt in the tank by accident.
Go ahead and start the fuel pump sending unit removal process by getting a brass punch (or wood) so a spark can’t be created around the fuel tank and it’s gas fumes. Draining and washing the tank will eliminate this problem. You DO NOT want to create a spark. Take the punch and put it against the lock ring and “pop” it counterclockwise to loosen it under the clamps. Remove the lock ring and gasket. Pay special attention to which way the fuel lines are pointing (that you previously disconnected) so you can install it later in the same fashion. You will need to turn the sending unit to remove the assembly out of the tank to reveal the pump/sock/wires. Go ahead and get your new fuel pump ready. Unbolt the two bolts that hold the fuel pump on the sending unit (5mm?). Undo the connection (rubber hose held on by radiator looking clamps) while removing the fuel pump filter (looks like a white sock). I used a screwdriver to pop it off. Cut the red and black wires where you have a enough room to splice into it with the new wires supplied with your new fuel pump (Walbro has them with it). Remove the fuel pump. Use your new rubber hose and match the wires together by color (solder them or crimp them). I just crimped mine nicely with the supplied crimps with the fuel pump. Put in the new pump and sock on it (put it in the SAME direction the previous fuel pump filter/sock was facing) while double checking the connections you just made. You are now ready to reinstall the fuel pump sending unit. It can only properly lay in one way and you can look in the fuel pump to see where it will lie at. Drop it in. Hopefully you were able to pick up a new lock ring and gasket to prevent leaks and have a cleaner install. Go ahead and install them in using the brass or wood punch to install it correctly. While the tank is out check the filler neck grommet (where the filler neck goes into). It will commonly be dry-rotted or rip upon removal of the filler neck. You can get one from your local parts store or at your Ford dealership. Put a thin bit of vaseline on the grommet to help it slide right in. You can do the same with the other vents/grommets.
Put the tank back on the jack/wood and begin to jack the tank back up and once you get some “wire room” start connecting everything back (the connections). Slide the tank a bit to the driver side at a little angle to reinstall the filler neck again being careful not to rip the new grommet you previously installed. Bolt the filler neck handle back on and jack the fuel tank up after you have reinstalled the fuel lines with new clips hopefully if they got broke or damaged. Jack the tank up all the way being carefully to make sure nothing is kinked upon pinning it up. Bolt the strap back up using those 13mm bolts again and remove the jack. It would be a good idea and highly recommended to replace your fuel filter. I run the Motorcraft FG800A or you can get one from your local parts store as well. Alls you need to do is go along the passenger back end of the car and see the fuel lines go in and out of a bracket where a filter lies behind. You can release it by using a flathead screwdriver to break or pop the plastic connections off that hold the fuel lines on it. You can then use the same screwdriver and start unscrewing the surrounding strap to loosen the hold-down bracket on the filter. Pay attention to which way the fuel filter is facing (some aren’t labeled to tell otherwise) so you can put the new one in the right way. You don’t want your fuel filter in backwards. Two new plastic clips should be included with your new fuel filter so you can use them on your fuel lines when you reconnect everything. Go ahead and lower your car back down and reconnect your inertia switch (if need be) and reconnect the battery. Prime your fuel system several times to fill up your fuel system before actually starting. Listen for the fuel pump to prime to make sure it is working properly. Start the car up and check for anything out of the ordinary. You are now good to go!
[other examples of going overboard].
