hope this is the right place. i have a 95 cadillac sedan deville 4.9l engine,i recently replaced the the engine with a remanufactured one(3yr unlimited milage),right after installation there was a problem with the nuimber 5 cylinder(oil and antifreeze leaking in) the heads were replaced and the car runs find now.however the gas milage is very poor(new wires,plugs,egr valve,o2 sensors,gas ,oil,air radiator,distributor,rotor,water pump were put in) on expressway i get 20mpg,but just driving around city it drops down to 7.9mpg any ideas to my promblem,the engine has 1200miles. also the idle is some time up and down but it never does it when i'm at the mechanic
FPR=fuel pressure regulator. First, pull the vacuum hose off of it (it's a black, round thing next to the throttle body, attached to the fuel rail) and spray in the nipple with WD-40, lots of WD-40. Then, reconnect the vacuum hose and blip the throttle about 15 times and drive the car around. See if that helps.
You don't need to replace all the injectors. Do a search here on how to perform a balance test--I'm too tired to type it all out.
Basically, you hit a couple of buttons on the dash, and you can cycle through each cylinder and shut off an injector. While doing this, you measure the RPM drop on the cylinder. If the RPM drop on one cylinder is a lot less than on the others, you have a leaking injector.