Below are the procedures that I used in performing the replacement of six of my fuel injectors. I put them on this web page to serve as guidance for you, but do not guaranty the results nor do I proclaim this is the correct procedure, though I reference the Nissan Factory Service Manual, hereinafter ("FSM"), throughout. If you have any doubt on your capability in performing this replacement, take your car to a certified mechanic.

What you need:
1. Upper intake manifold gasket; part number 14033-89E00
2. Lower intake manifold gasket; part number 14032-89E01
3. Throttle body gasket; part number 16175-89E10
4. A.A.C valve gasket
5. New / remanufactured fuel injectors
    a. see the picture below, which depicts the two injectors with different connectors.
    b. The 90 -91 injectors have the metal clip (smaller) harness connector and the 92-94's have clip-type (bigger) harness connector.
    c. Also, Nissan made both blue and black dot injectors for our cars. I have been told you can use either one, but can't mix and match. I doubt it would hurt mixing and matching though, just so long as you get the right one for your car. The dot is on the harness connector.
    d. I picked up my remanufactured units for $37.95/ injector after the core deposit refund from Direct Automotive Products (www.directauto.com)

The injector on the left is a 92-94 injector, and the right is a 90-91, and probably an 89 too.

The steps I performed:
1. Release fuel pressure to zero
    a. I did this by unhooking the upper hose from the fuel filter after pulling the fuel pump fuse
2. Separate the accelerator cables from the throttle body.
    a. they easily just slide off. Tilt the butterfly valves back to get them.
    b. Remove the cabling and routing from the intake plenum.
3. Remove spark plug wires from spark plugs.
4. Remove the intake elbow leading to the throttle body.
    a. there are three bolts, the middle one is the longer one and routes the spark plug wires.
    b. These bolts are torqued at 13 - 16 ft lbs.
· For steps 6 - 9, basically remove necessary hoses and vacuum lines so you can free the plenum for removal. I took notes on a few of the items I might have forgotten when putting things back together.
5. Remove the A.A.C. valve
    a. there are four 5 mm hex bolts holding this in. remove the harness connector also.
    b. There is an "S" shaped hose connecting the AAC valve to the plenum, remove this also.
6. Disconnect throttle sensor
7. Disconnect the P.C.V. hoses behind the intake plenum
8. Disconnect vacuum hoses under the throttle body, from the E.G.R. control valve, master brake cylinder ,etc.
9. Remove the E.G.R. flare tube
    a. this is held on by two nuts. I think they are 10mm in size.
10. Remove the upper intake plenum
        a. there are eleven six millimeter hex bolts that hold down the plenum at 13 - 16 ft lbs.
        b. There is a special torque sequence that I observed in both loosening them and tightening them down. Please refer to the picture at the bottom of the screen for that sequence.

        Less the spark plug wires and the throttle body (my procedure keeps it attached to the plenum), your engine should look something like the above before taking the lower intake manifold off.  Pictures are courtesy of Matt Blehm.
11. Remove the lower intake manifold collector from the engine.
        a. Use the loosening sequence below for taking the manifold off and putting it back on.  Again, reference the picture at the bottom of the screen.
12. Remove the engine earth harness from behind the plenum.
13. Remove the fuel injector harness wires
        a. For the 92,93,94's this is easy, as you just apply pressure on the harness and pull
        b. For the 90 and 91's (and presumably 89's) there is a metal wire clip that you must pull out or partially out to remove the connector.
14. Remove fuel injector(s)
        a. I used a pair of pliers and gripped them tightly, turning the injectors back and forth before pulling upward. All came out somewhat easily, except my last one.
        b. There should be two O rings per injector for the 90 -91 injectors. I am not sure the 92,93,94 injectors have two. The lower O ring will likely stay in the fuel rail hole upon removal of the injector. Just stick your finger in and retrieve it. Be sure to replace with new "O" rings, per the FSM.
15. Replace injector(s)
        a. I applied motor oil to the O rings and carefully inserted the new fuel injector. Instead of just pushing downward immediately, you should turn it back and forth, while applying downward pressure. You will see and feel the injector seat in how it should be.  Before replacing, assure that the new ones spec out correctly with regard to resistance. The range of resistance allowed by Nissan is 10 –14 ohms.
16. Clean intake plenum, lower intake manifold, and intake runners.
        a. I used Carb clean and a Valvoline product. I sprayed a good amount of Carb clean down the intake runners and used a cloth to wipe the dirt out. You may want to try a toothbrush.
        b. Be sure to completely scrape away all remaining gasket material on both surfaces so as not to allow an intake leak after assembly.
17. Reinstall all parts in reverse order, keeping in mind the torque sequence and use the torque wrench so as to tighten the following to these torque specifications, per the FSM:
        a. plenum hex bolts 13 - 16 ft. lbs.
        b. lower intake manifold hex bolts, 13 - 16 ft. lbs.
        c. A.A.C valve bolts - 4.6 - 6.1 ft lbs.
        d. intake elbow bolts 13 - 16 ft. lbs.