LT1 injector swap...

[Steve n Seattle]

Seeing how I have 145,000 miles on the stock LT1 injectors, I ordered some 1998 Trans Am injectors from an LS1 engine (over eBay). The 1998 LS1 injectors were rated at 28.8 #/hr in the stock 4 bar (58 psi) fuel rail. In my 1997 LT1's stock fuel rail (3 bar, or 43.5 psi) the injectors should be 24.9 #/hr... compared to my the stock 24.4 #/hr the 94-97 LT1 engines came with. The PCM should be able to pull a small amount off the pulse width if needed, but functionally they're the same.

The only catch with the LS1 injectors is that the retaining clips which secure the injectors to the fuel rails won't work since the LS1 injectors have grooves on two sides that the clips won't hold, and no grooving on the sides that the clips would normally engage. This doesn't affect the function of the injectors at all as the rails are bolted to the intake manifold and prevent the injectors from "popping out" of the rail or manifold once the injectors are in place and the fuel rails tighten down.

Here's the procedure the best I can recall:

1) Let car sit for about 2 hours so the fuel rails aren't pressurized and the engine is cool.

2) Remove gas cap

3) Look to the rear of the intake manifold and locate the cap that covers the fuel rail/regulator's Schrader valve. It’s the same design as those used in tire valves, and the cap looks similar as well.

4) Place a shop rag or towel behind/around the valve

5) Using a dull but narrow object, open the Schrader valve to vent off the last of the rail pressure. After two hours of sitting mine didn't vent nearly anything.

6) Unclip the wiring harness clamps that are connected to the fuel rails. The clips will stay connected to the rails, just open them up and push the wire harness behind the intake & fuel regulator. I found that removing the small value line to the regulator, and rotating the open clips 180 degrees helps with positioning the harness.

7) Using an 8 mm socket, remove the four (4) fuel rail bolts which secure the rail to the intake manifold.

8) Disconnect the wire harness from the eight (8) fuel injectors. To disconnect the electrical connector, just push on the U-shaped wire lock from the outside edge of the injector. The wire is there to lock the connector on the injector by having the wire lock underneath a barb on the injector housing under the harness-connector. To remove the connector, push the bottom of the "U" wire towards the fuel rail, and pull up on the black connector/cap as the wire starts to bow outwards.

9) Each injector connector was numbered for the appropriate cylinder on mine, although earlier years with batch-fire injection (like the 1993 F-body) may not need them. Just the same, you might want to tag them with masking tape if they aren’t labeled already.

10) Remove the rails/injectors as a single unit. You'll need to wiggle them a fair bit at first, them use a screw driver or crescent wrench to pop them up. Do NOT pry on the fuel line cross-over! (Thanks Ellis) Just use the ends of the fuel rails until you pop the front up then go to work with your hands. BE CAREFUL

11) Once the unit is up, check EVERY injector to make sure they each have an o-ring attached to the bottom. If one is missing an O-ring, use some needle-nose pliers to CAREFULLY remove the o-ring from the intake manifold where it was left behind. The O-rings do not "seat" in the intake, but instead "rub" into a beveled hole. If you are not careful, the o-ring will fall into the intake. While you'll lose your o-ring, the engine "should" be ok... the silicone o-ring will just burn up in a cylinder... but I wouldn't recommend it.

12) Swing the rail/injector assembly forward until you can reach each injector comfortably, being careful not to mess up your regulator and wiring harness that is in the rear.

14) Place a shop rag or old towel under the fuel rail. As each injector is removed, some fuel from the fuel rail will follow it. Plan on wearing gloves and being in a well-ventilated area (outside in a car port or parking lot is preferable).

15) Remove the retaining clips by sliding them on the fuel rail. Each fuel rail has two small ridges that the retaining clips side on. To get the clips off the fuel rail (if you're going to LS1 injectors), slide them forwards and off the front of the rails. You'll probably want to remove them front-to-back for this reason. (I.e. Cylinder 1, then 3, then 5, the 7)

16) Remove the injectors by pulling straight down. As EACH injector is removed, make sure there is an o-ring on the injector top. If not, use the needle nose pliers to remove the stuck o-ring from the fuel rail.

17) Install the new injectors by lightly oiling the o-rings and mounting them up into the fuel rails, ensuring they seat to make the o-ring disappear from the side-view, then secure them with the retaining clips (if you are using LT1 injectors).

18) position the rail-injector-regulator assembly back over the intake manifold, and generally align the eight injector tips above the intake manifold holes. To ensure the rails are in the proper position, place the 4 fuel rail bolts in the fuel rail holes and hand thread all 4 bolts down a few turns into the intake manifold holes. Make sure you watch for the wiring harness in the back, and the vacuum line for the regulator that may have gotten routed under the rail during this process.

19) Push down on the fuel rails to carefully seat all the injectors in the proper holes.

20) Finish hand-threading the fuel rail bolts down to the fuel rails and snug them up to keep the rails in place. I don't know what the torque rating is on these bolts, but I just snugged them up and gave them a 1/4 turn to make sure they don't back out.

21) Secure the wiring harness in the 2 fuel rail clamps.

22) Re-connect fuel regulator's vacuum line (if disconnected)

23) Replace the cap on the fuel rail Schrader valve.

24) Connect the 8 fuel-injector connectors. Make sure the harness clips to the same injector it was removed from and that each "clicks" the U-wire retainer around the new injector's side-barb (plastic bump) to secure it on the injectors.

25) Replace the gas cap

26) Turn the key to "on" but don't turn over the car. Let the fuel pump pressurize the fuel rails for a few seconds.

27) Turn off the key and repeat 26 once or twice.

28) Start it up and watch for any fuel leakage from a faulty o-ring. Make sure you have a flashlight and try to do it on a sunny day so you can see the rear injectors well.

If everything checks out fine, you're done.

Steve

P.S. I had some new injectors for the install with 5000 miles on them, so I knew they were working fine. For those that want to make SURE you don't have a leaky injector (which can lead to hydro-lock and engine failure) you will want to pressurize the fuel lines (steps 26 and 27) after item #17, then procede with the install from there. I personally wouldn't try this without the injector retaining clips installed however... things may get messy if an injector pops out!

Oh yeah, the LS1 injectors are much lighter than the LT1 units (due mostly to coil size I believe)... cut nearly 1/2# off the front of my car.

[Steve n Seattle]

I know it looks like a lot of work, but the only tools you need are:

- 8mm socket (w/wrench)
- needle-nose pliers
- any average cresent wrench or screw driver (for prying)
- large old towel (or some shop rags)
- flashlight (even on a bright day the rear of the engine is dark)
- a cap-full of motor oil for lubing the o-rings

Might want to have a magnetic pick-up tool for clips/bolts that could fall as well.

Total time: 20 minutes