Swapping Fuel Injectors

Need to replace failing injectors or just want to add some fuel?  Here's how.


Difficulty:    

Time Investment:  Under 2 Hours

Go to Pictures

Go to Instructions

Go to Tools Required

Go to Notes

Pictures:

Upper plenum has been removed, revealing the fuel rails.  You may wish to cover the opening in the lower intake so you don't drop something destructive intp the holes... like a bolt.	This is the connector on the wiring harness for the fuel injectors.  (92+)  The earlier style is a smaller connector with 4 pins instead of 7.	The quick connectors at the left side of the fuel lines should be disconnected in order to remove the fuel rail.	This is the entire 92 fuel injector wiring harness.  In this picture it is in the same orientation that it will be in when on the car.  The bottom most wire goes to the injector for cylinder #6.
A look at the fuel rail after removing the wiring harness.  Take note of the upper left injector in this picture.  The electrical connector is facing you rather than away like the other back injectors.  In needs to face that way to plug into the wiring harness.  In this picture, you can also see all of the bolt holes.	The fuel rail out of the vehicle with the injectors installed.	Notice the clip between the injector and the fuel rail.	Here is a shot of the injector clipped to the rail.  Although it looks like you have to use the tighter groove (as was done here) you can also slide the clip into the looser one.  Everything will end up tight once the rail is bolted down.

Instructions:

1.  Remove the upper plenum. 
(Simply leave the throttle body attached, unplug/unbold everything else, and lift off the upper plenum.) You may wish to cover the openings to the lower runners in order to prevent yourself from dropping something in there. Aluminum foil works ok for this.  You can also rip 3 paper towels in half and insert a half piece into each runner.

2.  In order to prevent gas from spraying everywhere, you need to depressurize the fuel system.  There are a few ways to do this:

• The fastest (and probably least safe) way is to cover the larger of the fuel line connections with a rag and use the tips of your fingers to release press up on the plastic insert under the connector and pull it off.  Fuel will shoot out, hopefully into the rag and you'll be done.  If you forget the rag, you may well take a face full of gasoline.  Experience has demonstrated that gasoline is not pleasant to have in ones eyes.
  
  
• Another way is to just pull a few plugs off of the injectors themselves and individually energize a one or two of them a few times.  Do this simply by connecting 2 wires to your battery terminals and quickly touching the other ends to the prongs on the injectors.  A few taps is all it takes.

3.  If you didn't just do it, disconnect all of the electrical connectors on the fuel injectors themselves.  These are far easier to remove than the big plug at the rear of the plenum.

4.  Disconnect both fuel lines. 
Both are conneced via easily removable quick connectors.  The key is to push up on the plastic inserts in the bottom of the caps and while pushing, lift upward.  If you've pushed the plastic pieces in far enough, the connector will lift right off.  It is worth noting that you can also just lay the rail over and leave the fuel lines attached if you wish.  Disconnecting them may make the rail easier to handle.

5.  Remove the rail/injectors.
There are 3 bolts in the middle, one holding down the fuel lines by the fuel pressure regulator, and one other one at the top right side of the rail.  You may find that the injectors are "glued" into the lower plenum and/or the rail.  To get them out, remove the clips holding the injectors into the rail, rock the rail back and forth, and gently pry up on it from different positions.   After you wiggle it around enough, individual injectors will begin to break free.   If they are really stuck, you can use a pair of channel locks to pull on the injectors directly.  Regardless, nothing is threaded here, once the clips are removed, the injectors should pull straight out of the lower plenum and the rail..

6.  Wipe out the holes were the injectors go on the top of the engine.

7.  Coat the new injector O-rings with a little bit of clean motor oil.

8.  Squeeze the clips with a pair of pliars to tighten them up a little. 

9.  Install the new injectors into the rail.
Insert the new injector into the rail and slide the clip over then end.  You can put the clip in either slot.  Looking at them, you may assume that you have to use the lower slot for the tighter fit.  This can be done (although it's difficult) with the 92+ injectors, but the earlier ones are just a hair longer and won't go.  It's perfectly acceptable to simply use the upper (looser) slot.  The clips are really more for installation anyway as once the rail is bolted down, the injectors can't go anywhere.

10.  Reinstall the rail.
You'll need to guide the end of each injector back into the appropriate hole in the engine.  Once that's done, push down firmly and put everything back together in the reverse order.

 

Tools:

• Socket wrench (3/8")
• Rag or a couple pieces of wire
• Channel Locks (optional)

 

Notes:

Injector Properties:

Impedance - The pre-92 year vehicles take low impedance fuel injectors.  The 92+ years take high impedance injectors.  If you aren't sure what you have, you can check the injectors with a multimeter.  Low impedance injectors will have a resistance of 2 - 4 ohms.  High impedance injectors will fall in the 12 - 16 ohm range.  Failing to use the right type of injector may cause the drivers to burn out or prevent your car from running properly.

Flow Rate - The stock  injectors for the 3.0 are rated at 19lb/hr.


Where to find:

The stock replacement injectors sold at your local parts store will likely cost a lot more than you really need to pay.  Comb eBay for used parts or for 92+, look for Accel brand injectors.

Pre-92, look for the turbo injectors from the 4 cylinder vehicles. 

92+, look for injectors fitting Ford applications. 


Upgrade Considerations:

Performance - There is still a debate as to whether upgrading the stock injectors will do anything for a N/A motor sporting the "typical" mods.  Some have claimed that in the older cars with the lower fuel pressure that upgrading to 27# turbo injectors increased the midrange pull.  In the newer vehicles, some have reported no noticable difference when upgrading.  This may not be a matter of who's right and who's wrong so much as a matter of the year, electronics, and condition of the old injectors on the car.  Who knows?  On Mike's IROC, upgrading to 26# injectors did nothing except smell rich during warm up and peg out the O2 sensor at WOT.  Using 21# injectors, the air/fuel gauge shows the mixture as very rich at WOT.  The car passed emissions but did show a level of unburned hydrocarbons just a hair below the legal limit.  Based on this info, it's up to you whether you want to try an upgrade.  In any case, keep in mind that more fuel doesn't mean more power without more air.  Air is usually the limiting factor when it comes to making more power. 

Starting - If you bump up the injector size a notch, you will notice that the car starts faster than before however two people have also noted that using 26# injectors and above seems to make warm/semi-warm starting take longer.

Economy - This should be obvious, but if you upgrade your injectors your car will run richer at startup and WOT.  This will result in increased fuel consumption during the warm up cycle and any time you put the pedal to the floor.  That said, if you upgrade and don't need to, it will just take the dollars out of your pocket and make some oil man somewhere richer.