REPLACING FUEL INJECTORS ON A MKIV 12V VR6
The following procedure describes how to remove (and replace) the fuel injectors on a MKIV 12v VR6, one of which is shown below.
Poorly operating injectors can cause decreased gas mileage, rough idle, decreased engine power, engine surging and increased emissions. Sometimes the CEL will even come on, causing you to fail an OBDII emissions test. I removed my injectors because the fuel trim values reported by VAG-COM indicated that my engine was running close to 10% lean at elevated engine speeds (10% is the limit for triggering a CEL). Since the injectors had more than 216k miles on them, it was possible that the injectors had become clogged by fuel deposits over time and the ECU was compensating for the decreased flow rate by increasing the injector pulse duration. I sent the removed injectors to WitchHunter Performance for ultrasonic cleaning and replacement of filter baskets and o-rings. The results of this cleaning procedure are documented HERE.
The procedure below is based on a '99.5 Jetta GLS VR6, but should be applicable to all MKIV VR6s and similar on many later model VWs.
The following items are required to perform the procedure:
- Small screwdriver
- 5mm hex wrench or socket
- Spring clip pliers (regular pliers will work fine)
- Two rods ~ 5/16" in diameter, if you want to plug the fuel lines (I used a screwdriver and 1/4" socket extension)
- Roll of wide tape
REMOVING THE INJECTORS:
1. Open the driver's door and pop open the door that covers the fuse panel, as shown below.
2. Remove the fuse for the fuel pump (#28), indicated by the red arrow in the picture below.
3. Start the engine and let it stall out. This will remove the pressure from inside the fuel lines so that you won't get sprayed in the face with gas later on.
4. Loosen the gas cap to vent any residual pressure. This step may not be necessary, but it can't hurt.
5. Remove the engine covers and upper intake manifold from the top of the engine by following the appropriate steps in this DIY by FaelinGL (Mike).
6. The injectors are located on top of the lower intake manifold, as indicated by the red arrows in the picture below.
7. Before proceeding, cover the holes in the lower intake manifold with some tape (red arrow) if you haven't already.
8. The wires for the fuel injectors (as well as the rear knock sensor) are contained in a support (yellow arrow in picture below) that is attached to the fuel rail (green arrow) in three places (blue arrows). Before removing the support, there are 6 retaining clips (red arrows) that first need to be popped open in order to remove the wiring.
9. The picture below shows the clip that secures the wiring for the #3 and #4 cylinder injectors. To pop open this and the other five clips, use a small screwdriver placed in the slots indicated by red arrows to gently pry them open. The yellow arrows in the picture show how the support is attached to the fuel rail (it's simply clipped on to both tubes).
10. The picture below shows how the individual wires for injector #1 (rred arrow) and injector #2 (yellow arrow) are secured below their retaining clip.
11. Once all of the retaining clips are open, carefully remove the wiring from the support, unclip the support from the fuel rail and manuever the support out from around the wiring. The picture below shows the support removed.
12. The following three pictures show how the injectors are oriented in the lower manifold. Their orientation is important since the upper manifold sits just above the injector harnesses and you want to avoid any interference. The injectors for odd numbered cylinders are oriented so that the electrical harness is roughly straight up, while the injectors for the even numbered cylinders are rotated approximately 45° counter-clockwise (towards the passenger's side). The injector for cylinder #1 is rotated slightly clockwise (towards the drvier's side) so that there is no interference with the wiring support when installed.
13. Remove the electrical harneses from all six injectors by pressing in on the two retaining clips (red arrows in picture below) and then pulling up on the harness (yellow arrow).
14. Work the wiring and harnesses for the six injectors out from underneath the fuel rail.
15. Disconnect the wiring for the rear knock sensor from the top of the valve cover. The two retaining clips, indicated by the red arrows in the picture below, should easily lift up out of their holes in the valve cover. You shouldn't need to undo the wiring from the wiring clips, but can if the clips so not easily come out of the cover.
16. Pull the vacuum line T-fitting off of the fuel pressure regulator on the fuel rail, as shown below.
17. Move the injector and knock sensor wiring out of the way (red arrow in picture below).
18. Unclip the flexible fuel lines from their retaining clips (red arrows in picture below) by placing a small screwdriver in the groove at the top of each clip (yellow arrow) and carefully prying it open. The left clip in the photo has already been opened.
19. Unclamp and remove the fuel lines from the fuel rail, as shown in the picture below. Use a rag or paper towel to catch the small amount of gas that will come out. Also, note the position of the clamps on the hoses before removing the clamps. The clamps should be put back in the same position so that the tabs won't sit underneath the upper manifold when it's reinstalled. This is just a guess, but you probably don't want to have to take the manifold back off to work on the fuel lines if need be at a later date.
20. If the car is going to sit for a while for whatever reason, then I recommend that you plug the fuel lines, as shown in the picture below. Mine sat for a week and a half while I was on vacation and the injectors were shipped out for cleaning and I didn't want the garage filling up with gas fumes. If you're reinstalling injectors immediately after removing them, then this step is not necessary.
21. Pop off the clips that secure the injectors to the fuel rail (red arrows in picture below) by pulling straight up on them. They're "springy" and should pop off easily.
22. The picture below shows one of the clips partially removed. Note the slots in the side of the clip where the flange on the fuel rail fitting sits.
23. The picture below shows one of the retaining clips completely removed.
24. The picture below shows the proper depth of the injector in the fuel rail fitting. The retaining clip slides into the groove in the injector (red arrow) and around the flange on the fuel rail fitting. Note that when the injector is sitting in the fuel rail fitting at the proper depth, the distance between the flange and groove is appoximately equal to the width of the groove.
25. The fuel rail is secured to the lower manifold by four 5mm hex bolts in locations indicated by the red arrows in the picture below.
26. The picture below shows a close-up of one of the fuel rail bolts. Remove all four of these bolts.
27. Carefully pull the fuel rail off of the injectors by pulling a little at a time at various points along the length of the rail, as shown in the picture below. The o-rings secure the injectors into the rail pretty good, so you may need to give it a good tug. Just don't pull so hard as not to bend the fuel rail. It doesn't matter if the injectors stay in the manifold or come out with the fuel rail. All of my injectors stayed in the manifold, but some were loose and close to coming out with the rail.
28. Carefully wiggle/rotate the injectors out of the manifold. You can use the harness on the injector for a little bit of leverage, but don't put too much pressure on it or it could possibly break off. The injectors should come out eventually with gentle wigging/rotation so don't get impatient if it seems like they're completely stuck. Most likely they're not.
29. Check the fuel rail fittings for any o-rings that might have popped off the injectors and remained in the fittings.
30. Also check the holes in the lower manifold for any o-rings that might be present. Note: If you look into the injector holes in the lower manifold for the front (even) cylinders, you should be able to see the intake valve for each cylinder (green arrow). Mine showed very little deposit on the valve even after 216k miles!
31. If the car is going to sit for a while, cover the injector holes in the lower manifold with tape so that nothing falls in.
REINSTALLING THE INJECTORS:
The reinstallation of the injectors is done by simply following the above steps in reverse. Here are some simple tips which should help make the process easier:
- Apply some gas or a small bit of clean oil to the injector o-rings before pushing the injector into the manifold or fuel rail. They'll go in much easier this way.
- Figuring out how far the injectors should be pressed into the manifold and fuel rail can be a trial-and-error process. I recommend fitting the injectors into the manifold first and then pressing the fuel rail on. Use the picture in Step #24 to gauge if the injector is positioned properly. If it isn't, move the injector in the appropriate direction so that the flange and groove look like they do in the picture. When the groove and flange are related this way, then the injector clips will slide on very easily. Since the fuel rail is bolted a specific distance away from the manifold, you only need to correctly position the fuel rail end of the injector. The manifold end of the injector will be positioned in the manifold accordingly.
- Torque the fuel rail bolts to 7 ft-lbs if you have a torque wrench.
- Don't forget to reinstall Fuse #28 or the car won't start.
Congrats on a job well done. Have a or two.
As always, do this procedure at your own risk. I am not responsible for any mistakes in the above procedure or those that you make while performing it.