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Cleaning & Rebuilding 944 Fuel Injectors

Pelican Technical Article:

Cleaning & Rebuilding 944 Fuel Injectors

Michael Van Bibber


1 hour1 hr






10mm socket, small flathead screwdriver, adjustable wrench, 2 hose clamping pliers, shop rags, Q-Tips, 2 baggies and rubber bands, air compressor with air hose for compressed air, battery charger with 2ma setting, carb cleaner, ATF

Applicable Models:

Porsche 944 (1983-89)
Porsche 944 S2 (1989-91)
Porsche 944 Turbo (1986-89)
Porsche 944S (1987-88)

Parts Required:

4 fuel injector seal kits, 1 short length of hose to fit the fuel injector, hose clamp for same, 2 wires about 12 to 24 inches long, 1 push button, 2 alligator clips

Performance Gain:

Your fuel injectors will be spraying a steady stream of fuel once again

Complementary Modification:

Replace the fuel filter

I originally read this procedure on the Pelican Parts BBS. I tried the procedure and found it worthwhile, so I felt it would be useful to write it down as a tech article. While I kept the gist of the procedure intact, I added/modified a few of the steps that I felt made the procedure easier.

Thanks to "944Pilot" and "Porschemotorsport" for the procedure.

Warning/Disclaimer: This procedure involves working with your fuel system, as well electrical components in close proximity to your fuel system -there is a chance of seriously injuring/killing yourself or causing serious damage to your car if you screw up - gasoline burns, gasoline vapor explodes, and electricity can shock you, cause sparks, and other assorted unpleasant things - 'nuff said.

Tools Required:

  • 10mm socket
  • Small Flathead screwdriver
  • Adjustable wrench
  • 2 hose clamping pliers
  • Rags for clean up
  • Q-Tips
  • A couple of medium sized Baggies and rubber bands
  • 4 x Fuel injector seal kits (Pep Boys - Borg-Warner kit #274081, $2.49 each - comes with O-rings, washer, and the "hat")
  • 2 cans of carburetor cleaner
  • 2 cans of brake cleaner
  • New, clean ATF
  • 1 short length of hose to fit the injector
  • Hose clamp for the same
  • Compressed air source
  • Battery charger with 2ma setting


  • 2 wires, about 12 - 24 inches long
  • 1 Push button, momentary, normally open switch. (about $3.00 at radio shack)
  • 2 alligator clips

Removal Procedure:

1. Depressurize your fuel system -by pulling the fuel pump fuse and running the engine until it quits.

2. Disconnect the negative from the battery

3. Disconnect and remove your spark plug wires - now is a good time to inspect for damage - replace as necessary

4. Put a baggie over your distributor - secure with rubber bands (Note spilling fuel in your distributor can cause an explosion when you start the car)

5. Clamp the fuel feed and return lines running to the fuel rail

6. Disconnect the vacuum hoses running to the fuel regulators

7. Remove the plastic fuel rail cover (depending on how your wires and hoses are routed, you may have to do this earlier)

8. Disconnect the wiring harness from your fuel injectors, move the wiring harness out of the way

9. Unbolt the fuel rail from the engine

10. Pulling lightly, remove the fuel rail/injector assembly from the car, you can flip it upside down and rest it on the shock tower.

11. Using your drip pan and the adjustable wrench, loosen the large bolt on the front of the fuel rail and drain the fuel from the rail (NOTE: if you have to remove the bolt, DO NOT lose the sealing ball inside the bolt)

12. Pry the retaining clips off of the injectors

13. Grasp the injector and pull it out of the fuel rail - you may have to wiggle it a bit to work it loose - keep your injectors in order - make sure that injector #1 goes back in cylinder #1 (this isn't a requirement, but it seems like a good idea to me)

Cleaning Procedure:Now that the injectors are off, take a moment to clean the injector mounting points on the fuel rail with carb cleaner and a Q-tip. Do the same for the injector ports on the engine and the fuel injector wiring harness terminals

1. Spray the injector with brake cleaner to remove dirt, grime etc.

2. Work the little plastic "hat" off of the injector tip (Warning!: Don't damage the actual injector tip)

3. Slide the O-ring and plastic washer off of the injector

4. With the small screwdriver, work the top O-ring off (Where the injector connects to the fuel rail)

5. Spray it down with brake cleaner again, use a lint free towel to wipe the O-ring surfaces down

6. Fill the injector with carb cleaner, prop it up (not resting on the tip!!!) and let the cleaner drain through it - you can remove the O-rings, hats, and the like from the others while it is draining.

7. Attach the hose to the injector tip, again, being extremely careful not to damage it, secure with the hose clamp.

8. Now it is time to backflush the injector - to get the injector to open up, you must apply voltage to the injector. This is done with the battery charger. The trick is, you must "Pulse" the voltage, DO NOT apply constant voltage to the injector. You can do this by turning the charger on and off repeatedly, or, you can wire a simple circuit to make this much easier:

A. Take 1 wire, attach an alligator clip to one end, strip the other end.

B. Take the other wire, cut it in half, strip all ends, attach an alligator clip to one end, then wire the switch to the pieces of wire, making one wire again.

C. Connect the alligator clips to the injector terminals, the bare ends of the wire to the battery charger wires.

9. Fill the hose with carb cleaner,.

10. Turn on the battery charger, apply a compressed air source to the end of the hose. If you rigged up the switch assembly listed above, there will not be any power going to the injector until you push the button, if you didn't, you have to turn the charger on/off every couple of seconds, with the switch, just repeatedly push the button.

11. After the hose is empty, do it again.

12. Now flush the injector the other way twice.

13. Spray the injector down again with brake cleaner.

14. Time to reassemble the injector. Holding it tip up, slide the washer, O-ring, and then the hat from the kit. Flip the injector over and install the other O-ring.

15. Lube the O-rings with clean ATF, reinstall on fuel rail.

16. Repeat for the other 3 injectors

17. Fuel rail installation is the reverse of removal.

18. After installation, put the key in the ignition and turn the key to "ON" for a few moments to build fuel pressure back up.

19. Start the car.

This procedure took me about 60 minutes to accomplish. Since it was done, I've noticed the engine runs a little smoother, and the acceleration is a little quicker.

Michael Van Bibber (AFJuvat)

Comments and Suggestions:
Gusman Comments: I just replaced my fuel injectors on my 1885/1 944. This is after replacing the fuel pump, cleaning the fuel tank of old gas and dirty, replacing the fuel lines to the fuel pump from the tank which included replacing the screen since mine looked like it had been varnished. I had no issues installing the injectors, car started up right away but ran extremely rough. Could it be an issue with the injectors or maybe i should replace the plugs since the engine was running extremely rich??? Any ideas or suggestions?
June 29, 2017
  Followup from the Pelican Staff: hard to say. Can you isolate the rough running to a single cylinder? - Nick at Pelican Parts  
DeadPorsche944 Comments: The 2 mV setting for the battery charger should have been a 2 mA setting. This is the current setting the charger uses in the trickle charge mode. The injectors use 12 V to work. Current limiting should not be needed, it's just safer.
May 25, 2017
  Followup from the Pelican Staff: You are correct. Thanks for catching that, i will have the article updated.- Nick at Pelican Parts  
Tim Comments: I have a Snap-On injector tester. It has three different ways to test a injector. Single pulse, multi pulse and the wiring harness. Just connect it to a 12 volt battery source and plug it into a injector and begin test. Its good to have the proper equipment to diagnosis preOBD1 systems.
April 27, 2016
  Followup from the Pelican Staff: I have the OTC version of that tool, love it. - Nick at Pelican Parts  
Bukowski Comments: Can anyone recommend an injector tester or some other name for this? I have a battery trickle charger but nothing is user-adjustable.

There are some injector testers out there starting around $100, but the specific mention of 2 millivolts mv is difficult to place in the results from e.g. Google or Amazon, which only sometimes say anything about voltage.

Thanks for the interesting article.
January 18, 2016
  Followup from the Pelican Staff: I use an OTC injector tester. Runs them at a few different pulse widths. See if you can find of them used, might be the best bet for the cost. Otherwise they are a few hundred $. - Nick at Pelican Parts  
SlickV8 Comments: Hi. Done the above but the hat is still loose once clicked onto the injector. I have a spare green spacer in the kit. Should I use the green spacer and should the hat be really tight on the tip? Thanks
July 13, 2015
  Followup from the Pelican Staff: The sealing O-ring should be fairly tight, with only a small gap to the spacers. What spacers came off the injector? - Nick at Pelican Parts  
maso Comments: thanks for the reply Nick but if I used two six volt batteries in series, could the voltage be too much for the injector and damage it.
Obviously a car battery would be way too much input.
June 4, 2015
  Followup from the Pelican Staff: I can't comment as I haven't done it with batteries that way.

The battery in the car is used to fire the injectors, the issue would be if you hold the injector open too long and it sticks. I have an injector pulser from OTC, when I have to cycle or perform injector drop tests. - Nick at Pelican Parts
maso Comments: Tool requireds, last item battery charger with 2mv setting.
What is this?
I have been instructed to get two 6 volt battery. Connect them in series. Use alligator clips pulse the injector. IS this voltage too much? 2mV=0.2 volt.
Should I use one of those little compact 1.5 volt batteries
June 3, 2015
  Followup from the Pelican Staff: The small batteries will discharge too quickly. - Nick at Pelican Parts  
bobatious Comments: The filters in injectors are metal screens that filter the fuel, so over time they eventually clog. Definitely best to replace.
April 29, 2015
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
bobatious Comments: Embellishments I highly recommend:
- do replace the filters in the injector. These are included in many injector rebuild sets but not the BW one listed. This is the #1 spot for flow obstruction.
- if DIYing, buy or borrow an ultrasonic cleaner and clean in this with green clean or similar while pulsing the injector. Do it both directions. Flush with TB cleaner similar to suggested above then replace filter and fit o rings etc. I use a morse key with 12v supply connected via a normal injector plug for this.
- if timid about this or tempted to avoid replacing the filters, consider using an injector service place, that will do this labor, supply the needed parts, and flow test all for function and balance. Typically $25/injector.
April 29, 2015
  Followup from the Pelican Staff: Excellent recommendation. Definitely worth the $100 or so. I was not aware of any filter in the injector. Are you talking about the metal screen? - Casey at Pelican Parts  
Marty Comments: My 1977 924 is still leaking like crazy from the fuel distributor! I feel like it's going to start a fire. I think I will leave it alone. I'm still on a tight budget and consider this a low value car. I figured buying a 35 year old Porsche would require no maintenance and trick all my friends into thinking I'm rich! Also, My hood release latch is still doesn't release. Oh Well!
March 11, 2015
  Followup from the Pelican Staff: I would get that fuel leak fixed asap. Do not drive the vehicle.

Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
Marty Comments: 1 I have a 1977 924 fuel distributor that is leaking between top and bottom halves. I'm on a tight budget, working on a low value car. How can I fix the leak?
2 The hood release latch will not release, the cable is still connected to the assembly because if lever is pulled it has a spring return.
September 5, 2014
  Followup from the Pelican Staff: Replace the fuel distributor.

Replace the latch and cable.- Nick at Pelican Parts
Nolan197 Comments: Is there a way to get a new ball seal for the rail? when i pulled mine there was no ball inside the end cap. I would assume this is there for a reason?
June 17, 2014
  Followup from the Pelican Staff: Not sure. Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
boeboe Comments: is it very wrong if u pull the injectors and 3 out of 4 hats are missing, could have been done by the previous owner. but if not, is it able to damage the cilinders or the valves?
May 23, 2014
  Followup from the Pelican Staff: I would install new hats. When you found it this way, was it running well? Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
Jay_IL Comments: I'm looking to clarify what ATF is? Are we talking about Automatic Transmission Fluid? I would think you would lubricate the o-rings with a high temp silicone grease.
May 23, 2014
  Followup from the Pelican Staff: ATF - automatic transmission fluid. I prefer to use dish soap or the fluid the O-rings seal to lubricate them. for fuel O-rings, I always use dish soap. - Nick at Pelican Parts  
John_AZ Comments: There is a mesh screen/filter inside the top of the injector. If you can find a source for the "Bosch Universal Crush Filter" you can remove your old screen and then do the cleaning. Install the screen when finished.
October 2, 2010
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts

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Page last updated: Fri 3/16/2018 02:19:02 AM