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911 Fuel Injector Replacement

Pelican Technical Article:

911 Fuel Injector Replacement

Bob Tindel


1-2 hours






Flathead screwdriver, 12mm and 14mm open-end wrenches, WD-40

Applicable Models:

Porsche 911 (1974-83)

Parts Required:

Fuel injector nozzles (6), fuel injector O-ring seals (6)

Performance Gain:

Renewed performance from your fuel injection system

Complementary Modification:

Replace the fuel filter
911 Fuel Injector Replacement

This procedure is for the 911SC, but the other 911s with CIS are similar.

Tools required: Screwdriver, 12mm and 14mm open-end wrenches; 10mm socket to remove air hose retaining bolt.

Parts required: Six new injector nozzles, six injector O-ring seals.

The fuel injector nozzles on an engine with a Continuous Injection System (CIS also called K-Jetronic) can become clogged gradually, with a decrease in power and performance. There is a tiny filter in the nozzle, and contaminants in the fuel eventually plug it. Also, the injector needle valve and seat can get partially blocked by deposits, causing an uneven fuel spray pattern.

The cure for this problem, and a way to rediscover lost performance, is to replace the injector nozzles. It is comparable to replacing the spark plugs, but easier. The injector nozzles are easy to locate--there are six of them, one at the end of each line coming from the fuel distributor to the intake manifold runners.

WARNING-This procedure should be done in a well-ventilated area, away from any ignition sources.

Wait until the engine is dead cold, and remove the two air hoses on the driver's side of the engine (one plastic one and one paper/wire one). Squirt a little WD-40 around each injector where it is seated in the intake runner. This will free it up and make it easier to remove. If you have metal injector lines, you can carefully tug on the injector and the line to pull the injector out. It needs to be moved upward only 10mm or so, and you will feel the O-ring snap out of the seat. Then you can disconnect the fuel line from the nozzle, using two open-end wrenches. The nozzle is 12mm, and the fuel line is 14mm.

If you have the plastic injector lines, don't pull on them. The plastic lines get brittle with age, and if you pull on them or kink them, they may break. Disconnect the plastic fuel lines from the injectors first, and then pull out the injectors. If they can't be pulled out by hand, grip them gently with a small pair of vice grip pliers (be careful not to mar the threaded part) and pull them out.

Lubricate the new O-rings seals, and slide them onto the new injectors.

Put a little WD-40 on the threaded part of the injector also, to make it easier to reconnect the fuel lines. Push the new injectors into the sockets in the intake manifold. You should feel each O-ring snap into its seat. Then reconnect the fuel lines to the injectors, and tighten carefully.

After the injectors are reinstalled, you will need to prime the engine before starting it, to refill the injector lines with fuel. Remove the air filter, turn the ignition key to the "on" position, and from inside the airbox, push up on the air sensor plate for about five seconds. You should hear the injectors hum slightly. Then replace the air filter and start the engine. Check carefully for any fuel leaks. If there are none, replace the two air hoses, and you are ready for a test drive, and to enjoy some horsepower that you may not have realized you lost!

Bob at Pelican Parts
Comments and Suggestions:
rigardo Comments: My SC starts well, but runs a bit roughly first minutes. I have to press little bit gas to keep it run. After warm up it idles fine. In operating temp engine makes sounds like broken stud sound during. I think sound comes somewhere near cylinder 6. Could it be a broken/leaking injector?

And fyi: head studs are new dilavars and are OK, valves are just adjusted, cylinder rings are new etc.
October 17, 2017
  Followup from the Pelican Staff: Sounds like a possible vacuum leak or worn valve guide. - Nick at Pelican Parts  
bryan Comments: I have a 1987 930 when I first start the engine I misses for about 30 seconds then smoothes out and runs fine even when engine is warm and I re start after 10 minutes do you think a sticky injector. thank you
September 10, 2017
  Followup from the Pelican Staff: Fuel delivery or valve issue. - Nick at Pelican Parts  
radar54321 Comments: 1987 ,3.2l carrera engine, one dead cylinder...had injectors r&r new
how to troubleshoot dead cyl. ?
plugs new, good compression
what to do now?
December 24, 2013
  Followup from the Pelican Staff: If you have good spark and fuel, there must be a base engine issue. Check static and dynamic compression. - Nick at Pelican Parts  
Hudson Comments: 1976 911S stumbles bad at about 2500-3000 rpm idles rough sometimes too... Checked for vacuum leaks by spraying carb cleaner with no results even by the injectors, replaced the vacuum lines, new fuel pump. Noticed one of my injectors is really really loose in the sleeve. Can pull the sleeve vertically about 1mm did this when the engine was running rough while parked and at operating temp. It smoothed out and ran fine instantly. Do you think this may be the problem?
November 11, 2013
  Followup from the Pelican Staff: If it smoothed out, you may have located the vacuum leak. Can you try replacing the injector seal? - Nick at Pelican Parts  
DAVE Comments: I have Motronic on my 86 Carrera and I had my injectors cleaned by Marren. They did a perfect job and sent me a copy of my injector fuel rate and compared each. The injectors came back within 2% of each other. When they were dirty two were not functioning within specs and they were definately not even.

I think this article should have an update describing the Motronic version and how it differs and also later versions. I think it is a waste to throwaway original injectors because they are dirty. Marren did mine for $25 each and gave me a printout on their performance. They look new and work great.

I had some trouble removing the injectors from the head and then pulling out the fuel rails. The injectors just pull straight out but may stick so it is important to apply enough force I didn't try WD40. Disconnecting the fuel rails first allows fuel to drain but you should catch as much as possible in a container. I also cleaned the fuel rails and had them replated with yellow zinc. I replaced the fuel filter as recommended by Marren and adjusted the fuel rail lines to reduce bending and kinking. I had some problem with refitting the rails and fuel lines so they matched and had a major fuel leak on restart. TO avoid this I sealed the connections with teflon tape but making sure the fuel line and fuel rail connectors meet evenly is important and is not mentioned here. My car runs much better and I recommend this maintenance for every Porsche that has over 100K.
May 22, 2013
  Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it.
- Nick at Pelican Parts
Barenecessity Comments: Bob, any advice/tricks on how to remove the fuel injector sleeves?
June 13, 2011
  Followup from the Pelican Staff: There may be little metal stakes holding them in, just remove the stakes and they pop / press out with a rubber mallet or soft faced hammer. - Nick at Pelican Parts  
Barenecessity Comments: Bob, I am about to follow your instructions above and change out the fuel injectors on my 83 911 SC. While I was ordering the injectors and sealing o rings, I noticed an injector sleeve part number 911-110-886-03-M260 in the catalog. Should the sleeves be replaced along with the injectors? If so, once the injectors come out, are the sleeves easy to remove and replace? Thanks for your assistance
May 29, 2011
  Followup from the Pelican Staff: I would replace the sleeves. There may be little metal stakes holding them in, just remove the stakes and they pop / press out with a rubber mallet or soft faced hammer. - Nick at Pelican Parts  
Larry Comments: Good advice. In my '79 911SC, the Injector Sleeves were shot as they get brittle and tend to leak over time. They install into the intake runners much like the injectors, captured by an o-ring. I used a large easy-out to first break them loose, then pull them out.
November 2, 2009
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
Angelo Comments: Hi Bob,how can I do for test my injectors nozzle? When I stop engine,the fuel burn inside of exhaust mufler,making a "boom" and a shoot fire on the tail pipe.And when I start again 3 minutes after,it running flooded...You understand-me? My inglish is not good.
My car is: 911S 2.7L '73 and use Mechanic Fuel Injection.The p/n of injector is: 901-110-271-00-M14
I appreciate your answer.Tanks,Angelo.
July 30, 2009
  Followup from the Pelican Staff: Hi there. You can take out the injectors and place them in a clear glass bottle and watch as the engine is turned on. If you're not sure what they should look like when injecting then compare one to the other. - Wayne at Pelican Parts  
wayne Comments: great advice
May 5, 2009
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts

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Page last updated: Fri 2/16/2018 02:37:18 AM