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